Dechlorination of p,p'-DDTs coupled with sulfate reduction by novel sulfate-reducing bacterium Clostridium sp. BXM.

A novel non-dsrAB (without dissimilatory sulfite reductase genes) sulfate-reducing bacterium (SRB) Clostridium sp. BXM was isolated from a paddy soil. Incubation experiments were then performed to investigate the formation of reduced sulfur compounds (RSC) by Clostridium sp. BXM, and RSC-induced dechlorination of p,p'-DDT in culture medium and soil solution. The RSCs produced were 5.8 mM and 4.5 mM in 28 mM sulfate amended medium and soil solution respectively after 28-day cultivation. The p,p'-DDT dechlorination ratios were 74% and 45.8% for 5.8mM and 4.5 mM RSCs respectively at 6h. The metabolites of p,p'-DDT found in the two reaction systems were identified as p,p'-DDD and p,p'-DDE. The dechlorination pathways of p,p'-DDT to p,p'-DDD and p,p'-DDE were proposed, based on mass balance and dechlorination time-courses. The results indicated that RSC-induced natural dechlorination may play an important role in the fate of organochlorines.