Biogenic Mineral Production by a Novel Arsenic-metabolizing Thermophilic Bacterium from the Alvord Basin, Oregon

The Alvord Basin in southeast Oregon contains a variety of hydrothermal features which have never been microbiologically characterized. A sampling of Murky Pot (61 degrees C; pH 7.1) led to the isolation of a novel arsenic-metabolizing organism (YeAs) which produces an arsenic sulfide mineral known as beta-realgar, a mineral that has not previously been observed as a product of bacterial arsenic metabolism. YeAs was grown on a freshwater medium and utilized a variety of organic substrates, particularly carbohydrates and organic acids. The temperature range for growth was 37 to 75 degrees C (optimum, 55 degrees C), and the pH range for growth was 6.0 to 8.0 (optimum, pH 7.0 to 7.5). No growth was observed when YeAs was grown under aerobic conditions. The doubling time when the organism was grown with yeast extract and As(V) was 0.71 h. Microscopic examination revealed Gram stain-indeterminate, non-spore-forming, nonmotile, rod-shaped cells, with dimensions ranging from 0.1 to 0.2 microm wide by 3 to 10 microm long. Arsenic sulfide mineralization of cell walls and extracellular arsenic sulfide particulate deposition were observed with electron microscopy and elemental analysis. 16S rRNA gene analysis placed YeAs in the family Clostridiaceae and indicated that the organism is most closely related to the Caloramator and Thermobrachium species. The G+C content was 35%. YeAs showed no detectable respiratory arsenate reductase but did display significant detoxification arsenate reductase activity. The phylogenetic, physiological, and morphological characteristics of YeAs demonstrate that it is an anaerobic, moderately thermophilic, arsenic-reducing bacterium. This organism and its associated metabolism could have major implications in the search for innovative methods for arsenic waste management and in the search for novel biogenic mineral signatures.