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 5.8 mM and 4.5 mM RSCs respectively at 6 h. 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. Highlights: ► Non-dsrAB SRB Clostridium sp. BXM was isolated from a paddy soil. ► Clostridium sp. BXM could utilize thiosulfate and sulfate as electron acceptor. ► The SRB-produced RSC represented abiotic DDT-dechlorination. ► The dechlorination was RSC/sulfate amount dependent. - The RSC-induced dechlorination mediated by a novel non-dsrAB sulfate-reducing bacterium may play an important role in fate of organochlorines.