Characterization of a new thermophilic sulfate-reducing bacterium

Abstract

A thermophilic sulfate-reducing vibrio isolated from thermal vent water in Yellowstone Lake, Wyoming, USA is described. The gram-negative, curved rod-shaped cells averaged 0.3 μm wide and 1.5 μm long. They were motile by means of a single polar flagellum. Growth was observed between 40° and 70 °C with optimal growth at 65 °C. Cultures remained viable for one year at 27 °C although spore-formation was not observed. Sulfate, thiosulfate and sulfite were used as electron acceptors. Sulfur, fumarate and nitrate were not reduced. In the presence of sulfate, growth was observed only with lactate, pyruvate, hydrogen plus acetate, or formate plus acetate. Pyruvate was the only compound observed to support fermentative growth. Pyruvate and lactate were oxidized to acetate. Desulfofuscidin and c-type cytochromes were present. The G+C content was 29.5 mol%. The divergence in the 16S ribosomal RNA sequences between the new isolate and Thermodesulfobacterium commune suggests that these two thermophilic sulfate-reducing bacteria represent different genera. These two bacteria depict a lineage that branches deeply within the Bacteria domain and which is clearly distinct from previously defined phylogenetic lines of sulfate-reducing bacteria. Strain YP87 is described as the type strain of the new genus and species Thermodesulfovibrio yellowstonii. Yellowstone Lake (Wyoming, USA) is located within one of the most tectonically active regions in the world (Klump et al. 1988; Remsen et al. 1990). Hydrothermal springs, hot gas fumaroles and elevated substrata temperatures have been observed within the lake itself (e.g., Remsen et al. 1990). Hydrothermal vent waters were reported to be anoxic, high in dissolved nutrients relative to the lake water and to have temperatures in excess of 80 °C (Klump et al. 1988; Remsen et al. 1990). Sulfate concentrations averaged 380 μM in vent waters and 80 μM in bulk lake water (Klump et al. 1988; Remsen et al. 1990). On the basis of on these physical and chemical characteristics, and the observation (e.g., Zeikus et al. 1983) that microbial sulfate reduction is prevalent in the thermal aquatic environments of Yellowstone National Park, we hypothesized that hydrothermal vent waters in Yellowstone Lake could support the growth of thermophilic sulfate reducers.

Here we describe the general characteristics of a new thermophilic sulfate reducing bacterium, Thermodesulfovibrio yellowstonii, which was isolated from hydrothermal vent water in Sedge Bay of Yellowstone Lake, Wyoming, USA. In addition, we report on the phylogenetic relationship of this new isolate with other thermophilic and mesophilic sulfate-reducing bacteria.