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Science of The Total Environment
2016

Identification of groundwater microorganisms capable of assimilating RDX-derived nitrogen during in-situ bioremediation

Kun-Ching Cho, Mark E. Fuller, Paul B. Hatzinger, Kung-Hui Chu

Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843-3136, USA.

Abstract

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a nitroamine explosive, is commonly detected in groundwater at military testing and training sites. The objective of this study was to characterize the microbial community capable of using nitrogen derived from the RDX or RDX intermediates during in situ bioremediation. Active groundwater microorganisms capable of utilizing nitro-, ring- or fully-labeled 15N-RDX as a nitrogen source were identified using stable isotope probing (SIP) in groundwater microcosms prepared from two wells in an aquifer previously amended with cheese whey to promote RDX biodegradation. A total of fifteen 16S rRNA gene sequences, clustered in Clostridia, β-Proteobacteria, and Spirochaetes, were derived from the 15N-labeled DNA fractions, suggesting the presence of metabolically active bacteria capable of using RDX and/or RDX intermediates as a nitrogen source. None of the derived sequences matched RDX-degrading cultures commonly studied in the laboratory, but some of these genera have previously been linked to RDX degradation in site groundwater via 13C-SIP. When additional cheese whey was added to the groundwater samples, 28 sequences grouped into BacteroidiaBacilli, and α-, β-, and γ-Proteobacteria were identified. The data suggest that numerous bacteria are capable of incorporating N from ring- and nitro-groups in RDX during anaerobic bioremediation, and that some genera may be involved in both C and N incorporation from RDX.

Graphical abstract

Keywords: RDX; SIP; Groundwater; Bioremediation; Biodegradation.
 
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