Tuesday, November 14, 2006 - 5:45 PM
179-3

Bacterial Arsenite Oxidase Genes Detected in Soil, Sediment and Geothermal Environments.

William Inskeep1, Richard Macur1, Natsuko Hamamura1, Deanne Masur1, W. Peyton Taylor1, T. P. Warelow2, S.A. Ward3, and J.M. Santini3. (1) Montana State Univ, Land Resources and Environmental Sciences, Bozeman, MT 59717, (2) La Trobe Univ, Dept of Microbiology, Melbourne, Victoria, 3068, Australia, (3) Univ College London, Dept of Biology, London, WC1E 6BT, United Kingdom

Arsenic is an abundant and dynamic trace element distributed in numerous environmental contexts throughout the globe. The microbial transformations of As have been studied intensively during the past decade in part due to recent water quality crises in Bangladesh, India, and southeast Asia. Microorganisms possess numerous regulatory genes responsible for various transformations of As, including reduction, methylation and oxidation, all of which contribute to the fate, transport and biogeochemical cycling of As. The oxidation of arsenite is commonly observed in soil, sediment and natural waters, and several arsenite-oxidizing microorganisms have been isolated and characterized. In many cases, microorganisms do not appear to gain energy from the oxidation of arsenite, although several arsenite chemolithotrophs have been isolated. The arsenite oxidases (AroA) implicated in chemolithotrophic organisms are reasonably homologous to other known arsenite oxidases that are thought to function as a detoxification strategy (AsoA/AoxB). The primary goal of our work was to describe the distribution and importance of aroA-like genes across different geochemical environments in the USA and Australia. Extracted DNA from As-contaminated soils, sediments and geothermal springs was used to amplify bacterial aroA-like genes using primers designed around known and putative aroA genes. To our knowledge, this is the first report of successful amplification of aroA-like genes from natural systems. In total, over 160 different aroA-like clones were sequenced. Furthermore, RNA extraction followed by reverse transcriptase (RT)-PCR showed that aroA-like genes are being expressed when arsenite is rapidly oxidized in geothermal environments and in pure culture isolates. Our results suggest that aroA-like genes are widely distributed among microorganisms, and are ecologically important in numerous environments across the globe. Although questions remain regarding the physiological role of arsenite oxidases, the distribution of aroA-like genes suggests that microbial oxidation of arsenite is a critical component in the global cycling of As.

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