Application of 13C-stable isotope probing to identify RDX-degrading microorganisms in groundwater

We employed stable isotope probing (SIP) with 13C-labeled hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to identify active microorganisms responsible for RDX biodegradation in groundwater microcosms. Sixteen different 16S rRNA gene sequences were derived from microcosms receiving 13C-labeled RDX, suggesting the presence of microorganisms able to incorporate carbon from RDX or its breakdown products. The clones, residing in Bacteroidia, Clostridia, α-, β- and δ-Proteobacteria, and Spirochaetes, were different from previously described RDX degraders. A parallel set of microcosms was amended with cheese whey and RDX to evaluate the influence of this co-substrate on the RDX-degrading microbial community. Cheese whey stimulated RDX biotransformation, altered the types of RDX-degrading bacteria, and decreased microbial community diversity. Results of this study suggest that RDX-degrading microorganisms in groundwater are more phylogenetically diverse than what has been inferred from studies with RDX-degrading isolates. Highlights: •SIP identified sixteen groundwater bacteria capable of using RDX and/or its metabolites as a carbon source. •The RDX degraders in groundwater are phylogenetically diverse and different from known RDX degraders. •Cheese whey induced community shift and altered diversity of the RDX-degrading microorganisms over time. -- RDX-degrading bacteria in contaminated groundwater, identified by SIP with 13C-labeled RDX, are phylogenetically diverse and different from known RDX degraders