Potential role of Bacillus endospores in soil amended by olive mill wastewater

The main aim of this work was to know how spread is laccase activity in spores of Bacillus species isolated from a soil where Italian law allows olive mill wastewater (OMW) spreading, and to investigate the potential role of such autochthonous soil microorganisms in degradation of OMW phenols, and prevention of groundwater pollution. Laccase activity was detected for the first time in spores of wild-type Bacilluspumilus, B. cereus sensu lato, and B. amyloliquefaciens strains. Because B. pumilus, B. cereus sensu lato, and B. amyloliquefaciens, together with B. subtilis account for a total of 93% of Bacillus isolates at the study site, the nearly totality of Bacillus spores reveals laccase activity. Thus, taking also into consideration that Bacillus spores are more abundant (about 100-fold) than white-rot fungi (that possess a well known extracellular, radical-based ligninolytic enzyme system capable of degrading OMW phenols) in the studied soil, these spores may contribute to in-situ degradation of OMW phenols. This role is further emphasized by dilution of crude OMW during infiltration of rainwater through soil that allows to minimize the antibacterial activity of phenols. The widespread presence of Bacillus spores in soils indicates a potential detoxifying role of these spores in a broader context.