Oxidative ligninolytic enzymes and their role in textile dye biodegradation: a comprehensive review

GSH

glutathione

HBT

hydroxybenzotriazole

LDAE

lignin-degrading auxiliary enzyme

LEs

ligninolytic enzymes

LiP

lignin peroxidase

LME

lignin-modifying enzyme

MnP

manganese peroxidase

PAHs

polycyclic aromatic hydrocarbons

VA

veratryl alcohol

VP

versatile peroxidase

WRF

white-rot fungi

Rapid industrialization, globalization, and urbanization have resulted in unforeseen problems related to ecological damage (Ngo & Tischler 2022). One of the main concerns today is the rapid growth of the textile sector, which has the potential to release synthetic materials and toxic colors into the environment, negatively impacting shared resources, including soil fertility, aquatic life, and ecosystem integrity, and causing health problems in human (Natarajan & Manivasagan 2020; Aragaw & Bogale 2023). Water quality deteriorates daily because of these contaminants (Thapar et al. 2021; Al-Tohamy et al. 2022). The main causes of toxicity are the stability of pollutants and their resistance to various physical, chemical, and biological degradation routes (Eibes et al. 2015). Owing to their eco-toxicological properties, dye-containing textile effluents have been extensively studied as potential ecological hazards (Lellis et al. 2019; Patel et al. 2022; Sultana et al. 2022). As these substances change the ability of aquatic biota to photosynthesize, reduce gas solubility, and increase both chemical and biological demands for oxygen, they pose a major environmental threat and lead to an unbalanced ecosystem (Sarkar et al. 2017). Therefore, these harmful compounds must be removed before wastewater is discharged into the environment (Sosa-Martínez et al. 2020).

Synthetic dyes are the most dangerous compounds commonly used in the textile, cosmetic, printing, paper, and pharmaceutical industries (Kalsoom et al. 2022). Auxochromes (electron-withdrawing or electron-donating groups such as –NH₂, –COOH, –SO₃H, and –OH) and chromophores (with conjugated double bonds (–C═C–, –C═N, –C═O, –NO₂, –N═N) and quinoid rings) are both present in the dye molecules (Bilal et al. 2017). Direct dyes, azo dyes, anthraquinone dyes, reactive dyes, vat dyes, basic dyes, aniline dyes, mordant dyes, macromolecular dyes, sulfur dyes, metalized dyes, pigment dyes, naphthol dyes, premetallized dyes, and developed dyes are only a few of the many types of dyes used daily (Abdi et al. 2020). Reactive dyes are highly contentious owing to the resistance of their complex aromatic compounds to natural biodegradation (Siddeeg et al. 2020).

More than 20% of the dye is lost during textile processing owing to inefficiencies in the dyeing process (Selvaraj et al. 2021). Depending on the manufacturing technique used, different industries have distinct dye effluent compositions and properties. Textile wastewater exhibits variability in terms of pH (5.5–11.8), temperature (21–62 °C), and additional factors including dissolved metals and suspended particles (Yaseen & Scholz 2019). It is essential to design a treatment system that functions effectively under changing environmental conditions. To mitigate textile dye pollution, many physicochemical techniques have been employed. However, these methods are deemed financially infeasible for the large-scale treatment of industrial waste because of their undesirable sideeffects, which include high cost, poor efficiency, secondary pollution, deposit waste problems, and inability to react and treat a wide range of colors (Rajasimman et al. 2017; Aragaw 2020; Aragaw & Angerasa 2020; Oliveira et al. 2020; Aragaw & Alene 2022).

Microorganisms, predominantly fungi and bacteria, produce various enzymes, primarily ligninolytic enzymes (LEs), such as, laccase, LiP, MnP, versatile peroxidase (VP), and feruloyl esterase to degrade woody biomass (Kumar & Chandra 2020; Civzele et al. 2023). These microorganisms have been identified and evaluated for their biodegradation efficiency of lignocellulosic waste during woody decay (Janusz et al. 2017). Although several microorganisms are sources of LEs, white-rot fungi (WRF) are the most studied microbes that can degrade persistent or toxic environmental pollutants (Yadav & Yadav 2015).

The biodegradation of cellulose-based biomass by various microorganisms produces glucose and carbon dioxide (Barbosa et al. 2020). Biomass biodegradation requires different enzymatic systems and is generally categorized as a lignin-degrading auxiliary enzyme (LDAE) or a lignin-modifying enzyme (LME), which is simply called LE. LDAEs are unstable in independently degrading the lignin part of biomass, which requires additional enzymatic activity that enables complete biodegradation through the sequential action of various proteins and hydrogen peroxide (H₂O₂) (Janusz et al. 2017). LEs have gained attention for the biodegradation of not only ligninolytic biomass but also hazardous pollutants, such as textile dyes (Chowdhary et al. 2019; Chauhan & Choudhury 2021). For example, MnP has been used to oxidize aromatic amines and phenolic compounds in wastewater via one-electron oxidation to produce more reactive free radicals (Saikia et al. 2023). Using LEs in bioremediation is environmentally friendly and is used for efficient biodegradation and detoxification of textile dyes.

Hence, the reported LE-based biodegradation of textile dyes must be summarized, synthesized, and evaluated in a single reference paper to provide state-of-the-art information in the field of oxidative LE-based biodegradation of textile dyes. This review aimed to evaluate LEs and explore their roles in the biodegradation of hazardous textile dyes. We conducted a detailed literature review, synthesis, examination, and discussion of various LEs, their sources, and efficiency and mechanisms of dye biodegradation. Moreover, the factors affecting the activity and production of LEs during dye biodegradation, their application, and the limitations of LEs are highlighted.

In most studies, enzymes have been shown to play key roles in the decolorization and biodegradation of dyes. Oxidoreductive enzymes are the common classes of enzymes involved in the biochemical reaction during the biodegradation processes (Wu et al. 2022). Biodegradation involves two steps: reduction cleavage of dyes, followed by oxidation of the dye-transformed substances (Kamal et al. 2022). These enzymes are responsible for altering the oxidation states of dye molecules by moving electrons or hydrogen atoms from the manufactured substance (acceptor) to the reduced substrate (donor). Dyes can be converted into non-toxic substances through multiple redox reactions (Khatoon et al. 2017). Many oxidoreductases require cofactors such as nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADP⁺), flavin adenine dinucleotide (FAD), or transition metal ions to facilitate electron transfer.

Fungi: are major sources of LEs. Depending on how they attack and decompose, ligninolytic fungi can be divided into three groups: brown rot, soft rot, and white rot (Parthasarathy & Narayanan 2014; Ingle et al. 2019). White-rot basidiomycetes are mostly found in hardwood and are the most effective lignin degraders, producing a white powdery fibrous material in the process. Consequently, they are known to be the best producers of LEs. The ligninolytic system of WRF is not uniform; several WRF have been shown to contain one or more LEs (Debnath & Saha 2020). However, little is known about the LEs produced by other kinds of fungi, such as ascomycetes, which are soft-rot fungi that attack lignin in an advanced state of wetness and are primarily found in aquatic environments, such as marine ecosystems (Niu et al. 2021).

Bacteria: Some bacterial strains have also been identified as potential sources of LEs. For instance, Aneurinibacillus aneurinilyticus, Panibacillus sp., and Bacillus sp. have been found to degrade and decolorize synthetic dyes isolated from pulp paper mill sludge (Ojha & Tiwari 2016; Kumar & Chandra 2020). Additionally, the involvement of Streptomyces in lignin decomposition has also been reported (Kumar & Chandra 2020).

