A new bacterial-derived biosurfactant for biotechnological applications in the oil industry: production, optimization, biosurfactant functional and physicochemical characterization

BioS

biosurfactant

ST

surface tension

ODA

oil dispersion activity

CMC

critical micelle concentration

CCD

central composite design

Water pollution causes great damage to the environment and ecological equilibrium. Petroleum products consisting of aliphatic or aromatic hydrocarbons are the most polluting compounds. They have received special attention in recent years because of their toxic, carcinogenic and mutagenic characteristics (Sharma et al. 2022; Zahed et al. 2022). In pursuit of this aim, numerous physicochemical, biological and combined treatment methods were developed to combat hydrocarbon pollution. Biological decontamination or bioremediation uses the action of microorganisms (bacteria or fungi) to detoxify organic contaminants by complete or partial biodegradation preferentially in situ, and has gained great attention due to the low implementation cost, simplicity and respect for the environment (Sharma et al. 2022; Zahed et al. 2022). Nevertheless, the low solubility and bioavailability of petroleum-derived products in water and soil, respectively, limits their biological treatments (Sharma et al. 2022; Zahed et al. 2022). In fact, they can form a stable oil layer on the surface of the water, tend to agglomerate in water, and adsorb strongly in soil, making them less accessible to attack by microorganisms and difficult to assimilate (Sharma et al. 2022). Therefore, increasing the dissolution of hydrophobic compounds in water and their desorption rates from soil particles are of great interest to enhance their depollution, especially by biodegradation. Furthermore, due to increasing exploitation, production, transportation and storage, oil spreads over a large area on the sea surface, provoking considerable detriment to plants and animals disturbing therefore all the ecological equilibrium (Mnif et al. 2017a). The use of synthetic dispersants, specified as a material that decreases the cohesive attraction between similar particles, is an effective means that facilitates the mechanical recovery of oil spills (Mnif et al. 2017a; Ng et al. 2022)

As known, surfactants defined as amphiphilic compounds with a hydrophilic head and a hydrophobic tail have the ability to reduce the surface tension (ST) of water along with oil dispersing, emulsification and foaming activities (Shaban et al. 2020). They are exploited, among other applications as detergents, emulsifiers, foaming and dispersants agents (Shaban et al. 2020). Most of the surfactants currently used are produced by chemical synthesis and are derived from petrochemical compounds (Shaban et al. 2020). Therefore, they are toxic and non-biodegradable (Shaban et al. 2020). However, interest in microbial surfactants called biosurfactants (BioS) has increased significantly over the past decade (Mnif & Ghribi 2015a, 2015b, 2015c; Fenibo et al. 2019). These BioS are very diverse and quickly biodegradable (Mnif & Ghribi 2015a, 2015b, 2015c; Fenibo et al. 2019). They are well characterized by their great properties to be active under extreme temperature, pH and salt conditions in addition to their stabilities (Mnif & Ghribi 2015a, 2015b, 2015c).

Owing these functional activities and physicochemical properties, BioS are applied in many fields, including the food and chemical industry, pharmaceutics and biomedicine, environment and bioremediation (Carolin et al. 2021; Karlapudi et al. 2018; Nikolova & Gutierrez 2021; Sakthipriya et al. 2021). They have a great interest in their use as an improver of hydrophobic compounds’ solubility in water, mobility from soil particles and as an oil dispersant agent to combat oil spills, enhancer of oil biodegradation (Mnif et al. 2013a, 2013b, 2014, 2015a, 2017b). Thus, permitting their involvement in the water treatment process.

