UC Santa Cruz

Microorganisms play a significant role in environmental arsenic cycling. The most recent discovery to the ever growing collection of known arsenic metabolisms is photosynthesis-linked arsenite oxidation (photoarsenotrophy). However, it is poorly understood and has only been identified in thermal springs on Paoha Island of Mono Lake, CA. The arsenite oxidase ArxA is thought to be responsible for the oxidation of arsenite in photoarsenotrophy. However, the first and only isolated photoarsenotroph, Ectothiorhodospira sp PHS-1, has not proven amenable to genetic manipulations, making genetic confirmation impossible. Water, sediment, and tufa collected from Big Soda Lake and Mono County were used for enrichment culturing and functional gene analyses. arxA-specific primers successfully amplified products from 15 out of 18 environmental samples, and cloned products show high homology to existing arxA-like sequences. Strains containing arxA-like sequences and capable of arsenite oxidation belonging to the genera Ectothiorhodospira and Halomonas were isolated. This work demonstrates that arxA sequences and photoarsenotrophs can also be found in Big Soda Lake, NV, and presents two novel arxA-containing, arsenite-oxidizing strains: the chemoautotroph Halomonas sp. BSL-1 and the photoarsenotroph Ectothiorhodospira sp. BSL-9.