Algae: Some algal species have been found to produce LEs. Studies have shown that certain microalgal species can produce enzymes capable of degrading lignin (Abd Ellatif et al. 2021; Alsukaibi 2022). They are cost-effective and efficient organisms for biodegradation of certain pollutants. Microalgae use hydrolytic enzymes to break down dyes and their commercial production processes are affordable (Otto & Schlosser 2014; Abd Ellatif et al. 2021).

Yeast: Although there are only a few studies on the performance of yeast LEs, they can degrade azo dyes (Goud et al. 2020; Alsukaibi 2022). Yeasts possess several advantages such as their ability to withstand extreme pH levels, high osmolality, and low temperatures. In addition, they can break down various harmful pollutants through the production of specific enzymes (Ali et al. 2021). Decolorization and detoxification of azo dyes by MnP-producing yeast strains isolated from wood-feeding termite (WFT) gut symbionts belonging to Meyerozyma caribbica have been reported (Ali et al. 2022).

Extremophiles: are also LE-producing microorganisms. Extremophilic LEs are generally excreted by bacteria, fungi, and actinomycetes and are capable of a wide range of substrates in normal to extreme environments (Kumar & Chandra 2020). Thus, these microorganisms are interesting sources of LEs with extreme stability under extreme conditions, such as high temperature, pressure, or radiation, as well as geochemical characteristics such as high salinity and pH (Zhu et al. 2022). LEs in extreme environments possess adaptive features and structural properties, such as specificity, and contain different chemical structures (including saturated fatty acid bridges and disulfide bridges) that can retain adaptive properties and stabilities.

Thus, resistance to oxidative stress may be an adaptive mechanism (Jeong & Choi 2020). In recent years, the use of thermophiles in various industrial processes has attracted increasing interest because of their importance as sources of thermostable, commercial enzymes (Aragaw et al. 2022). Thermophiles have also been demonstrated to have intriguing uses in the bioremediation of heavy metals and the breakdown of various chemical compounds, such as dyes (Nzila 2018). It is anticipated that thermophiles possess an exceptional ability to adjust to oxidative stress, which encompasses oxidative damage resulting from dye biodegradation (Baker et al. 2021).

Plants: The most well-known LEs in plants are laccases, which are extracellular glycoproteins comprising monomeric proteins and sugars. Many plants, including the Japanese lacquer tree, mango, mung bean, peach, tobacco, and maize, contain laccase (Wikee et al. 2019). In plants, laccase is used for various purposes, including lignin synthesis (Pandi et al. 2019), iron oxidation from Fe (II) to Fe (III) (Sakamoto et al. 2015), and the regeneration of injured tissue. Lignin production plays an important role in plant structure and defense.

In addition to laccase, the ability of plant peroxidases to remove contaminants from synthetic and industrial effluents has attracted interest (Kurnik et al. 2018). Plant peroxidases are class III peroxidases that share the same catalytic mechanism as microbial peroxidases (Petronijević et al. 2021). Plant peroxidases include soybean peroxidase, horseradish peroxidase, and turnip peroxidase (Ahsan et al. 2021). Horseradish peroxidase was once thought to be the most promising plant peroxidase choice (García-Zamora et al. 2019), but it appears to be overtaken by other peroxidases (and microbially produced laccase). Biodegradation of dyes and phenolic contaminants has been studied using a variety of immobilized plant-derived peroxidases to improve enzyme robustness and biocatalytic effectiveness (Panadare & Rathod 2017). Researchers have reported enzyme-catalyzed biodegradation and transformation of numerous dyes using immobilized plant peroxidases (Sellami et al. 2022). Although some plant peroxidases have been reported to effectively remove phenols, the application of plant-derived enzymes is supported by microbially produced enzymes, which can be recombinantly produced more easily and inexpensively than plant peroxidases (Garg et al. 2020).

Insects: LEs produced by insects carry out delignification. Different insects have been studied for their secretion of LEs, such as the Nephotettix structures (salivary glands) (Wang et al. 2018), Manduca sexta (Malpighian tubules, midgut, fat body, and epidermis) (Asano et al. 2019), Reticulitermes flavipes (gut) (Calusinska et al. 2020), and Tribolium castaneum (cuticles) (Mun et al. 2020). In insects, LEs primarily serve in cuticle sclerotization and coloring, oxidation of hazardous substances, and polymerization (Zhang et al. 2018).

Although non-ligninolytic oxidoreductive enzymes are involved in dye degradation, this study covers only the specific catalytic mechanisms of LEs.

Laccase exhibits significant bioremediation potential owing to its ability to effectively oxidize a diverse array of substrates. These enzymes belong to the oxidase family and possess a catalytic site containing four copper atoms. The unique ability of laccase to degrade various pollutants makes it valuable for the breakdown of xenobiotic chemicals during textile wastewater treatment (Alsukaibi 2022). In the process catalyzed by laccase, dye compounds undergo oxidation by O₂, with the transfer of one electron occurring sequentially among copper atoms until O₂ is ultimately reduced to water (Gao et al. 2022). Multiple copper oxidases are included in the basic structure of laccases (p-diphenol: dioxygen oxidoreductase). They are produced by specific plants, animals, and microbes, and they are catalyzed by the oxidation of many reduced phenolics and aromatic substrates with the ordered reduction of subatomic oxygen to water. Isoenzymes are produced by genes that encode various laccase structures (Karigar & Rao 2011).

Ortho-, para-, amino-, polyphenolic, polyamine, lignin, aryl diamine, and a few inorganic ions are among the substances that are oxidized by intra- and extracellular laccase. Laccases can undergo different biochemical reactions, including oxidation, decarboxylation, demethylation, and polymerization of lignin into phenols, which are also responsible for producing humic materials. Therefore, laccases have several biotechnological applications including bioremediation. Halides, azide, cyanide, and hydroxide, except for iodide, inhibit activity. In addition, they are sensitive to the amount of nitrogen (Arregui et al. 2019).

Laccase, a part of the multi-copper oxidizing enzyme family, utilizes a non-specific free radical mechanism to break down xenobiotics like azo dyes. Among enzymes, fungal laccase stands out not only because of its high redox potential but also because of its specific advantage over its bacterial counterparts and other enzymes. Unlike other oxidases, laccase can degrade dyes into phenolic compounds, instead of generating toxic amines. Proven sources of highly effective laccase include Trametes versicolor, T. villoa, Cladospora cladosporioides, and Fusarium soloni (Goud et al. 2020; Brazkova et al. 2022). Magalhães et al. (2024) summarized the laccase catalytic mechanisms of different types of dyes (azo, triphenylmethane, anthraquinone, and indigo dyes) (Magalhães et al. 2024). Some dyes whose biodegradation is catalyzed by laccase include Congo red (Si et al. 2013), methyl orange (Navas et al. 2020; Patel Jay et al. 2023), methyl, methoxy, chloro, and nitro substituted phenolic azo dyes (Chivukula & Renganathan 1995; Ngo & Tischler 2022), and malachite green (MG) (Yang et al. 2015; Zhuo et al. 2019; Morsy et al. 2020), Remazol Brilliant Blue R (Osma et al. 2010; Zhuo et al. 2019), and indigo carmine (Campos et al. 2001). The degradation pathway depends on multiple factors, including the structure of the dye and the positions of the different functional groups. Laccases can biodegrade different dyes either via direct oxidation or with the help of redox mediators (Magalhães et al. 2024).