Basically, BioS are produced by multiple varieties of microbial strains during their growth on water-immiscible compounds (Mnif & Ghribi 2015a, 2015b, 2015c; Fenibo et al. 2019). However, their low yield and high-cost production limit their application. The enhancement of the yield of production and the optimization of economic bioprocesses has become of great interest to biotechnologists. It can be achieved by strain improvement by classical or directed mutagenesis, by using recombinant strains and by optimizing the nutritional requirements and physicochemical conditions of fermentation (Mnif & Ghribi 2015b, 2015c). In fact, numerous nutritional parameters can affect BioS production, such as carbon and nitrogen sources as well as mineral elements (Beltran-Gracia et al. 2017; Nurfarahin et al. 2018; Singh et al. 2019). To know, a broad variety of hydrophilic carbon sources, mainly carbohydrates and sugars (Zhang et al. 2016; Ghazala et al. 2017; Hmidet et al. 2017; Phulpoto et al. 2020) and hydrophobic carbon sources, mainly hydrocarbons and vegetable oils (Ndlovu et al. 2017; Ohadi et al. 2017; Patowary et al. 2017) can be exploited to produce BioS. These different carbon sources can be used separately or as mixed substrates (Sarubbo et al. 2016; Joy et al. 2017). However, glucose rests as the primary source for BioS production, as widely recognized (Eswari et al. 2016). However, in addition to glucose, sucrose can be used as an interesting sugar for lipopeptide production (Liu et al. 2012; Singh et al. 2014). Additionally, nitrogen sources can influence greatly BioS production. In pursuit of this aim, various organic or inorganic nitrogen sources can be employed. Well-known organic nitrogen sources like yeast extract, tryptone and glutamic acid can support higher production yields (Eswari et al. 2016; Beltran-Gracia et al. 2017). In addition, other organic nitrogen sources, namely peptone, casein acid as well as soybean flour have been used (Beltran-Gracia et al. 2017). Moreover, ammonium nitrate, ammonium sulfate, sodium nitrate, urea and glutamic sodium were assayed as inorganic nitrogen sources (Beltran-Gracia et al. 2017; Moshtagh et al. 2019; Phulpoto et al. 2020). On the other hand, previous research work denoted the important effect of trace elements, namely magnesium, manganese, iron, copper and nickel on BioS production (Lin et al. 2007; Beltran-Gracia et al. 2017; Bartal et al. 2018). Additionally, physicochemical factors like the initial pH of the culture medium, the incubation temperature as well as the rate of agitation have a great effect on lipopeptide production (Beltran-Gracia et al. 2017; Moshtagh et al. 2019; Phulpoto et al. 2020). For the agitation speed, moderate values in the order of 150–200 rpm can support maximal BioS production (Mnif & Ghribi 2015b, 2015c). For the temperature, lipopeptides production can be accomplished between 25 and 45 °C (Mnif & Ghribi 2015b, 2015c). For the pH, a neutral value is the most favorable for an optimal BioS production (Mnif & Ghribi 2015b, 2015c).

The experimental planning methodology can be applied to optimize nutritional and physicochemical conditions permitting a best BioS production (Mnif & Ghribi 2015a; Bertrand et al. 2018; Fenibo et al. 2019; Moshtagh et al. 2019; Singh et al. 2019; Phulpoto et al. 2020). In pursuit of this aim, we are interested in the present work to produce a new BioS with diverse functional properties derived from a new Bacillus sp. strain. It was isolated from a hydrocarbon-contaminated biotope in the region of Djerba in Tunisia and screened for its ability to reduce the ST of the culture medium along with its hemolytic activity. Microscopic observation and biochemical characterization by API 50 CH (Biomérieux; API Reference Guide) showed that the strain is Gram-positive isolate belonging to the Bacillus genera. As characterized in our previous work, Bacillus sp. MI27 produced lipopeptide isoforms belonging to the cyclic and linear surfactin families. The m/z values of the cyclic homologs of surfactin were about 994; 1,008; 1,022 and 1,036 Da. For the linear homologs, the m/z values were about 1,012; 1,026; 1,040 and 1,056 Da. Having the objective to be applied in environmental and industrial fields, we proposed a functional characterization of the produced BioS, including the ST-reducing power, the determination of the critical micelle concentration (CMC), the oil dispersing activity (ODA) and the emulsification and foaming capacities. In order to increase the production yield, we followed the experimental design methodology. Additionally, we studied the effect of various physicochemical conditions on the BioS surface activity and stability.

