Electrogenic degradation of Reactive Red 152 dye by Niallia circulans DC10 and its genome sequence analysis reveals genes mediating dye degradation and anodic electron transfer

This study demonstrates the application of a newly isolated bacterium N. circulans DC10 for the degradation of azo dye Reactive Red 152 (RR152) and bio-electricity generation in a microbial fuel cell (MFC) system. When used as an anodic biocatalyst, N. circulans DC10 achieved 94.78 ± 1.17% decolourization and 89.55 ± 2.28% COD reduction within 72 h in the MFC system along with 166.48 mW/m2 maximum power density generation. The FT-IR and GC–MS analysis suggested that N. circulans DC10 utilizes the phenylacetic acid catabolic pathway for degradation of RR152 in the dual chamber MFC system. The genome sequence analysis of N. circulans DC10 revealed the presence of flavin mononucleotide (FMN) dependant-NADH azoreductase gene azoR and a cluster of genes, most of which participate in the biosynthesis of type IV pili (T4P), an extracellular appendage. The RT-qPCR analysis showed that the expression levels of azoR gene increased around seven folds and T4P assembly genes pilT/pilZ expression levels increased more than two folds in N. circulans DC10 during active biodegradation of RR152 in the anode of MFC systems as compared to the static control flask cultures. The obtained results suggest that T4P has a role in promoting cell adherence to the surface of anode by N. circulans DC10 for exo-electron transfer generating bioelectricity. The cumulative effect of azoR and type IV pilus assembly genes resulted in efficient bio-electrogenic degradation of azo dye RR152 in the MFC system.