With a molecular weight of 38–48 kDa and roughly 343 amino acid residues, LiP, also known as diaryl propane peroxidase or ligninase I, is a glycosylated monomeric heme protein with a wide range of isoelectric points (3.2–4.7) (Biko et al. 2020). In the presence of H₂O₂, it also exhibits a high redox potential (approximately 1.2 V at pH 3), which permits the oxidation of a variety of aromatic and non-phenolic compounds with or without mediators (Datta et al. 2017). Owing to its effectiveness in removing lignin from lignocellulosic biomass, LiP is also active in delignification and lignin depolymerization (Sharma et al. 2020). In contrast to traditional peroxidases, LiP acts exclusively on aromatic substrates that have already been activated, whereas LiP oxidizes only aromatic rings that have been activated by electron-donating substrates (Singh et al. 2021). The oxidation of veratryl alcohol (VA; 3,4 dimethoxybenzyl alcohol) was used as a cofactor to determine the enzymatic activity (Houtman et al. 2018). This is thought to be a naturally occurring phenolic LiP substrate released in vivo by P. chrysosporium, which functions as a diffusible redox mediator to oxidize the inaccessible substrates into cationic radical species (VA⁺) (Wan et al. 2022). Electrostatic forces maintain this cation on the surface of the enzyme and the presence of VA increases the biodegradation activity of LiP on various substrates (Romero et al. 2019).

In the biodegradation pathway of sulfonated azo dyes, the LiP enzyme is first oxidized using H₂O₂. Subsequently, this oxidized form of LiP catalyzes the oxidation of target xenobiotic compounds such as sulfonated azo dyes. Once oxidized, LiP directly facilitates the oxidation of target dyes (Goud et al. 2020). The biodegradation of the sulfonated monoazo dye (Methyl Orange) by LiP in the presence of H₂O₂ results in two cleavage sites on the chromophore of the azo dye molecule, leading to either asymmetric or symmetric cleavage (McMullan et al. 2001; Goud et al. 2020).

MnP belongs to a class of oxidoreductases (EC 1.11.1.13) and is an extracellular glycosylated protein with molecular weights ranging from 32 to 62.5 kDa (Vasina et al. 2017). The first MnP was discovered in Phanerochaete chrysosporium in the mid-1980s (Glenn et al. 1986). MnP requires a heme prosthetic group as a cofactor and employs H₂O₂ as an oxidant to convert Mn²⁺ to Mn³⁺ (Brazkova et al. 2022). H₂O₂ entered the active sites of MnP during the initial phase of catalysis. An iron peroxide complex is created when the oxygen atom of H₂O₂ bonds to Fe³⁺ in the heme cofactor.

Despite the instability of Mn³⁺ in solution, it can be stabilized by creating a chelate with carboxylic acids, such as malonate, oxalate, oxaloacetate, malate, and even organic acids produced by the oxidation of glucose or cellobiose (Lin et al. 2018). In addition, Mn³⁺-acid chelates have a larger redox potential than free Mn³⁺ and can cross the lignocellulose barrier, which helps accelerate the breakdown of resistant non-phenolic lignin. Ascorbic acid and NaN₃ inhibit MnP, whereas glutathione (GSH) and unsaturated fatty acids, including Tween 80, increase MnP by creating highly reactive sulfur and peroxyl radicals, respectively (Qin et al. 2017). These radicals may travel far, pass through lignocellulose, and attack non-phenolic lignin-like Mn³⁺-acid chelates. For instance, GSH promotes oxidation of the benzyl methyl group in the model dimer molecule VA and non-phenolic lignin, which breaks the ether bond. It is an intriguing contender for biotechnological applications in various industries because of its wide range of substrate-oxidizing capabilities (Sato et al. 2020).

MnP plays a pivotal role in catalyzing the breakdown of complex dye molecules through oxidative reactions (Chang et al. 2021). This process generates highly reactive intermediates that can efficiently biodegrade a wide range of synthetic dyes, thereby rendering them less harmful to the environment (Brazkova et al. 2022). The use of MnP in dye biodegradation processes holds promise for addressing the challenges associated with the persistence and toxicity of synthetic dyes that are extensively used in various industries.

A hybrid of LiP, MnP, and VP is a heme-containing peroxidase. Both VA and Mn²⁺ can be oxidized by VP using a method similar to that of MnP and LiP, because it has two active sites (Zhuo & Fan 2021). Azo dyes, polycyclic aromatic hydrocarbons (PAHs), high-molecular-weight aromatics, phenolic and non-phenolic chemicals, and environmental contaminants can all be oxidized by VPs (Knop et al. 2016). Several species of WRF, such as Pleurotus sp. and Bjerkandera sp., produce VPs; however, they are less prevalent than MnP and LiP (Li et al. 2020).

Assessment of textile dye biodegradation efficiencies among various strains and their associated LEs is crucial for sustainable environmental practices (Thiruppathi et al. 2021). Several fungal, bacterial, and yeast strains and their associated LEs have achieved different dye removal efficiencies, as studied by different researchers. The following subsections are organized based on the types of microbial strains and their associated LEs involved in the biodegradation of a particular dye. During dye biodegradation using an LE-producing strain, more than one type of LEs can be involved or a single strain/LEs can be used. The involvement during biodegradation might be equal, or there might be dominance among the types of LEs. Previous findings were compiled and tabulated with corresponding efficiencies, together with critical parameters such as optimum pH, temperature, and culture/degradation time, underscoring the intricate interplay between microbial strains or their enzymes and biodegradation of textile dyes.

WRF are obligatory aerobes that comprise many basidiomycetes and a few ascomycetes. They are the dominant fungi used for dye biodegradation and produce various LEs (Pan et al. 2017). WRF is central to the global carbon cycle because of its ability to mineralize lignin-containing woody materials with a complex polymeric structure. The ability of these fungi to degrade a range of organic compounds results from the relatively non-specific nature of their LEs, such as LiP, MnP, and laccase (McMullan et al. 2001; Alam et al. 2023). The most widely studied WRF include T. versicolor, Trametes flavida, Trametes hirsuta, P. chrysosporium, and Pleurostus osreatus (Batista-García et al. 2017; Alam et al. 2023; Sharma et al. 2023). A. niger, S. racemosum, P. citrinum, and A. flavus were able to adsorb methylene blue (MB). These results are promising because MB is highly stable (Luo et al. 2022). Rhodamine B (RB) dye uptake was seen in the fungi; A. niger, S. racemosum, P. citrinum, and A. flavus. However, RB has not been decolorized by T. versicolor because of its toxicity and strong chemical structure (Brenk & Wösten 2021).

Table 1 summarizes the various WRF strains and/or their associated LEs biodegradation efficiencies of textile dyes and the optimum values of different parameters affecting dye biodegradation. T. versicolor CBR43 strain was employed for the biodegradation of several dyes (acid dyes (red 114, blue 62, and black 172), reactive dyes (red 120, blue 4, orange 16, and black 5), and disperse dyes (red 1, orange 3, and black 1)). More than 90% of the acid and reactive dyes were obtained using this strain within six days. The decolorization efficiencies for different dyes were 51–80% within 9 days. Laccase is the dominant LE involved in biodegradation. The highest dye degradation rate (97.21%) was observed when T. versicolor IBL-04 was used to biodegrade Remazol Brilliant Yellow-3GL at pH 4 (Asgher et al. 2016). However, another study reported relatively low biodegradation efficiencies for Reactive Blue 19 and Acid Orange 7 (AO 7) (40 and 32%, respectively), using the same strain associated with natural laccase enzymes. However, the efficiency improved to 72 and 80% when Vault-encapsulated laccase was used (Gao et al. 2022). Similarly, only 67% of AO7 was biodegraded by T. versicolor CBR43 within 9 days and laccase and MnP enzymes were the dominant enzymes involved in biodegradation.

