An NADH-rubredoxin oxidoreductase previously isolated from Desulfovibrio gigas [LeGall, J. (1 968) Ann. Inst. Pasteur 114, 109-1151 has now been fully purified and further characterized. It contains two subunits of 27 kDa and 32 kDa. With two mid-point redox potentials of -295 mV and -325 mV, this FMN-and FAD-containing protein can induce the specific reduction of D. gigas rubredoxin. In contrast, rubredoxins from the other Desulfovibrio species or desulforedoxin from D. gigas show very low reaction rates with the same enzyme. The phylogenetic significance of the narrow specificity of the enzyme toward the rubredoxin from the same organism is discussed. The purified enzyme has NADH oxidase activity with H,O, as a final product of 0, reduction. The reaction is half-inhibited by 4.2 pM p-cliloromercuribenzoate, whereas cyanide and azide are not significant inhibitors in this reaction. The role of this protein as a part of the enzymic equipment that allows the formation of ATP in the presence of oxygen from the degradation of carbon reserves is discussed.The small electron-carrying proteins, rubredoxins (6000 Da), have been found in the cytoplasm of several socalled strictly anaerobic sulfate-reducing bacteria, such asdesulfuricuns (27774) [3] and Therrnodesulfobacteriurn cornrnune [4]. The structures of rubredoxins from a variety of bacteria have been well studied and determined to atomic resolution [5][6][7]. The redox center of rubredoxin consists of a single iron atom (redox potential, -5 to 0 mV) [S], coordinated to four cysteinyl sulfur atoms. This redox potential is relatively high while dissimilatory sulfate reduction by Desulfovibrio species requires electrons from -400 to -200 mV [9-111. Hence, the search for the electron transfer reaction catalyzed by rubredoxin in Desulfovibrio species has remained elusive. Rubredoxins from other anaerobic bacteria were shown to function as an electron acceptor for a CO dehydrogenase reaction of Clostridiurn therrnoaceticurn and Acetobacterium woodii [ 121. A rubredoxin in Clostridiurn perj%ngens is involved in the reduction of nitrate to ammonia with NAD(P)H, concomitantly prompting the oxidation of organic substrates [13, 141. It has recently been shown that some sulfate-reducing bacteria are capable of some kind of aerobic respiration with the synthesis of ATP; also, the uncoupler carbonylcyanide rn-chlorophenylhydrazone stimulates the respiration rate and abolishes ATP formation [ 151. These bacteria have been reported to survive in the presence of oxygen at low respiration rates, conditions in which the reduction of sulfur compounds to sulfide is suppressed [15- 171. So far, no true oxygen oxidoreductase has been described from sulfate-reducing bacteria, and the detailed enzymological mechanisms of the utilization of 0, by 'strict anaerobes' have never been explored. However, since authentic superoxide dismutase and catalase have been characterized in Desulfovibrio [18], these bacteria are capable of the complete reduction of 0, to water whether the final product...

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A novel, moderately halophilic bacterium was isolated from the brine-seawater interface of the Shaban Deep, northern Red Sea. A polyphasic approach was used for the taxonomic characterization of this isolate, with the phenotypic and phylogenetic data clearly showing the distinctiveness of this bacterium. Cells of isolate E1L3A were Gram-negative, monotrichous cocci that showed a remarkable physiological flexibility, as could be seen by the quite broad growth ranges for oxygen, temperature, NaCl, and, to a smaller degree, pH. In addition, it was able to grow from atmospheric pressure up to 15 MPa, making it a piezotolerant bacterium. Phylogenetically, strain E1L3A represents a new, deeply branching lineage within the gamma-Proteobacteria, as determined by 16S rRNA gene sequence analysis. No close relatives are known so far, with sequence similarity to other cultivated members of the gamma-Proteobacteria being lower than 88%. The creation of the new genus Salinisphaera and the new species Salinisphaera shabanensis (DSM 14853; JCM 11575) for this new and highly versatile microorganism is therefore proposed.

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