Chloroform dechlorination by a wastewater methanogenic consortium and cell extracts of Methanosarcina barkeri

Whole-cell and cell-extract assays of a wastewater methanogenic consortium and cell extracts of Methanosarcina barkeri strain MS were shown to dechlorinate chloroform (CF), predominantly to dichloromethane (DCM). The wastewater cell dechlorination reaction was supported by electron donors like methanol, acetate, butyrate, but dechlorination rates in the presence of glucose were 5-fold less. Methanogenesis in wastewater samples was almost completely inhibited (reversibly) by as little as 71 nM (8.5 ppb) aqueous CF, but DCM was only slightly inhibitory at 107 μM (9.1 ppm) levels. The eubacterial antibiotics, ampicillin and streptomycin, inhibited approximately 40% of the dechlorination activity in the wastewater sample and the methanogenesis inhibitor bromoethanesulfonic acid (BES) inhibited 90% of the dechlorination. CF dechlorination rates were similar in cell extracts of M. barkeri (222 nmol CF/min/mg protein) and a wastewater enrichment culture (177 nmol CF/min/mg protein). BES inhibited 41% of the CF dechlorination in cell extracts of M. barkeri and 34% of the activity in the wastewater culture extracts. Coenzyme M significantly reversed the BES inhibition of both methanogenesis and CF dechlorination by whole cells of the wastewater culture, but had no effect on cell-free extract dechlorination. Boiled cell-free extracts had dechlorination rates that were 15 and 22% higher compared to unboiled rates in extracts from the wastewater culture and M. barkeri, respectively. On the basis of these studies, it is proposed that CF dechlorination in this wastewater sample is mediated by the same catalysts found in M. barkeri and that these heat-stable catalysts are functional in both the free and protein-bound forms