Desulfitobacterium spp. are strictly anaerobic bacteria that were first isolated from environments contaminated by halogenated organic compounds. They are very versatile microorganisms that can use a wide variety of electron acceptors, such as nitrate, sulfite, metals, humic acids, and man-made or naturally occurring halogenated organic compounds. Most of the Desulfitobacterium strains can dehalogenate halogenated organic compounds by mechanisms of reductive dehalogenation, although the substrate spectrum of halogenated organic compounds varies substantially from one strain to another, even with strains belonging to the same species. A number of reductive dehalogenases and their corresponding gene loci have been isolated from these strains. Some of these loci are flanked by transposition sequences, suggesting that they can be transmitted by horizontal transfer via a catabolic transposon. Desulfitobacterium spp. can use H2 as electron donor below the threshold concentration that would allow sulfate reduction and methanogenesis. Furthermore, there is some evidence that syntrophic relationships occur between Desulfitobacterium spp. and sulfate-reducing bacteria, from which the Desulfitobacterium cells acquire their electrons by interspecies hydrogen transfer, and it is believed that this relationship also occurs in a methanogenic consortium. Because of their versatility, desulfitobacteria can be excellent candidates for the development of anaerobic bioremediation processes. The release of the complete genome of Desulfitobacterium hafniense strain Y51 and information from the partial genome sequence of D. hafniense strain DCB-2 will certainly help in predicting how desulfitobacteria interact with their environments and other microorganisms, and the mechanisms of actions related to reductive dehalogenation.

An anaerobic bacterium, strain PCP-lT (T = type strain), which dechlorinates pentachlorophenol (PCP) to 3-chlorophenol, was isolated from a methanogenic consortium. This organism is a spore-forming rod-shaped bacterium that is nonmotile, asaccharolytic, and Gram stain negative but Gram type positive as determined by electron microscopic observations. Inorganic electron acceptors, such as sulfite, thiosulfate, and nitrate (but not sulfate), stimulate growth in the presence of pyruvate and yeast extract. The optimum pH and optimum temperature for growth are 7.5 and 38"C, respectively. The dechlorination pathway is: PCP -+ 2,3,4,5-tetrachlorophenol + 3,4,5-trichlorophenoI + 3,5-dichlorophenol + 3-chlorophenol. This bacterium dechlorinates several different chlorophenols at ortho, meta, and para positions; exceptions to this are 2,3-dichlorophenol, 2,5-dichlorophenol, 3,4-dichlorophenol, and the monochlorophenols. The time course of PCP dechlorination suggests that two enzyme systems are involved in dehalogenation in strain PCP-lT. One system is inducible for ortho dechlorination, and the second system is inducible for meta and para dechlorinations. A 16s rRNA analysis revealed that strain PCP-lT exhibits 95% homology with Desu@tobacterium dehalogenans JW/IU-DCl, an anaerobic bacterium which can dehalogenate chlorophenols only in ortho positions. These results suggest that strain PCP-lT is a member of a new species and belongs to the recently proposed genus DesuZjhbacteriurn. Strain PCP-lT differs from D. dehalogenans JW/IU-DCl by its broader range of chlorophenol dechlorination. Strain PCP-1 is the type strain of the new species, DesuEftobacterium frappieri.Only a few anaerobic bacteria that can reductively dechlorinate chlorophenols have been isolated in pure culture. Desulfornonile tiedjei DCB-1 is the best-described dechlorinating anaerobic bacterium to date (7). This organism is a strictly anaerobic, gram-negative, sulfate-reducing bacterium that obtains energy for growth from reductive dehalogenation of 3-chlorobenzoate with formate as an electron donor (8, 19). In the presence of 3-chlorobenzoate, this strain can also dechlorinate rneta-substituted halobenzoates (9, 15) and chlorophenols (18). Madsen and Licht (16) isolated a Clostridium-like microorganism, strain DCB-2, that can dechlorinate 2,4,6-chlorophenol to 2,4-chlorophenol and finally to 4-chlorophenol; removal of rneta-substituted chlorine has been observed only with 3,s-chlorophenol. DesulJitobacteriurn dehalogenans JWf IU-DC1, a gram-positive anaerobic bacterium, can dehalogenate a wide range of chlorophenols, including pentachloropheno1 (PCP) and related compounds, at the ortho position (22, 23). This strain can use various alternative electron acceptors, including sulfur, sulfoxy anions (except sulfate), nitrate, and fumarate. Recently, a novel, gram-negative, facultatively anaerobic, rod-shaped bacterium which can grow anaerobically via reductive dehalogenation of 2-chlorophenol was isolated (5). This microaerophilic bacterium is a member of th...

Enterobacter cloacae strain EM was isolated from a commercial dietary mineral supplement stabilized by a mixture of methylparaben and propylparaben. It harbored a high-molecular-weight plasmid and was resistant to high concentrations of parabens. Strain EM was able to grow in liquid media containing similar amounts of parabens as found in the mineral supplement (1,700 and 180 mg of methyl and propylparaben, respectively, per liter or 11.2 and 1.0 mM) and in very high concentrations of methylparaben (3,000 mg liter ؊1 , or 19.7 mM). This strain was able to hydrolyze approximately 500 mg of methyl-, ethyl-, or propylparaben liter ؊1 (3 mM) in less than 2 h in liquid culture, and the supernatant of a sonicated culture, after a 30-fold dilution, was able to hydrolyze 1,000 mg of methylparaben liter ؊1 (6.6 mM) in 15 min. The first step of paraben degradation was the hydrolysis of the ester bond to produce 4-hydroxybenzoic acid, followed by a decarboxylation step to produce phenol under aerobic conditions. The transformation of 4-hydroxybenzoic acid into phenol was stoichiometric. The conversion of approximately 500 mg of parabens liter ؊1 (3 mM) to phenol in liquid culture was completed within 5 h without significant hindrance to the growth of strain EM, while higher concentrations of parabens partially inhibited its growth.

An anaerobic bacterium that transforms phenol and 4-hydroxybenzoate (4-OHB) into benzoate, strain LR7.2T, was isolated from a culture originating from a mixture of swamp water, sewage sludge, swine waste and soil. Cells of strain LR7.2T are Gram-positive short rods (1×2 μm) that are electron-dense when observed by electron microscopy. The optimum pH and temperature for growth and transformation activity of 4-OHB are 7·5–8·0 and 30–37 °C, respectively. The bacterium does not use sulphate, thiosulphate, nitrate, nitrite, FeCl3, fumarate or arsenate as an electron acceptor. It does not normally use sulphite, although stimulation of growth and 4-OHB transformation activity at a low concentration (up to 2 mM) has been reported previously under different culture conditions. The presence of 4-OHB or phenol is essential for growth; transformation of 4-OHB or phenol into benzoate is used to produce energy for growth. Using [6D]-phenol, 4-OHB was shown to be an intermediate in the transformation of phenol into benzoate. No spore was observed. The bacterium has a DNA G+C content of 51 mol% and its major membrane fatty acid is anteiso-C15 : 0. The 16S rRNA gene sequence of strain LR7.2T shows only 90 % similarity to its closest relative (Pelotomaculum thermopropionicum). From these results, a new taxon is proposed: Cryptanaerobacter phenolicus gen. nov., sp. nov. The type strain is LR7.2T (=ATCC BAA-820T=DSM 15808T).