PSYCHROTOLERANT SULFATE-REDUCING BACTERIA FROM AN OXIC FRESH-WATER SEDIMENT, DESCRIPTION OF DESULFOVIBRIO-CUNEATUS SP. NOV. AND DESULFOVIBRIO-LITORALIS SP. NOV

The most abundant culturable sulfate-reducing bacteria were isolated f rom the littoral sediment of the oligotrophic Lake Stechlin. The strai ns STL1 and STL4 were obtained from the oxic uppermost layer, while st rain STL6 was isolated from the anoxic zone in 20 to 30 mm depth. The isolates showed a striking morphological feature in tapering off at on e end of the cell. Physiological characteristics related them to the g enus Desulfovibrio. They contained desulfoviridin. H-2, formate, pyruv ate, lactate, and fumarate were utilized with sulfate, sulfite, thiosu lfate, or elemental sulfur as electron accepters. All isolates were ab le to reduce oxygen and survived 120 h of aeration. However, aerobic g rowth was not observed. The isolates were psychrotolerant, and grew wi th rates of up to 0.29 d(-t) at 4 degrees C. Analysis of the 16S rDNA confirmed that the strains belong to the genus Desulfovibrio. However, they were nor: closely related to any known member of this genus and formed a new cluster with at least two new species. Strain STL1 and ST L4, exhibiting 99.7% sequence similarity in 16S rRNA, are proposed as the new species Desulfovibrio cuneatus sp. nov., while strain STL6 is assigned to the new species Desulfovibrio litoralis sp. nov.