In another study, the biodegradation of three azo dyes, reactive black 5 (RB5), acid blue 113 (AB113), and AO7 was studied using an immobilized fungus Trametes hirsuta D7, and only 30% of AO7 was biodegraded. However, biodegradation efficiencies of 92% for RB5 and 97% for AB113 was achieved using the same strain (Alam et al. 2023). These results clearly show that the efficiency of dye biodegradation depends on the type of dye used. Moreover, poor removal efficiencies (<50%) were reported for Xylidine, Poly R-478, and remazol brilliant blue R dyes in laccase-producing T. versicolor, F. antarcticus, and Fomes sclerodermeus (Levin et al. 2004). In another study, the removal ability of T. versicolor WH21 was investigated after treatment with a mixture of Azure B dye and sulfacetamide (SCT). The decolorization of Azure B (300 mg/L) was significantly enhanced from 30.5 to 86.5% within 7 days with the addition of SCT (30 mg/L). Transcriptomic and biochemical examinations revealed that the lignin-degrading enzyme system became active because of the increased enzymatic activity of MnPs and laccase in strain WH21. This activation leads to higher levels of extracellular H₂O₂ and organic acids in response to SCT stress. The purified MnP (more dominant than laccase) and laccase from strain WH21 exhibited significant biodegradation effects on both Azure B and SCT (Zhang et al. 2023).

The use of MnP in dye biodegradation processes is promising for addressing the challenges associated with the persistence and toxicity of synthetic dyes. The MnP enzyme secreted by the Peniophora sp. The CBMAI 1063 strain achieved 94% decolorization of Reactive black 5 (RB5) dye within 168 h. Laccase is also involved in biodegradation, with lower activity than that of MnP (Bonugli-Santos et al. 2016). Another MnP-producing strain (P. chrysosporium) achieved similar biodegradation efficiency (95%) within a short time (48 h) to degrade RB5. However, basic blue 41 was poorly biodegraded (<30%) upon treatment with P. chrysosporium BKM-F-1767 (Contreras et al. 2012). In another study, high-value oxidative enzymes were produced by Cyathus bulleri on agri-food waste for application in Reactive Orange (RO) 16 dye decoloration. High activity of MnP (16.11 ± 1.43 U/mL), laccase (12 U/mL), and aryl-alcohol oxidase (1.25 U/mL) were obtained on the potato peelings (PP) on the 12th day of growth. More than 90% of RO dye was removed within 96 h at pH 4 and 30 °C (Afreen & Mishra 2023).

The LiP enzyme extracted from the WRF also plays a dominant role in the breakdown of various textile dyes. Sosa-Martínez et al. (2020) reported that the decolorization of methyl green by P. chrysosporium CDBB 686 was most pronounced by LiP after 6 h (Sosa-Martínez et al. 2020). They reported a methyl green (50 ppm dye concentration) removal efficiency of 69.79% within 30 h. However, only 41.84% of Congo red was removed by the same strain (Sosa-Martínez et al. 2020). This result indicates that dye biodegradation depends on its structure. In another study, high activities of LiP and MnP were reported by incorporating CuSO₄ and wheat bran as inducers in the decoloration study of Remazol Brilliant Blue R (RBBR) by three basidiomycetes, Tinctoporellus sp. CBMAI 1061, Marasmiellus sp. CBMAI 1062, and Peniophora sp. CBMAI 1063. Complete decolorization was achieved by all strains (Bonugli-Santos et al. 2012).

VP, MnP, and LiP have been reported to be involved in the biodegradation of Remazol Brilliant Blue R dye by Emmia latemargina (MAP03). Complete decolorization was achieved by this strain, but with a relatively longer time (24 days) (Juárez-Hernández et al. 2021). Similarly, laccase, LiP, and MnP produced from fungal mycelia 1TK have been observed to contribute to the biodegradation of MG and MB using sawdust as a co-substrate (Kheirkhah et al. 2020).

In addition to the wider applications of WRF, other fungal strains have been studied for the biodegradation of textile dyes and other pollutants. Several research findings have been reported on the fungal strains involved in textile dye biodegradation, as tabulated in Table 2. Laccase-producing fungal strains can break down aromatic molecules during secondary metabolism (Bhuvaneswari et al. 2020), and the capacity of endophytic fungi associated with mangroves to decolorize aromatic dyes in solid media has been assessed (Obanan et al. 2022). The dye's fading or disappearance from the solid media suggested that fungus mycelia had absorbed it. Aspergillus niger, a fungal endophyte, showed the maximum dye adsorption of all the species tested for their capacity to decolorize, as indicated by the change and disappearance of the red color in the solid medium and the adsorption of dye. All the studied fungal endophytes had Congo red biosorption abilities. Despite their cytotoxic and antifungal characteristics, A. niger, Aspergillus sp., S. racemosum, and Mycelia sterilia adsorb and decolorize MG (Zhou et al. 2019).

The biodegradation efficiency of the fungal strain Lentinus squarrosulus AF5 and its associated LEs (LiP, MnP, and laccase) was investigated. An impressive biodegradation efficiency (93%) was reported for a mixture of textile dyes containing Amido Black 10 B, Reactive Black 5, and Reactive Blue 160 at an optimum pH of 7, a temperature of 25–35 °C, and 72 h. Notable levels of MnP (258.84 ± 0.001 U/mL) along with relatively lower levels of LiP (194.98 ± 0.002 U/mL) and laccase (134.33 ± 0.007 U/mL) were detected during the biodegradation of a mixture of dyes, suggesting thereby the extracellular peroxidases displaying a crucial role in biodegradation process (Mathur et al. 2023). Similarly, laccase-, LiP-, and MnP-producing Ascomycota fungal strain Pseudocochliobolus verruculosus LSF9 was found to biodegrade the yellow 2 dye (Nikam et al. 2017). In this study, 98% of the dye was removed within 7 days.

Moreover, the involvement of LiP in the biodegradation of indigo carmine by fungal strains of T. atroviride has been reported. The biodegradation percentage of the dye was in the range of 93–97% (Lisboa et al. 2017). However, some of the other dyes had poor biodegradation efficiency (<50%), including RB treated with P. citrinum, M. sterilia, and A. flavus (Obanan et al. 2022), Direct Black 38, and Direct Black 22 treated with Echinodontium taxodii EF422215 (Han et al. 2014). Generally, synergetic effects of laccase, LiP, and MnP are observed during biodegradation.

A real textile effluent was decolorized using suspended and immobilized Geotrichum candidum fungus and achieved removal efficiencies of 85.5 and 98.5%, respectively, within 6 h, with optimized parameters, such as inoculum size (5%), pH of 4.5, and temperature of 30 °C. High levels of laccase 22 and 25 U/L during suspended and immobilized fungal cell treatment, respectively, were observed during decolorization and were found to be directly proportional to laccase activity (Rajhans et al. 2021). Enzyme immobilization is very important for the effective utilization of enzymes in dye biodegradation. Decolorization was assessed using Allura Red AC dye through free and immobilized laccase extracted from Trametes pubescens. The decolorization of Allura Red AC by free and immobilized laccase was 68.4 and 4.6%, respectively, indicating that although enzyme stability was improved, dye decolorization was negatively affected. The lower efficiency of immobilized laccase can be attributed to steric hindrance, mass transfer limitations, or the absence of mediators in the immobilization matrix (Mejía-Otálvaro et al. 2021).

