The ecology and biochemistry of reductive dehalogenation reactions: Studies in anaerobic bacterial consortia and the model microorganism Desulfomonile tiedjei.

摘要

The biodegradation of 3-chlorobenzoate (3CBz) by microorganisms in the presence of sulfate was investigated. After a lag period, 3CBz was degraded concurrent with sulfate reduction. Chlorine removal from dichlorobenzoates confirmed that reductive dehalogenation was the initial fate process. Sulfate did not influence 3CBz degradation rates in acclimated cultures but accelerated the development of 3CBz degradation activity in fresh transfers. Mass balance determinations revealed that methane was the dominant electron-accepting process. Molybdate inhibited sulfate reduction and 3CBz dehalogenation to a similar extent but did not effect benzoate biodegradation. We conclude that reductive dehalogenation and sulfate reduction occur concurrently in these enrichments and that the sulfate-dependent stimulation was likely due to the acceleration of benzoate oxidation.;Separate mechanisms of inhibition due to sulfate, sulfite, and thiosulfate under growth versus nongrowth conditions were observed in D. tiedjei. Cells grown in the presence of 3CBz, the substrate/inducer for the aryl dehalogenase, and either sulfate, sulfite, or thiosulfate contained reduced level of dehalogenation activity indicating that sulfur oxyanions repress the requisite enzymes. In membrane fractions lacking the cytoplasmically-located sulfur oxyanion reductases cells, thiosulfate and sulfite, but not sulfate, were potent inhibitors of aryl dehalogenation activity. These results suggest that under growth conditions, sulfur oxyanions serve as preferred electron acceptors and negatively influence dehalogenation activity in D. tiedjei by regulating the amount of aryl dehalogenase in cells, but in vitro inhibition is due to the interaction of reactive species with enzymes involved in dehalogenation.;The dehalogenation of tetrachloroethylene by Desulfomonile tiedjei was characterized and compared to this organism's 3C8z dehalogenation activity. Tetrachloroethylene was dehalogenated to tri- and di-chloroethylene. Tetrachloroethylene dehalogenation was heat sensitive, not oxygen labile, and increased in proportion to the amount of protein. Both dehalogenation activities were dependent on hydrogen or formate as electron donors, had an absolute requirement for either methyl viologen or triquat as electron carriers, and appear to be catalyzed by integral membrane proteins with similar solubilization characteristics. Dehalogenation of tetrachloroethylene was inhibited by 3-chlorobenzoate but not 2- or 4-chlorobenzoate. These findings suggest that the dehalogenation of tetrachloroethylene in D. tiedjei is catalyzed by a dehalogenase previously thought to be specific for meta-halobenzoates.