PNNL

Abstract

The Alvord Basin in southeast Oregon, USA contains a variety of hydrothermal features, which have never been microbiologically characterized. Murky Pot (61°C, pH 7.1) was selected for this study. Sampling of Murky Pot 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. Our goal was to characterize and identify YeAs based on its phylogenetic, physiological, and morphological characteristics. 16S rRNA gene analysis revealed that YeAs has 98.9% sequence similarity to that of Thermobrachium celere. YeAs was grown on a freshwater medium and could utilize a variety of organic substrates, particularly carbohydrates and organic acids. Optimum growth of the organism was seen at 55ºC, but showed growth at a range of 37° to 75°C. No growth was observed when YeAs was grown under aerobic conditions. Microscopic examination revealed Gram-indeterminate, non-spore forming, rod shaped cells. Electron microscopy and elemental analysis revealed significant arsenic sulfide mineralization of cell walls, and extracellular particulate deposition of arsenic sulfide minerals. YeAs showed no detectable respiratory arsenate reductase; however, the organism 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 signatures.