A SULFATE-REDUCING BACTERIUM FROM THE OXIC LAYER OF A MICROBIAL MAT FROM SOLAR LAKE (SINAI), DESULFOVIBRIO-OXYCLINAE SP-NOV

In an investigation on the oxygen tolerance of sulfate-reducing bacter ia, a strain was isolated from a 10(7)-fold dilution of the upper 3-mm layer of a hypersaline cyanobacterial mat (transferred from Solar Lak e, Sinai). The isolate, designated P1B, appeared to be well-adapted to the varying concentrations of oxygen and sulfide that occur in this e nvironment. In the presence of oxygen strain P1B respired aerobically with the highest rates [260 nmol O-2 min(-1) (mg protein)(-1)] found s o far among marine sulfate-reducing bacteria. Besides H-2 and lactate, even sulfide or sulfite could be oxidized with oxygen. The sulfur com pounds were completely oxidized to sulfate. Under anoxic conditions, i t grew with sulfate, sulfite, or thiosulfate as the electron acceptor using H-2, lactate, pyruvate, ethanol, propanol, or butanol as the ele ctron donor. Furthermore, in the absence of electron donors the isolat e grew by disproportionation of sulfite or thiosulfate to sulfate and sulfide. The highest respiration rates with oxygen were obtained with H-2 at low oxygen concentrations. Aerobic growth of homogeneous suspen sions was not obtained. Additions of 1% oxygen to the gas phase of a c ontinuous culture resulted in the formation of cell clumps wherein the cells remained viable for at least 200 h. It is concluded that strain P1B is oxygen-tolerant but does not carry out sulfate reduction in th e presence of oxygen under the conditions tested. Analysis of the 16S rDNA sequence indicated that strain P1B belongs to the genus Desulfovi brio, with Desulfovibrio halophilus as its closest relative. Based on physiological properties strain P1B could not be assigned to this spec ies. Therefore, a new species, Desulfovibrio oxyclinae, is proposed.