Anovel Sphingobacterium sp. RB, a rhizosphere isolate degrading para-nitrophenol with substrate specificity towards nitrotoluenes and nitroanilines

Sphingobacterium sp. RB, a novel bacterial strain isolated from a soil sample, was able to utilize para-nitrophenol (PNP) as sole source of carbon and energy at high concentrations (1.0-5.0 mM). The culture completely degraded 3.0 mM PNP within 36 h with proportionate increase in biomass. With 5.0 mM PNP (700 ppm), 70% degradation was observed within 72 h of incubation. Scanning electron microscope images of the isolate in the presence and absence of PNP showed no significant morphological variations. Liquid chromatography-mass spectrometry analysis indicated that the biodegradation of PNP in this bacterium proceeded via the formation of 1,2,4-benzenetriol. Cells previously exposed to PNP (induced) were 30% more effective in degrading PNP. With catechol and phenol, such induction was not observed. Uninduced cells of Sphingobacterium sp. RB were capable of degrading a variety of other nitroaromatic compounds, including 2-nitroaniline, 2,4-dinitroaniline, 2-nitrotoluene, 3-nitrotoluene and 2,4-dinitrophenol, within 72 h, thus proving its candidacy as a potent bioremediation agent. To the best of our knowledge, this is the first report on a Sphingobacterium species degrading PNP via formation of 1,2,4-benzenetriol.