The burned motor oil that served to determine the ODA was obtained from a local mechanic's station from Sfax, Tunisia.

The new BioS-producing strain Bacillus sp. MI27 was exploited in the present study. The inoculum was prepared in an LB liquid medium as described by (Mnif et al. 2021a, 2021b, 2021c). It was incubated overnight at 37 °C under agitation of 180 rpm. During the optimization study of BioS production, 4% (v/v) inoculums were passed into 250-mL shake flasks containing 50 mL of the respective sucrose-based medium (pH = 7.0). The medium composition was indicated in the optimization study part according to the experimental design. The pH was adjusted by 1 N NaOH. The prepared culture medium was incubated at 37 °C under shaking at 150 rpm for 24 h.

The experimental planning methodology was selected to optimize BioS production by Bacillus sp. MI27 on a sucrose-based medium under submerged fermentation. The optimization study was divided into two steps: screening of the most significant compounds by a Plackett and Burman design and their optimization by a central composite design (CCD).

In order to screen the most important medium compounds, a Plackett–Burman design was followed. This is a fractional plan that permits the exploration of up to ‘N-1’ variables with N experiments. It supposes the absence of interactions between the different media components. During the present study, 11 parameters were nominated to evaluate their effect on BioS production, including sucrose, yeast extract, ammonium sulfate, Na₂HPO₄, NaH₂PO₄, MgSO₄, NaCl, MnSO₄, FeSO₄, ZnSO₄ and CaCl₂. Table 1 presents the described media components and their corresponding higher and lower levels by a total of 12 experiments of the Hadamard matrix (run N°1–12). Two coded levels (−1 and +1) were attributed for each variable. The production of BioS was managed by ST, the ODA measurements and the quantification of the BioS yield (g/L).

In the second part of the optimization study, a CCD was adopted. They were conducted to predict an empirical model of the process, find out the optimum values of the most important factors and enhance BioS production. The Nemrod-W Version 2007 software (LPRAI, Marseille, France) was used to generate the design, including 16 experiments, namely 8 experiments of the full factorial design experiments (2³ = runs No. 1–8), 4 axial points (runs No. 9–12) and 4 replicates in the domain center (runs No. 13–16) to estimate the variability of the experimental results (Table 2). Three coded levels (−1, 0 and +1) were assessed for each variable. The response values (Y) denoted in each trial were the mean values of two repetitions. The BioS production was managed by the ST, the ODA and the BioS yield (g/L) measurements.

The multi-linear regression method served to estimate the model coefficients using the statistical software package (Nemrod-W by LPRAI Marseilles, France) as described in our previous works (Mnif et al. 2021b). The statistical significance of the model was evaluated on the basis of F-test with unequal variance (p < 0.05). The response surface graphs, which represent the system behavior, were plotted after the conduction of the regression analyses on the experimental data. The isoresponse contour plot qualified as a two-dimensional graphical representation that depicted the individual and cumulative effects of the parameters. Moreover, they are used to forecast the potential correlations that could occur between the different variables.

During the production experiments, a crude BioS extract was prepared according to the protocol described by Mnif et al. (2021a, 2021b). It consists of three consecutive cycles of acid precipitation–dissolution. The final BioS pellet was collected by centrifugation at 8,000 rpm/4 °C for 20 min, washed twice with acid distilled water (pH = 2) to eliminate any impurities and dissolved in alkaline-distilled water (pH = 8.0). After that, the concentration of the final dissolved extract was determined by the gravimetric method in order to quantify BioS production during the optimization study (Mnif et al. 2013a, 2013b). However, to characterize the produced BioS, the final extract was lyophilized and served as a crude lipopeptide preparation to evaluate the ST, the ODA, as well as the emulsification and foaming capacities.

