Bacterial degradation of mixed-PAHs and expression of PAH-catabolic genes

Polyaromatic hydrocarbons (PAHs) are hazardous organic compounds with established toxicity, carcinogenicity, and mutagenicity, ubiquitous distribution, and persistence in different environmental matrices. In the present study, degradation of the mixture of PAHs (phenanthrene, anthracene, fluorene, and pyrene) by Kocuria flava and Rhodococcus pyridinivorans was investigated. The individual strains and consortium of both degraded 55.6%, 59.5%, and 59.1% of 10 mg L^-1 of mixed PAHs, respectively, within 15 days. The participation of catabolic enzymes [catechol 2,3-dioxygenase (C23O), dehydrogenase (DH), and peroxidase (POD)] was confirmed during catalytic oxidation through meta-cleavage of mixed PAHs in this study. The catabolic gene expression of naphthalene dioxygenase (NAH) and catechol 2,3-dioxygenase (C23O) during degradation was confirmed using RT-qPCR in the present study. This is the first study that shows significant gene expression of the catabolic genes during degradation of mixed PAHs by selected bacterial strains. The C23O gene showed a 6.02 log fold higher expression in Kocuria flava in comparison to Rhodococcus pyridinivorans whereas NAH gene exhibited a 7.9 log fold higher expression in Rhodococcus pyridinivorans in comparison to Kocuria flava. Hence it is likely to conclude that combination of Kocuria flava and Rhodococcus pyridinivorans can effectively remove hazardous mixture of PAHs from the contaminated environmental matrix.