Moreover, LEs from several fungal species have been heterologously produced in Escherichia coli to increase enzymatic activity and biodegradation (Xu et al. 2020) and in Pichia pastoris (Csarman et al. 2021). For instance, a study reported that expression of the laccase gene from Trametes trogii in P. pastoris resulted in the production of thermostable recombinant laccase, which has a half-life of 45 min at 70 °C and can decolorize azo dyes such as Acid Red 26 (Huang et al. 2020). Similarly, a study reported that P. pastoris expresses laccase from Trametes sp. 48424, resulting in a high output of recombinant laccase and an ability of the enzyme to decolorize various dyes (Wang et al. 2017). The results revealed the importance of applying immobilization techniques and recombinant technologies to enhance biodegradation efficiency.

Bacterial strains play important roles in dye biodegradation. Several bacterial strains can produce LEs, which can break down chemical bonds in dyes and biodegrade them into simpler compounds. According to the hypotheses of different studies, co-metabolic responses among members of a microbial community may imply efficient mineralization and biodegradation of the dye pollutants. A co-culture of bacteria can cooperate with a range of hue and pigment combinations. This consortium works well, because a single strain can attack and biotransform dye molecules. Over time, bioconverted dyes have become more readily accessible to various bacterial strains and their associated LEs (Thiruppathi et al. 2021). Table 3 summarizes the various microbial strains and their associated laccase enzyme biodegradation efficiencies for different textile dyes. A LiP enzyme-producing bacterium (Bacillus albus) was isolated from textile wastewater and sludge samples. This bacterium decolorized 99.27% of the MB dye (100 mg/L) and removed 83.87% of COD within 6 h at 30 °C and pH 7. The LiP enzyme produced had a molecular weight of ∼48 kDa, as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis (Kishor et al. 2021). In another study, a lignin-degrading bacterial isolate, L15, was found in decaying wood samples and was utilized for the decoloration of Azure B (100 mg/L). A decoloration percentage of 90% was achieved within 24 h by this strain, and laccase was the dominant LE involved in its biodegradation (Kaur & Sharma 2022). A relatively low biodegradation efficiency (62%) of Azure B and phenol red (250 mg/L) was reported for laccase- and MnP-producing Bacillus cereus strains, even after an extended biodegradation time (72 h) (Kumar et al. 2022). Similarly, only 72% of the Azure B dye was degraded by the LiP-producing strain Serratia liquefaciens LD-5 after 144 h (Haq et al. 2016).

In some studies, different LEs have contributed to the synergetic biodegradation of a particular dye. LiP, MnP, and laccase contributed equally to dye biodegradation (Table 3). For example, laccase and MnP are key enzymes involved in the biodegradation of MB by the bacterial strain Bacillus thuringiensis F5. Strain-derived laccase and MnP enzymes for MB biodegradation had an efficiency of 89.6% at 30 °C within 12 h (Wu et al. 2022). Another bacterial strain, Bacillus paramycoides strain K7.2, was isolated from soil samples and used for the biodegradation of a variety of azo dyes such as Congo red (CR), MB, Alizarin Red S (AR), and Remazol Brilliant Blue R (RBBR). The isolate produced laccase, LiP, MnP, and other enzymes that can decolorize dyes, and 82.79% of the CR dye was decolorized after 7 days of incubation at an optimal pH of 7 (Rahayu et al. 2023). LiP and laccase are key enzymes that contribute to the decolorization of Metanil Yellow G by the halophilic alkali thermophilic bacterial consortium ZSY over a wide range of pH values (8–10), temperatures (40–50 °C), dye concentrations (100–400 mg/L), and salinity levels (1–10%) (Guo et al. 2020).

Some microalgae species have also resulted in promising biodegradation of dyes. Seven microalgae isolates such as Nostoc muscorum, Nostoc humifusum, Spirulina platensis, Anabaena oryzae, Wollea saccata, Oscillatoria sp., and Chlorella vulgaris were investigated for dye decolorization. C. vulgaris achieved the highest biodegradation of Brazilwood, Orange G, and Naphthol Green B dyes (99.5, 99.5, and 98.5%, respectively). In contrast, A. oryzae achieved the maximum removal efficiency for crystal violet (CV) (97.4%), and W. saccata removed 93.3% of the MG. The enzyme activity assay revealed that the highest laccase production was recorded by C. vulgaris with Brazilwood, Orange G, and Naphthol Green B dyes (665.0, 678.6, and 659.5 U/mL, respectively). Similarly, C. vulgaris gave a high LiP enzyme production with the above three dyes (306.00, 298.34, and 311.45 U/mL), respectively. In addition, A. oryzae and W. saccata exhibited the highest production of the laccase enzyme (634.6 and 577.45 U/mL, respectively) with CV and MG dyes. Moreover, C. vulgaris, A. oryzae, and W. saccata have been suggested as candidates for bioremediation and preprocessing to remove dyes from textile effluents (Abd Ellatif et al. 2021).

The yeast isolate Meyerozyma caribbica was also decolorized with various dyes, including AO7, with efficiencies ranging from 87.2 to 98.8%. The strain exhibited high levels of extracellular MnP activity, ranging from 23 to 27 U/mL. Almost complete decolorization was achieved by this MnP-producing strain after 6 h of incubation with 50 mg/L of the sulfonated azo dye AO7 at 28 °C with an agitation speed of 150 rpm. Moreover, the maximum decolorization efficiency of AO7 is 93.8% at 400 mg/L (Ali et al. 2022). Most of the aforementioned results indicate that the biodegradation efficiency strongly depends on the type of strain used and other parameters. A suitable LEs-producing strain, along with critical parameters such as optimum pH, temperature, and culture/degradation time, should be selected for the effective degradation of dyes.

The factors mentioned in the preceding sections indicate that both intracellular and extracellular enzyme activities are significantly affected by the type of strain used, temperature, pH, pollutant bioavailability, nutrient type and concentration, enzyme concentration, and agitation (mixing). Therefore, achieving effective biodegradation of dyes in both lab-scale and industrial applications requires the selection of a suitable LE-producing strain and optimization of key parameters.

Different microbial enzymes can biodegrade environmental contaminants, including dyes, at different temperatures, and effective biodegradation can be achieved at the optimum enzymatic activity at the optimum temperature. Since enzymes are proteins, they are especially susceptible to high temperatures, which may cause the protein to become denatured or change its 3-dimensional structure. The optimal temperature range for Stropharia aeruginosa to biodegrade synthetic Alizarin Cyanine Green dye was found to be from 20 to 40 °C because laccase enzymes become inactive or cleaved at higher temperatures (Agrawal & Verma 2019). The greatest deterioration of 100% was observed at 40 °C. Navada et al. (2018) determined the optimal operating temperature range (25–45 °C) for anthraquinone dye biodegradation (Navada et al. 2018). The identical laccase enzyme, however, performed best in some species at 50 °C. The optimal temperature range for peroxidases was 15–30 °C (Lopes et al. 2020).