The ST of the crude BioS was measured by a model Tensiometer Sigma 700, according to the Du-Noüy ring method. Except for special indications, experiments were realized at room temperature. To determine the CMC, we evaluated ST in the function of increasing BioS concentration. When an abrupt decrease in the ST was recorded, we denoted the CMC value (Mnif et al. 2021a, 2021b). It corresponds to the concentration at which BioS agglomerates into micelles.

The oil displacement test served to evaluate the ODA using burned motor oil. Assays were realized in a Petri dish with a diameter of 15 cm with 40 mL of distilled water. 100 μL of burned motor oil was dropped onto the surface of the water followed by the addition of 50 μL of the crude BioS. Hence, a clear zone of dispersion appeared and its diameter that corresponds to the ODA is recorded (Mnif et al. 2021a, 2021b).

The production of BioS by strain MI27 was evaluated by measuring the ST and the ODA in the supernatant and by the determination of the quantity produced by the gravimetric method. The experimental values of the three studied responses are presented in Table 1. The obtained results correspond to the average of three independent tests with two replicates for each test. For the percentage of reduction of ST, the results are between 45 and 58.16%; for the diameters of dispersion, they are between 1 and 9 cm; for the quantities produced, the results are between 0.064 and 1.04 g/L. All these results show a wide variability of the responses with a good correlation between them for each experiment studied, suggesting the right choice of the different parameters.

The operating conditions of the 18 experiments of the three-variable composite plane are described by the lines of the experimental plan (in real variables) represented in Table 2. For each experiment, we determined the ST reduction, the diameter of the ODA and the amount of BioS produced. The presented values correspond to the means of three separate experiments with two replicates for each experiment. The estimated values of the coefficients and their standard deviations are given in Table 3. As the values of the multiple linear correlation factors R² are equal to 0.953 for the ST decrease, 0.973 for the ODA and 0.975 for the BioS yield, we conclude that the overall quality of the regression is considered very good. The values of the correlation coefficient, which are very close to 1, show that there is a good correlation between the experimental and theoretical results for the different responses recorded.

with Y₁, Y₂ and Y₃ refer, respectively, to the three recorded responses, the decrease of the ST, the dispersion and the quantity produced. Combinations of factors (such as X₁*X₂) represent an interaction between individual factors. Factors X₁², X₂² and X₃² represent the double effect of the different factors X₁, X₂ and X₃. The values of the coefficients are calculated by the multiple linear regression method.

In order to confirm these optimal conditions, we have fixed the quantity of yeast extract at its optimal value, which is equal to 0.5%. Thus, an improved production yield of the order of 1.47 g/L with a dispersion diameter of the order of 10.10 cm and a ST decrease of the order of 60.68% can be achieved by working with 0.27% Na₂HPO₄ and 0.02% CaCl₂. Similar results were reached by setting the amount of Na₂HPO₄ at its optimum concentration of 0.27%. The corresponding isoresponse curves and surface plots are not presented. In order to see the variation of the second response studied, the dispersion diameter according to the factors studied, we fixed the amount of CaCl₂ to its maximal value, which is equal to 0.02% (Figure 2(b)). Analysis of the isoresponse curves representing the variation of the dispersion diameter as a function of the concentration of yeast extract and Na₂HPO₄ shows that it is possible to attain a diameter of the order of 10 cm with a 1.4 g/L BioS and a 60% ST reduction by working with 0.5% yeast extract and 0.27% Na₂HPO₂.

Additionally, in the study of the variation of the third response studied, the quantity produced by fixing the amount of CaCl₂ to its optimal value (0.02%) will allow obtaining the same optimal conditions found previously (Figure 2(c)). All the representations in Figures 2(a)–(c) confirm that the best production of BioS estimated at 1.41 g/L with a considerable ST decrease of the order of 60% (corresponding to a ST value of the order of 23.2 mN/m) and an ODA of about 10 cm can be obtained using 5 g/L yeast extract, 0.2 g/L CaCl₂ and 2.7 g/L Na₂HPO₄.

