Exposure to nitro-compounds like RDX, TNT contained in unexploded ordinance pose significant risks for people and the environment due to their toxicity and explosive nature. Bombing sites used for military training activities contain considerable amounts of these contaminants. Until 2003 and for more than 60 years, the US Navy used the eastern part of Vieques, Puerto Rico as a bombing range. Since then, leaching of explosive compounds like RDX from unexploded ordnance represents a serious threat to the marine ecosystem of the area. The contribution of sulfate-reducing bacteria (SRB) to natural attenuation of explosives has been demonstrated in freshwater environments; however, little is known about their contribution in marine environments. From the contaminated sediments, we isolated 5 novel SRBs using lactate as the sole electron donor. Preliminary 16S rDNA analyses identify all 5 isolates to be delta proteobacteria most closely related to Desulfovibrio, with 16S rDNA sequences less than 94percent of similarity with known sequences, thus representing putative new species. In general, the isolates grew best at 37oC, at a pH of 7.5 and optimal growth was obtained with 1.5-3percent of salt added in the media. While all isolates grew with pyruvate as the alternative electron donor, 3 of the isolates grew with 20mM glycerol, one of them showed growth on 50mM fumarate. Electron acceptors sulfate, sulfite and thiosulfate were reduced by all isolates. Preliminary results indicate two of the isolates could also reduce Mn(IV). Some of the bacterial isolates grew better in explosive-amended media. The growth and survival in the presence of TNT increased with added salinity of the media. Based on this result and the fact that the isolates have had prior exposure to explosives, investigations are underway to study the potential of RDX degradation by the novel isolates.
