Biodegradation of RDX and HMX by a methanogenic enrichment culture

The biotransformation of RDX and HMX by a methanogenic enrichment culture was studied. The enrichment culture only degraded RDX when ethanol was included as an electron donor. Methane production, however, was only observed after RDX had been depleted. The addition of BESA inhibited methane production, but not ethanol fermentation nor RDX degradation. The addition of H-2 gas supported RDX degradation. HMX was also degraded, but the degradation rate (0.12 mu M day(-1)) was nearly 10-fold less than observed for RDX (1.6 mu M day(-1)). HMX degradation slowed when ethanol was depleted, but resumed after reamending the bottles with ethanol. The total number of anaerobes in the enrichment culture ranged from 1.5 x 10(5) to 1.6 x 10(6) ml(-1). Ethanol-fermenting syntrophs ranged from 1.5 x 10(4) to 1.6 x 105 ml(-1); H-2-utilizing methanogens ranged from 7.0 x 10(1) to 7.6 x 10(2) ml(-1); acetoclastic methanogens were <1.0 x 10(1) ml(-1); and H-2-utilizing acetogens ranged from 3.8 x 10(3) to 4.2 x 10(4) ml(-1). These findings indicate ethanol may serve as a source of H-2 for the RDX and HMX degrading bacteria. The presence of acetogens and a lack of CH4, production during ethanol degradation may indicate their involvement in the biodegradation of nitramine explosives.