Generated optimum conditions were approved in four separate experiments, the mean of which corresponds to 1.4 g/L BioS, an average ST of 23 mN/m and an ODA of around 10 cm. Emulsifying (EI-24%) and foaming activities have been confirmed, suggesting a high production yield of BioS. Thus, the application of the experimental design methodology by a first screening plan of the most influential factors followed by a second CCD optimization plan allowed us to significantly improve the BioS production by the MI27 strain on sucrose-based medium. The composition of the culture medium is as follows: 2% sucrose, 0.27% Na₂HPO₄, 0.2% ammonium sulfate, 0.02% NaCl, 0.02% CaCl₂, 0.02% MgSO₄, 0.001% MnSO₄, 0.06% NaH₂PO₄, 0.005% FeSO₄ and 0.005% ZnSO₄.

In fact, the substitution of glucose by sucrose for the production of BioS allows a great economic gain. Also, adjusting the quantities of the various other components, including the nitrogen source and the mineral elements permits a significant decrease in the production cost with better quantities produced. The different nutritional parameters and their assigned levels strongly affect the BioS production yield and cost. Meanwhile, the applications of the experimental design methodology and response surfaces are experiencing a particular boom as fairly developed statistical tools to improve BioS production as they permit to adjust the media components (Bertrand et al. 2018). They also allow great economic gain and save time. Numerous factors can affect BioS production, namely the nutritional parameters as well as the physicochemical parameters including pH, temperature, agitation and aeration (Bertrand et al. 2018). Previous studies have delayed the application of Plackett and Burman designs along with the response surface methodology to select the most influential factors on lipopeptide BioS production, especially surfactin isoforms (Haddad et al. 2014; Liu et al. 2014; Meena et al. 2020).

As largely recognized, each BioS was characterized by the ST and CMC values that evaluate its efficiency (Mnif & Ghribi 2015a). We denote an improvement in the surfactant's effectiveness as the values of ST and CMC decrease. By way of comparison, we note, for example, that the MI27-derived BioS is more effective than surfactin isoforms produced by Bacillus subtilis isolate LSFM-05 (de Faria et al. 2011), those produced by B. subtilis SL having a CMC value of 154 mg/L and a ST of 28.68 mN/m (Wu et al. 2022) and surfactin isoforms produced by Bacillus nealsonii S2MT (Phulpoto et al. 2020). In means of the ST reduction power, it is more efficient than surfactin isoforms produced by B. subtilis BS-37 displaying a CMC value of mg/L (Liu et al. 2014), Bacillus amyloliquefaciens MO13-derived surfactin isoforms displaying a CMC value of 36 mg/L and an ST of 27 mN/m (Moro et al. 2022), engineered surfactin isoforms produced by B. subtilis 168 having a CMC value of 38–36 mg/L with potential ST of 28 mN/m (Hu et al. 2021) and surfactin isoforms derived from B. subtilis #309 having a CMC value of 15 mg/L with potential ST of 28 mN/m (Janek et al. 2021).

BioS are generally characterized by low CMCs with a better decrease in ST compared to chemical surfactants (Mnif et al.2021a, 2021b). In this aim, similar results were approved for MI27-derived BioS. As mentioned in our previous work, we determined the CMC and the ST decrease (γCMC) values of four chemical surfactants. The values are about 200 mg/L and 32 mN/m for the Triton X-100, 31 mg/L and 35 mN/m for the CTAB and 794 mg/L and 35 mN/m for SDS (Mnif et al. 2021b). On the basis of these values, the concluded results proved the effectiveness of Bacillus sp. MI27-derived BioS toward the three surfactants in terms of the ST decrease. For the CMC value, MI27-derived BioS is less efficient than the CTAB. However, all the results were found to favor the efficacy of the BioS of MI27 and its high application potential. Similar results suggesting the successful use of B. subtilis SPB1 in comparison to chemical surfactants in the bioremediation of dyes and hydrocarbons contaminated soil and water were denoted by Mnif et al. (2015a, 2015b, 2015c, 2016, 2017a).

