Sunday, August 12, 2012
Columbia Hall, Terrace Level (Washington Hilton)
Aerobic bioremediation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) through the denitration pathway produces the end-product 4-nitro-2,4-diazabutanal (NDAB). Previous research has revealed a few microbes capable of NDAB degradation, however the mechanism remains unknown. Our hypotheses were that bacterial species capable of NDAB degradation exist naturally in environments contaminated with RDX, and that known explosive-degrading species may also be able to degrade NDAB. We enriched for bacteria that degraded NDAB from RDX-exposed environments. Soil and groundwater microcosms from Umatilla Chemical Depot demonstrated 35% NDAB degradation from 12 mg L-1 in 7 days in soil, but no degradation in groundwater. Wastewater sludge microcosms from Holston Army Ammunition Plant demonstrated 100% NDAB degradation in 48 hours. Since Methylobacterium sp. JS178 is a known NDAB-degrading strain, several Methylobacterium species were investigated for their ability to transform NDAB. Methylobacterium radiotolerans exhibited good growth and minimal biotransformation (20%) of NDAB over 7 days, while M. extorquens and M. thiocyanatum showed poor growth on NDAB with no biotransformation. Additionally, the role of NDAB as a carbon source for growth of strain JS178 was investigated and shown to be an unsuitable substrate and was not degraded. The potential of explosive-degrading isolates to transform NDAB was also examined. Bacillus and Pseudomonas species showed moderate growth with NDAB as the sole nitrogen source; no growth occurred for E. coli or Shewanella species. No biotransformation of NDAB was observed. Future goals include characterizing NDAB-degrading isolates from the microcosms and identifying the genes involved.