Different enzymes generated from various microbes have different optimum pH values. The pH value decreased enzyme activity beyond the optimal value. Most enzymes function optimally in the neutral pH range. An investigation was conducted on the biodegradation of synthetic dyes, such as methyl green, Congo red, and Poly R-478, using LEs produced from fungal species, such as LiP and MnP (Sosa-martínez et al. 2020). The optimal pH for biodegradation of unpurified enzymes was between 7 and 8. In contrast, the optimal pH range for purified MnP was 4–5. This difference in pH may be explained by the involvement of several enzymes (Sosa-martínez et al. 2020). For example, in an investigation on the ability of T. versicolor IBL-04 to biodegrade Remazol Brilliant Yellow-3GL, a medium with a pH of 4 showed the highest rate of dye biodegradation (97.21%), followed by pH values of 3.5, 3, 4.5, and 5, with dye biodegradation rates of 72.66, 63.75, 49.31, and 40.81%, respectively (Asgher et al. 2016). The optimal pH should be determined based on the components of the medium and composition of the dye components (Lu et al. 2017).

The number of pollutants readily assimilated by microorganisms and available for biodegradation is referred to as bioavailability. The amount of pollutants present in aqueous media has a significant impact on enzyme-mediated bioremediation (Mwanza 2017). A new alkaline protease enzyme isolated from Bacillus cereus KM201428 was used to study the biodegradation of the pigment MG. The experiments were conducted with MG dye concentrations ranging from 0.93 to 9.30 mg/L. Owing to the increased number of dye molecules available for biodegradation, the efficiency increased with increasing MG dye concentration (Mwanza 2017). However, above a certain limit, increasing the dye concentration negatively affects the activity of microorganisms (Dao et al. 2021).

The large-scale production of fungal enzymes is thought to be limited by the amount of carbon (Agrawal et al. 2018). The amount of carbon present in a lignocellulosic substrate and nutritional medium influences enzyme production (Metreveli et al. 2021). According to Zheng et al. (2017), Trametes pubescens began producing laccase when glucose concentration in the growth medium was very low (Zheng et al. 2017). High laccase activity was observed when T. pubescens quickly and efficiently metabolized cellobiose and glucose (Schneider et al. 2018). Laccase activity is higher in Pleurotus sajorcaju cultures grown in glucose media than in lactose-based cultures (Diaz-Godinez et al. 2017). Conversely, lactose appeared to be the best carbon source for Pseudotrametes gibbosa laccase production and was beneficial for Cerrena unicolor and Fomes fomentarius enzyme secretion. Furthermore, these three fungi significantly increase the amount of laccase in glycerol (Schneider et al. 2018).

Several researchers have increased enzyme activity using bran, sawdust, or wheat straw as substrates (Elisashvili et al. 2018). Mandarin peels and grapevine sawdust were shown to be the most effective medium carbon sources for achieving maximum laccase activity in Pleurotus eryngii and Pleurotus ostreatus (Zhu et al. 2016). When wood was used as a carbon source and milled alder was used as an inducer, the maximum LiP activity and discernible levels of MnP were observed. The highest MnP activity was observed in pineapple peel cultures (Madadi & Abbas 2017). Using several carbon sources, an attempt was made to achieve the highest dye decolorization efficiency of Stropharia sp. ITCC-8422 at 200 ppm. The use of sucrose indicated that it was an effective carbon source, with 97.4% dye decolorization (Agrawal & Verma 2019). The presence of sucrose causes the greatest degree of decolorization of Malachite Green (Barapatre et al. 2017).

The large-scale production of fungal enzymes is thought to be affected by nitrogen availability (Agrawal et al. 2018). It is commonly recognized that Phanerochaete chrysosporium, the fungus responsible for white rot, can only create LiP and MnP when grown in a synthetic medium with low nitrogen (Zeng et al. 2013). However, it was discovered that high nitrogen content increases enzyme production when a lignocellulosic substrate is present (Yang et al. 2020). Prior research has demonstrated that the type and quantity of nitrogen supply are important nutritional variables that control the release of LEs (Pinheiro et al. 2020).

Many inorganic and organic nitrogen sources have been used to increase enzyme production by G. lucidum (Schneider et al. 2018). The addition of KNO₃ to the culture medium resulted in maximum laccase activity. The same drug only marginally promoted the accumulation of MnP. Thus, peptone appears to be the best nitrogen source for laccase production. Using various nitrogen sources (amino acids, yeast extract, and peptone), L-glutamic acid produced maximum laccase activity in Trametes trogii (Kunjadia et al. 2016).

LiP and MnP enzymes are exclusively produced by Phanerochaete chrysosporium when nutrients are restricted during cultivation. A high nutrient concentration, on the other hand, promoted the synthesis of these enzymes in the presence of a ligninolytic substrate. In the submerged fermentation of wheat bran, several inorganic and organic nutrient sources help G. lucidum produce more enzymes. KNO₃-supplemented culture media showed the highest levels of laccase activity. This substance mildly promotes MnP synthesis (Schneider et al. 2018). Using a yellow laccase-producing strain, Stropharia sp. ITCC-8422, different nitrogen sources were optimized for the decolorization of the synthetic dye Alizarin Cyanine Green. Peptone, beef, and yeast extract produced the highest level of decolorization on the second day. It has been shown that peptone 96.3% is the least effective nitrogen source, whereas malt (98.2%), beef (97.6%), and yeast extract (97.1%) are the most effective (Agrawal & Verma 2019).

In addition to natural inducers, synthetic inducers can also be used to increase enzyme activity. The addition of the aromatic chemical 2,5-xylidine has been shown to increase laccase activity in WRF (Metreveli et al. 2021). The administration of various aromatic compounds, such as guaiacol, 1-HBT, ferulic acid, and VA, increases laccase secretion (An et al. 2020). Ferulic acid has been employed to induce maximal laccase activity (Kuhar & Papinutti 2014; Wang et al. 2014).

Tween 80 was used to increase MnP activity (Dao et al. 2019). P. chrysosporium produces the highest MnP activity when Tween 80 is added (Munir et al. 2015). Tween 80 was also found to increase the synthesis of LEs released by Stereum ostrea (An et al. 2018). After studying P. eryngii laccase in an ammonium-tartrate-containing glucose medium, the isolates produced isoenzymes exhibiting laccase activity (Muñoz et al. 1997).

Certain solvents can be used to dissolve compounds that are insoluble in water, and their activities as enzyme inducers can be studied. For instance, ethanol or dimethyl sulfoxide is frequently employed as a solvent to dissolve substances that are insoluble in water to measure enzyme activity. However, ethanol is also employed as an active solvent to stimulate enzyme activity (Skočaj et al. 2018). The laccase activity of T. versicolor was enhanced when ethanol was added to a solution containing glucose as the carbon source. Additionally, ethanol had a mediating influence on laccase synthesis in Coriolus hirsutus and Grifola frondosa (Wang et al. 2014).

While certain heavy metals are required by fungi, others are not, and when present in excess, they can be harmful (Rodríguez-Couto 2017). Typically, a few times the required concentration of metals is required to become poisonous (Aljerf & AlMasri 2018). Copper, iron, zinc, nickel, manganese, and molybdenum are required by fungi. Silver, mercury, cadmium, chromium, and lead are non-essential metals (Meier et al. 2012).

Manganese and copper are the two most significant metals in the WRF. Manganese has been shown to regulate the expression of LiP, MnP, Laccase, and the breakdown of lignin (Gadd et al. 2014). Copper is a cofactor in laccase catalytic centers. In Pleurotus ostreatus, optimized culture media containing lignin and Cu²⁺ induced laccase secretion (An et al. 2018).