In addition to the ST's decreasing power, BioS are able to disperse the oil. As shown in Figure 3(b), a maximum dispersion of around 120 mm is obtained at concentrations greater than or equal to 1,000 mg/L. There is a gradual increase in the dispersal area with the increase in BioS concentration, which will stabilize at a certain level. Thus, our BioS showed a good ability to disperse burned motor oil. Recent studies reported the ODA of bacterial-derived surfactin isoforms, suggesting their utility in the environmental field for the treatment of oil contaminants (Liu et al. 2014; Phulpoto et al. 2020; Barale et al. 2022).

A comparison of the ODA with that of chemical surfactants shows that the BioS of MI27 is significantly more effective. Indeed, maximum dispersion diameters of the order of 8.8, 9.2, 8.8 and 8.7 cm were obtained, respectively, with 900 mg/L Dehydol, 1,000 mg/L Triton X100, 1,000 mg/L CTAB and 85 mg/L SDS (Mnif et al. 2021c). Some literature studies show the effectiveness of hydrocarbon dispersal from BioS by contribution to chemical surfactants such as SDS, Tween 80 and Trition X100 (Das & Chandran 2011; Silva et al. 2014). Thus, having better efficiency and considering the toxicity of chemical surfactants, the BioS of MI27 presents a healthier and ecological alternative for various environmental applications. Basically, the enormous usage of petroleum-derived products imparts highly to water pollution provoking a major environmental risk to human health. The high hydrophobicity and solubility of hydrocarbons and vegetables inhibits their uptake and biodegradation by microorganisms. The bio-dispersion of these oils and hydrocarbons discharged to the surface of the water facilitates their disposal by physical methods. The use of BioS as a bio-dispersant is a better alternative due to its lower toxicity and biodegradability.

As shown in Figure 3(c), the BioS of MI27 shows a maximum emulsification of around 45%, which is obtained at concentrations greater than or equal to 1,000 mg/L. In this aim, numerous bacterial-derived surfactin, exhibited emulsification activities of around 67.6% for those derived from B. subtilis isolate LSFM-05 (de Faria et al. 2011), around 98% as reported by Long et al. (2017), around 55% for surfactin-like BioS produced by novel strain B. nealsonii S2MT (Phulpoto et al. 2020), between 58 and 64% for B. subtilis #309 derived surfactin (Janek et al. 2021) and between 56, 67, 54 and 60% for B. subtilis LS-derived surfactin isoforms (Wu et al. 2022). This emulsification property makes BioS excellent candidates for the bioremediation of water and soil contaminated with oils and hydrocarbons (Maier & Soberon 2000).

Owing to excellent surface activities, the lipopeptide derived from Bacillus sp. MI27 has potential use in the environmental field for the bioremediation of hydrocarbon-contaminated soil and water. Then, in order to enlarge its scope of application, we study its activity and stability at diverse and extreme physicochemical conditions. The abilities to decrease the ST, to disperse oil, to emulsify oil and to form foam were assessed at different pH values ranging from 2 to 10 and salt concentrations ranging from 0 to 5%. For the temperature, we evaluated only the ST reduction and oil dispersion from 10 to 80 °C. The ST was assayed at the CMC value of 120 mg/L and the other activities at 1,000 mg/L.

