CHLOROFORM DECHLORINATION BY A WASTE-WATER METHANOGENIC CONSORTIUM AND CELL-EXTRACTS OF METHANOSARCINA-BARKERI

Whole-cell and cell-extract assays of a wastewater methanogenic consor tium 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 electr on donors like methanol, acetate, butyrate, but dechlorination rates i n the presence of glucose were 5-fold less. Methanogenesis in wastewat er samples was almost completely inhibited (reversibly) by as little a s 71 nM (8.5 ppb) aqueous CF, but DCM was only slightly inhibitory at 107 mu M (9.1 ppm) levels. The eubacterial antibiotics, ampicillin and streptomycin, inhibited approximately 40% of the dechlorination activ ity in the wastewater sample and the methanogenesis inhibitor bromoeth anesulfonic acid (BES) inhibited 90% of the dechlorination. CF dechlor ination 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 extrac ts of M. barkeri and 34% of the activity in the wastewater culture ext racts. Coenzyme M significantly reversed the BES inhibition of both me thanogenesis and CF dechlorination by whole cells of the wastewater cu lture, bur had no effect on cell-free extract dechlorination. Boiled c ell-free extracts had dechlorination rates that were 15 and 22% higher compared to unboiled rates in extracts from the wastewater culture an d M. barkeri, respectively. On the basis of these studies, it is propo sed that CF dechlorination in this wastewater sample is mediated by th e same catalysts found in M, barkeri and that these heat-stable cataly sts are functional in both the free and protein-bound forms. (C) 1997 Elsevier Science Ltd.