Desulfitobacterium hafniense sp. nov., an anaerobic, reductively dechlorinating bacterium

Strain DCB-2(T) (T = type strain) (T. Madsen and D. Licht, Appl. Environ. Microbiol. 58:2874-2878, 1992) is an anaerobic, spore-forming bacterium that is capable of reductive dechlorination of chlorophenols. The cells of this strain are rod shaped and 3.3 to 6 μm long by 0.6 to 0.7 μm wide and occur singly and in pairs. Short chains are formed. Spores are terminal. This bacterium is motile, and each cell has one or two terminal flagella. Cells in the exponential and stationary phases are gram negative. This organism does not hydrolyze gelatin and is indole positive and catalase negative, and the guanine-plus-cytosine content of its cellular DNA is 47 mol%. The optimum temperature for growth is 37°C. Only pyruvate and tryptophan are used as substrates. Pyruvate and 2,4,6-trichlorophenol are converted to acetate, CO2, and 4-chlorophenol by strain DCB-2(T). When grown on pyruvate, this bacterium produces sulfide if thiosulfate or sulfite is added as an electron acceptor. Fe(III) is reduced to Fe(II), but Mn(IV) is not reduced. Sulfate is not reduced to sulfide in the presence of pyruvate or other carbon sources typically used by sulfate-reducing bacteria. Cytochrome c is present, but desulfoviridin is not. DCB-2(T) reductively dechlorinates 3-chloro-4- hydroxyphenylacetate to 4-hydroxyphenylacetate and conserves energy from the reaction. 16S rRNA sequencing revealed that strain DCB-2(T) clusters with the Clostridium-Bacillus subphylum and groups with Desulfitobacterium dehalogenans and Desulfotomaculum orientis. Desulfotomaculum orientis does not dechlorinate 2,4,6-trichlorophenol. On the basis of the phylogenetic and physiological differences and similarities of strain DCB-2(T), Desulfitobacterium dehalogenans, and Desulfotomaculum orientis, we concluded that DCB-2(T) belongs to the genus Desulfitobacterium. We propose that strain DCB-2 is the type strain of Desulfitobacterium hafniense sp. nov.