Physiology of Desulfomonile tiedjei, a strictly anaerobic bacterium capable of reductive dehalogenation

Desulfomonile tiedjei (formerly strain DCB-1) is a strictly anaerobic bacterium which is capable of reductive dehalogenation of benzoates and ethylenes. This reaction is of possible significance for bioremediation of toxic wastes and pollutants. The organism is not closely related to any other known bacterium. General physiological studies were undertaken for the following purposes: (1) to better classify D. tiedjei, (2) to understand what physiological significance reductive dehalogenation has for this organism, (3) to devise strategies for the isolation of other dehalogenating anaerobes and (4) to better understand ecological principles which might affect reductively dehalogenating organisms in natural environments. D. tiedjei was determined to be a sulfate-reducing bacterium capable of reducing sulfate and thiosulfate stoichiometrically to sulfide with the following electron donors: H{dollar}sb2{dollar}, formate, CO, lactate, pyruvate, butyrate and 3-methoxybenzoate. In the absence of an electron donor, thiosulfate was instead fermented to sulfide plus sulfate. D. tiedjei grew by a novel fermentation of pyruvate plus CO{dollar}sb2{dollar}, the latter serving as an electron acceptor and being reduced to acetate. Carbon monoxide dehydrogenase activity indicated that CO{dollar}sb2{dollar} reduction was probably via the acetyl coenzyme A pathway. Autotrophic and diazotrophic growth were possible. 3-chlorobenzoate, which was reductively dehalogenated to benzoate, also served as an electron acceptor for energy metabolism. This reaction was stoichiometrically coupled to oxidation of formate to CO{dollar}sb2{dollar}. D. tiedjei was grown on formate plus 3-chlorobenzoate in defined medium. Resuspended cells catalyzed dehalogenation-dependent ATP synthesis. The effects of respiratory inhibitors suggest that dehalogenation and ATP synthesis are coupled via a chemiosmotic mechanism. The effects of an ATPase inhibitor and of imposed pH gradients suggest that a proton-driven ATPase is involved in the above chemiosmotic process. Thus, reductive dehalogenation appears to be a novel mode of anaerobic respiration. Isolation of other dehalogenating anaerobes was attempted using strategies based on the above findings. One isolate very similar to D. tiedjei was obtained, but the dehalogenating agents in the majority of enrichment cultures used were not isolated.