Bacterial community structures and functional gene diversity of toluene denitrifying degraders in coking contaminated enrichments.

Contaminated soil and wastewater involving coking process contain large amounts of aromatics, and biotreatment of the soil and sludge requires adequate understanding of pathways involved in the metabolisms of aromatic degraders. It is known that the ring cleavage within benzoyl-CoA pathway is encoded by the hydrolase gene (bamA). This study analyzed denitrifying bacterial community structures and bamA gene diversity of mixed cultures enriched from soils or activated sludge due to coking process. The sole electron donor of the enrichments was toluene or benzoate, a key intermediate product during toluene degradation, and the electron acceptor was nitrate. The 16S rRNA gene analysis by Illumina sequencing presented diversified bacterial community structures among four active cultures, including main phyla of Proteobacteria and Firmicutes for the toluene cultures and Proteobacteria and Bacteroidetes for the benzoate cultures. In particular, Alphaproteobacteria were found to contribute much to the degradation of toluene, while Betaproteobacteria contributed much to the degradation of benzoate. It's interesting that the bamA gene diversity in our enrichments is different from the reported studies, suggesting the novel bamA variants in coking contaminated soil or sludge. And the potential application of bamA as a biomarker for the biodegradation processes anaerobically was also proved. Both 16S rRNA and bamA analyses found that Thauera was the main genus in the enrichments. The differences between the cultures enriched from both soil and sludge were explored as well, providing some evidence for application of activated sludge as the source of acclimated degraders on bioremediation of coking contaminated soil. [ABSTRACT FROM AUTHOR]