When observing the impact of elevated temperature on MI27 BioS stability, we remark a perfect thermal-stability, especially for the power of ST reduction (Figure 5(b)). The lipopeptide maintains about 100% of its ST reduction capacity and more than 90% of its ODA in the mentioned temperature values. These results are of growing interest as the prospective application of BioS in numerous industrial processes necessitates thermal stabilities. Previous research works exhibited similar findings (Chen et al. 2017; Ghazala et al. 2017; Kiran et al. 2017; Martins et al. 2018; Feng et al. 2019; Purwasena et al. 2019; Zouari et al. 2019; Jimenez et al. 2021; Mnif et al. 2021a, 2021b; Umar et al. 2021; Wu et al. 2022).

Figure 7(a) shows that the addition of sodium chloride significantly increases the ST reduction of the MI27 BioS at NaCl concentrations of 1.5 and 2% with a maximum activation of 110% in the presence of 1.5% NaCl. So we can suppose the activation of MI27-derived lipopeptide BioS by the Na⁺ cation. Additionally, it declared an emulsifying activity of interest for the different concentrations ranging from 0.5 to 5% with slight improvements. This activating effect of sodium chloride is similar to that of Huszcza & Burczyk (2003). A probable explanation for that is the modification of the molecular area of BioS by the effect to salt exposure (Thimon et al. 1992).

However, salinity inhibits the ODA of MI27-derived lipopeptide by losing more than 50% of its activity in the presence of concentrations greater than or equal to 1%. Additionally, we note a decrease of 14–58% of the MI27 emulsification power at NaCl concentrations ranging from 0.5 to 5%, respectively (Figure 7(Aa)). Nevertheless, MI27 lipopeptide has an interesting foaming power in the range of NaCl concentration studied (loses a maximum of 24% of its foaming activity to 5% NaCl) (Figure 7(Ab)). Numerous research works presented similar results (Mnif et al. 2013b, 2021a, 2021b; Pathak & Keharia 2014; Feng et al. 2019; Phulpoto et al. 2020). This good activity under saline conditions will allow the potential investigation of MI27 lipopeptide in the bioremediation of hydrocarbons contaminated seawater (Mnif et al. 2017a).

In addition to the study of MI27 BioS activity at different salt amounts, we explored its stability after pre-incubation in the presence of salts to mitigate seawater. Looking at Figure 7(Ba), we observe a perfect stability of the MI27 lipopeptide after measurement of the power of decrease of the ST (relative activities are around 100%) with activation of the ODA. As observed in Figure 7(Bb), for foaming power, there is a slight attenuation of activities at high NaCl concentrations of 3, 4 and 5%. Similar results are observed for emulsifying activity with higher attenuation than foaming power. These results go in favor of broadening its purview of use in different areas, especially for the enhanced oil recovery and biological remediation of sea water contamination(Chen et al. 2017; Ghazala et al. 2017; Kiran et al. 2017; Martins et al. 2018; Feng et al. 2019; Purwasena et al. 2019; Zouari et al. 2019; Jimenez et al. 2021; Mnif et al. 2021a, 2021b; Umar et al. 2021; Wu et al. 2022).

To conclude, experimental planning methodology was applied to maximize Bacillus sp. MI27 BioS production. The produced BioS illustrated interesting functional properties, especially its surface activity with potent emulsion-forming and foaming capacities. The crude lipopeptide preparation was characterized by great ST reduction, low CMC value along with emulsification, oil dispersing and foaming activities. The physicochemical characterization of the crude surfactin isoforms showed perfect activity and stability at extreme conditions of temperature, salinity and pH by means of the evaluation of their different functional properties. All these findings exhibited the prospective usage of MI27 lipopeptide preparation in industrial and environmental biotechnology.

All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted.

Informed consent was obtained from all individual participants included in the study.

All the authors gave the publisher the permission to publish the work in Water Practice and Technology.

The first author of this paper M.E. and the second author M.B. elaborated the experimental parts of the present work. The fourth author D.G. and the fifth author I.M. participated in the elaboration of the experimental plan of the work and corrected this paper.

The work is funded by the Ministry of Higher Education and Scientific Research.

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

The authors declare there is no conflict.