Biodegradation kinetics and mechanism of 2,4,6-tribromophenol by Bacillus sp. GZT: a phenomenon of xenobiotic methylation during debromination.

A strain Bacillus sp. GZT capable of debrominating and mineralizing 2,4,6-tribromophenol (TBP) was isolated and characterized by morphological observation, biochemical and physiological identification as well as 16S rRNA sequence analysis. Biodegradation kinetics experiments demonstrated that initial TBP concentration had a predominant effect on degradation efficiency. Within 120h, the highest TBP degradation and debromination efficiencies were up to 93.2% and 89.3%, respectively, under the optimum condition. Ten metabolic intermediates including five brominated compounds, three oxidative products and two cellular metabolites were all identified by gas chromatography-mass spectrometer, and six key intermediates were doubly validated by authentic standards. The proposed biodegradation mechanism inferred that reductive debromination as a major degradation pathway could simultaneously take place at ortho- and para-positions on TBP, while methylated debromination was also found as a minor degradation pathway during this process. Within 148h degradation, nearly one-third of 3mg/L TBP could be completely mineralized.