The beneficial synergistic interaction between lignin and Cu²⁺ led to a 60-fold increase in the activity. Numerous laccase genes have also been shown to contain metal-responsive elements (Priyadarshini et al. 2021), which may account for the beneficial effects of copper ions on laccase levels. Vrsanska et al. (2016) reported that Pleurotus ostreatus cultures supplemented with Cu²⁺ secreted more laccase isoenzymes than usual (Vrsanska et al. 2016). This outcome is comparable to that reported by (Rodrigues et al. 2019), who observed elevated laccase activity following Cu²⁺ supplementation. Although the existence of copper in the catalytic center of the enzyme has long been recognized, research on the regulation of its role in laccase production is relatively new (Priyadarshini et al. 2021). Several studies have examined the beneficial effects of metal-ion addition on enzyme synthesis (Yang et al. 2020). Moreover, laccase stimulation has been investigated using various metals, which can result in oxidative stress in T. pubescens. For instance, the activity of laccase produced by Pleurotus ostreatus was enhanced when 1–5 mM Cd was added (Zhu et al. 2016).

Since extracellular enzymes are not shielded by the cell-associated metal detoxification system, they must deal with large quantities of metals. Metals can affect the transcriptional and translational regulatory levels by influencing the synthesis of extracellular enzymes within the cell (Priyadarshini et al. 2021). The growth of the LE system requires modest quantities of critical heavy metals (Zhang et al. 2021). The activities of LiP and MnP in P. chrysosporium were enhanced by the addition of small amounts of Cu and Zn to a metal-free synthetic culture medium (Zhang et al. 2021).

The enzyme dosage used in the biodegradation process plays a crucial role in bioremediation of pollutants including dyes. Typically, biodegradation efficiency increases to a certain point with increasing enzyme concentration. Thus, it remained persistent because of the limited concentration of pollutants in the batch system (Al-dhabi et al. 2020), which tested the ability of MnP from Bacillus velezensis to biodegrade tetracycline. Inoculum doses of MnP enzyme ranging from 1 to 11% (w/v) were used in batch studies. The optimal inoculum size for achieving higher biodegradation efficiency was 7% (w/v). Additionally, owing to the microbial co-metabolism for pollutant cleanup, increased biodegradation has been achieved using dilute enzyme solutions (Al-dhabi et al. 2020).

Because agitation is primarily responsible for the transmission of heat, substrate, and oxygen during the process, it is also regarded as a critical factor for the bioremediation of contaminants. Due to improved oxygen availability during aerobic processes, increased agitation speed leads to increased biodegradation efficiency. Enhanced tetracycline biodegradation potential was observed at 200 rpm (Al-dhabi et al. 2020). Mediators are small compounds that enzymes can readily oxidize. The mediators raise the redox potential and electron shuttle, which improves the enzyme's catalytic activity. To test the biodegradation of organic contaminants, syringaldehyde (SA) and 1-hydroxy benzotriazole (HBT) at concentrations of 0.1, 0.5, and 1 mM were evaluated using crude enzyme extracts from Trametes versicolor. In both cases, the optimum mediator concentration (0.5 mM) was superior because excessive mediator concentrations caused the enzyme-mediator system to produce free radicals that reduced enzyme activity (Saravanan et al. 2021).

LEs have several industrial applications and are of substantial economic importance for food processing, cosmetics, pharmaceuticals, pulp, textiles, detergents, and biofuel production (Othman et al. 2023). For example, laccase has potential applications in pulp and paper industries because of its oxidation, decarboxylation, substrate demethylation, lignin depolymerization, and kraft pulp (Singh & Arya 2019). In addition, laccase can be used in food processing to enhance the color of food and eliminate unwanted phenolic substances (Mayolo-Deloisa et al. 2020). In addition to laccase, LiPs, and MnPs have potential applications in the production of aromatic flavors in food and beverage industries. Moreover, LiP and MnP are potential enzymes for contaminant removal from pulp paper mill wastewater (Kumar et al. 2022). They can oxidize substrates in the presence of H₂O₂ and Mn²⁺ to biodegrade halogenated phenolic compounds, PAHs, and other aromatic compounds. The three most important enzymes (lactase, LiPs, and MnPs) play crucial roles in the manufacture of medical and pharmaceutical products and polymer production (Debnath & Saha 2020). Furthermore, LEs are important for the depolymerization of lignocellulosic biomass into value-added simple products such as chemicals, biofuels, animal feeds, and enzymes (Kumar & Chandra 2020).

Although LEs have different applications, they are obtained from different sources and play key roles in pollutant biodegradation; however, they have several limitations. LEs for the bio-bleaching process in the pulp paper industry have faced several challenges, such as large-scale production, uneconomical mediators, stability, and accessibility (Morsy et al. 2020). Beyond these difficulties, some of the redox potentials of LEs and their suitable substrates restrict their commercialization. Thus, these challenges have attracted research in this area, focusing on the production and process optimization of technologies to alleviate the aforementioned problems. Moreover, the available literature on the characteristics of LEs, especially their chemical properties, mechanisms, and actions, is scattered, limiting the knowledge and its application. For instance, it has been reported that lignin can be biodegraded by LEs produced by fungi, but their large-scale growth has not been successful, possibly because of environmental conditions such as pH and temperature (Basu et al. 2015). Most fungi grow under acidophilic conditions and require a semisolid fermentation process. For instance, laccase extracted from Trametes versicolor grows optimally at pH 3 (Suryadi et al. 2022). Therefore, inefficient growth can occur if these enzymes are extracted from environmental samples that are alkaline, such as pulp and paper, textiles, and detergents.

Some LEs, such as laccase, have low redox potentials, which can result in the limited biodegradation capacity of lignin. In this case, mediators are required to overcome this limitation and enhance the redox potential of laccase; they can properly diffuse into the biomass fiber part (Munk et al. 2018). Not all species produce LiP or MnP; rather, they only produce laccase for lignin biodegradation (Majumdar et al. 2014). In addition, reports assured that single LEs did not act on biodegradation, but multiple other enzymes, such as feruloyl esterase, aryl-alcohol oxidase, quinone reductases, and several mediators, cooperatively facilitated this process (Andlar et al. 2018). Biomass containing lignocellulose has a strong binding tendency, which results in inhibition of enzymatic activity. Thus, improvements in the development of environmentally friendly approaches for biodegradation of intermediate lignocellulosic materials are currently an active research topic.

The feasibility of enzyme utilization in real-world applications may vary and is challenging. In addition to the utilization of enzymes, advanced biological treatment technologies are gaining attention for treating textile dye wastewater. These treatment technologies, such as aerobic, and anaerobic, and integrated more than one reactor condition (anaerobic/aerobic or aerobic/anaerobic) biological treatment processes. They offer advantages such as high efficiency, low energy consumption, and reduced chemical usage, making them options for sustainable wastewater treatment in the textile industry. Therefore, advanced biological treatment technologies can benefit the treatment process where oxidoreductive enzymes are involved, thereby effectively degrading textile dyes.

