Since these bacteria are killed by exposure to atmospheric oxygen, the environmental niches most frequently occupied by these bacteria are anaerobic.

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1 Sulfate-reducing bacteria (SRB) are most notable for the conspicuous end product of their respiratory metabolism, hydrogen sulfide, which is chemically reactive and quite toxic to plants, animals and humans. Since these bacteria are killed by exposure to atmospheric oxygen, the environmental niches most frequently occupied by these bacteria are anaerobic. Thus members of the SRB are classified by only two characteristics, their oxygen sensitivity and their ability to use sulfate as a terminal electron acceptor. This sweeping classification includes many types of bacteria, Gram negative and positive, mesophilic and thermophilic, marine and freshwater, Eubacteria and Archaea. However, members of the genus Desulfovibrio are the most readily cultured and are the only SRB that have been subjected to molecular biological analysis.

2 Sulfate reduction is a dominant anaerobic carbon oxidation pathway along the margins accounting for the oxidation of 50% of the total organic carbon in some systems

3 More recent studies (Lovley et al., 1993) have documented the ability of a number of Desulfovibrio strains to reduce toxic metals such as uranium and chromium, a process that results in the production of less water-soluble species.

4 The distinguishing characteristics of Desulfovibrio species are that they contain desulfoviridin. Desulfovibrio oxidize their energy source to that of acetate and excrete this as their end product. Desulfovibrio also uses hydrogen, lactate, and pyruvate as electron donrs. This genus can grow easily on a sulfate-lactate medium in the absence of oxygen. There are a number of species fwithin the genus Desulfovibrio.

5 The economic and environmental processes which have historically driven the desire to understand the metabolism of the SRB include underground corrosion of iron or steel gas or water pipes and generation of noxious sulfide during digestion of domestic and agricultural wastes. These bacteria have been a particular problem for the petroleum industry not only because of their role in metal corrosion but also because of the souring of the petroleum by the hydrogen sulfide generated and the health hazard presented by this gas. In particular, the possibility that these bacteria utilize a novel hydrogen cycling mechanism to generate or augment the proton gradient across the cytoplasmic membrane (Odom and Peck, 1981) has stimulated much discussion.

6 Obligate anaerobes. Curved rod-shaped cells x um; Non-spore forming. Gram negative; Polarly flagellated. Contains desulfoviridin; It is a sulfate-reducing Proteobacteria. Desulfovibrio desulfuricans

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8 List of Species List of Species Desulfovibrio acrylicus Desulfovibrio aespoeensis Desulfovibrio aestuarii Desulfovibrio africanus Desulfovibrio alaskensis Desulfovibrio alcoholivorans Desulfovibrio aminophilus Desulfovibrio baarsii Desulfovibrio baculatus Desulfovibrio bastinii Desulfovibrio burkinensis Desulfovibrio capillatus Desulfovibrio carbinolicus Desulfovibrio cuneatus Desulfovibrio desulfuricans Desulfovibrio desulfuricans subsp. desulfuricans Desulfovibrio desulfuricans subsp. termitides Desulfovibrio ferrophilus Desulfovibrio fluorescens Desulfovibrio fructosivorans Desulfovibrio gabonensis Desulfovibrio giganteus Desulfovibrio giganteus subsp. termitides Desulfovibrio gigas Desulfovibrio gracilis Desulfovibrio halophilus Desulfovibrio hydrothermalis Desulfovibrio indonesiensis Desulfovibrio inopinatus Desulfovibrio intestinalis Desulfovibrio litoralis Desulfovibrio longus Desulfovibrio magneticus Desulfovibrio mexicanus Desulfovibrio orientis Desulfovibrio oxyclinae Desulfovibrio piger Desulfovibrio profundus Desulfovibrio salexigens Desulfovibrio sapovorans Desulfovibrio senezii Desulfovibrio simplex Desulfovibrio sp. Desulfovibrio sulfodismutans Desulfovibrio termitidis Desulfovibrio thermophilus Desulfovibrio vietnamensis Desulfovibrio vulgaris subsp. oxamicus Desulfovibrio vulgaris subsp. vulgaris Desulfovibrio zosterae

9 Members of the genus Desulfovibrio commonly reside in the soil and aquatic habitats. Since these organisms are strict anaerobes, both aquatic and terrestrial environments are made anoxic as a result of microbial decomposition. The surrounding elements in such an environment are rich in organic material and in sulfate. Isolation of Desulfovibrio is facilitated by using the anoxic lactate-sulfate medium with ferrous iron incorporated into the culture. As the sulfate is reduced to sulfite, the sulfite interact with the ferrous iron to generate a black medium (see Figure B to the left). This new medium is chemically called ferrous sulfide and it is insoluble. The blackening of the culture indicates that sulfate reduction is taking place and that the iron is acting as a detoxifier for the harmful sulfide; thus, enabling a higher growth yield for the sulfate-reducing bacteria to grow. To further isolate the sulfatereducing bacteria, streaking can be used both on a Petri plate or in roll tubes. The shaken tube method involves placing a small amount of liquid with the bacteria in the agar growth medium and diluted. Once the medium is solidified, black colonies of the bacteria will appear and can be cultivated into a pure culture. Due to how common Desulfovibrio is found in both aquatic and terrestrial habitats, this genus is the most studied of the sulfate-reducing proteobacteria.

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11 Desulfovibrio vulgaris is a model for the study of the energy metabolism of sulfate-reducing bacteria. Sulfate-reducing bacteria have an important economic impact because they are involved in biocorrosion of ferrous metals in anaerobic environment. For example, their metabolism has several negative consequences for the petroleum industry (e.g. corrosion of the pumping machinery). These bacteria also contribute to bioremediation of toxic metal ions.

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