Scholars agree that biological processes do not produce dangerous substances after dye biodegradation, as long as effective techniques and efficient microorganisms are used, and experimental conditions are optimized and are thought to be feasible compared to physiochemical processes (Bhatt et al. 2021; Mishra et al. 2021). However, conventional biological treatment processes, called activated sludge processes, are mostly single-reactor processes that have limitations in the treatment of textile dyes. For instance, if the treatment process is employed only under anaerobic reactor conditions, the reduction of azo dyes by azoreductase produces toxic intermediates such as aromatic amines. Hence, integrated aerobic reactor conditions are required to further oxidize the anaerobically treated effluent. Oxidative enzymes (ligninolytic or non-ligninolytic) are important enzymes that are mostly produced by aerobes under aerobic conditions. These conditions and enzymes are important for minimizing dye-transformed intermediate substances by oxidizing them to low-molecular-weight non-toxic organic acids and further mineralization to carbon dioxide and water. Therefore, advanced biological treatment technologies that integrate anaerobic and aerobic reactor conditions for the biological treatment of textile industry wastewater are critical to alleviate this problem. The development of this advanced technology has recently attracted increasing attention because the potential of anaerobes first reduces organic loads by decolorizing intense dye colors and then aerobes further biodegraded substances, making it effective for the complete dye biodegradation process (Samuchiwal et al. 2023; Bogale et al. 2024). Moreover, this treatment approach has also been used in combination with other physicochemical treatment technologies, such as membrane filtration (Khosravi et al. 2020; Ramesh et al. 2021) and adsorption using novel adsorbents (such as granular activated carbon (GAC)) (Fundneider et al. 2021; Lin & Ho 2022), and oxidation processes (i.e. including ozonation) (Mirza et al. 2020; Jahan et al. 2022) to further increase the effluent quality.

Employing advanced biological treatment technologies for textile industry wastewater on its own is not sufficient for achieving effective results. The biodegradation of dyes, with a reduction-oxidation reaction process, can be conducted using enzymatic or microbial cells (Roy et al. 2018; Bilal et al. 2021). It is important to use adaptive and efficient microorganisms to examine the effectiveness of enzymatic activities in order to make the treatment process effective. These enzymes can be separated from free and immobilized cells (Morsy et al. 2020). Most dye biodegradation processes are catalyzed by intracellular or extracellular enzymatic activity. The extracellular enzymatic biodegradation of textile dyes has been a promising approach over the last few decades (Alsukaibi 2022). Compared with living cell biodegradation, enzymes may target a specific contaminant and can be applied and persist even under harsh and adverse environmental conditions (Bilal et al. 2022). However, scholars have argued that the feasibility of enzyme utilization in real-world applications might vary and could be challenging owing to different enzyme characteristics. Immobilization of cells and/or enzymes on a solid support is one of the most important actions to be taken to increase enzyme efficiency and feasibility for dye biodegradation. Using immobilization techniques, enzymes can react with a wide range of complex compounds, biodegrade quickly, and produce fewer toxic by-products. Immobilizing cells and/or enzymes is economically feasible, as they can be recycled, reused, durable, and sustainable for bioremediation of wastewater containing dyes. However, the efficiency of cells and/or enzymatic biodegradation of dyes depends on several factors and circumstances, such as pH, temperature, agitation, oxygen transfer, inoculum size, redox mediator presence, and dye structure and concentration (Magalhães et al. 2024).

Waste biomass is ubiquitous on Earth, has broad prospects as a substrate for LEs-producing microorganisms, and is a powerful resource for the development of improved enzymatic catalysts. These enzymes are much better at breaking down cellulosic materials than other enzymes are. Lignin's chemical properties are complex and difficult, making it highly resistant to microbial biodegradation, but LEs can undergo its depolymerization process. The ability of LEs to interact with lignin materials makes them capable of biodegrading toxic industrial chemicals such as textile dyes. They have the potential to be alternative enzyme sources for bioremediation of hazardous and toxic chemicals because industrialization produces highly abundant chemical pollutants in the environment. As excess lignocellulosic waste also produces abundant LEs-producing microbes in the environment, bioremediation of toxic substances has boosted the search for these enzymes for use in wastewater management. Future research should focus on identifying, discovering, cloning, and characterizing efficient strains of microorganisms capable of producing LEs for the biodegradation and detoxification of textile dyes. The focus should be on novel biotechnological applications, which are crucial for achieving these objectives.

Although LEs exhibit a better dye biodegradation efficiency than non-LEs, their practical application in industrial dye wastewater is limited. To overcome these limitations, the biocatalytic properties and stability of LEs need to be improved. Immobilization techniques are advisable to improve the properties of cells and/or LEs. In addition, recombinant DNA technology, which enhances the biodegradation efficiency of LEs, is gaining interest. Protein engineering is a pioneering discipline in the application of recombinant DNA technology that involves predetermined changes in amino acid sequences and their biochemically established catalytic mechanisms. This technology can be applied, and the enzymes must be improved and optimized to increase dye biodegradation efficiency. Several protein engineering approaches can be employed for recombinant DNA technology, including directed enzyme evolution and rational, semi-rational, and de novo designs. Thus, these techniques are crucial for effectively modifying enzymes for efficient biodegradation of textile dyes. Furthermore, identifying new microorganisms and their enzymes, as well as employing biotechnological methods for bioremediation of textile wastewater, is of paramount importance. Efficient and sustainable bioremediation of textile wastewater requires the identification of microorganisms and enzymes that can tolerate alkaline conditions, as wastewater is alkaline. Additionally, other issues, such as the mechanisms of biodegradation, impact of microbial responses on the environment, recalcitrant metabolites, and new xenobiotic compounds, need to be thoroughly investigated.

Due to their complex structure and susceptibility to microbial biodegradation, synthetic dyes are classified as persistent organic pollutants that require sustainable, efficient, and environmentally friendly biodegradation methods. The ability of ligninolytic oxidative enzymes to efficiently biodegrade a wide range of textile dyes is an effective approach to the treatment of textile wastewater. The structure of LEs makes them highly stable during biodegradation compared with other enzymes. Laccase, LiP, and MnP are known LEs studied for the biodegradation of textile dyes. Studies have reported that fungal strains, particularly WRF strains, are major sources of LEs and are used for the biodegradation of different textile dyes. Some studies have also shown that bacteria, yeasts, and microalgae species are sources of LEs that are used in dye biodegradation studies. These enzymes have a synergistic effect on dye biodegradation at different dye types and concentrations. They can remove up to 99% of textile dyes by one or more LEs within a wide range of pH and temperature, predominantly from 25 to 37 °C. However, detailed studies with various process parameter optimizations and large-scale studies are limited. Based on the evaluation of the previously mentioned discussion regarding the roles of LEs in the biodegradation of textile dyes, the following conclusions and recommendations were drawn.

• Different LE sources, ranging from prokaryotic to eukaryotic organisms, are promising for accelerating textile dye biodegradation.

• The effectiveness of LEs is influenced by both experimental and environmental factors.

• Most studies have been conducted using simulated textile wastewater.

• It is critical to study the effectiveness of strains and/or LE using real textile wastewater and optimize the experimental conditions.

• Evaluating LEs involvement in dye degradation under aerobic and anaerobic reactor conditions is required.

• It is crucial to evaluate the feasibility, potential, and practicality of large-scale implementations.

The authors thank the institutes/universities affiliated with this study for allowing access to resources. The authors would like to thank the organizations and scholars who have used the previous findings related to this work.

T.A.A. contributed to conceptualization, writing – review & editing, writing – original draft, visualization, methodology, formal analysis, data curation. F.M.B. contributed to writing – review & editing, writing – original draft, visualization, methodology, formal analysis, data curation. E.L.T. contributed to writing – review & editing, visualization, methodology, formal analysis.

This study was not supported by any funding sources.

The authors declare that there are no known competing financial interests or personal relationships that could have influenced the work reported in this study.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.