Arsenate eating bacteria can mobilize arsenic from rocks and sediments, transforming it into their more toxic forms (i.e. AsIII). As a consequence, over 30 million Bangladesh are suffering from arsenicosis due to microbial mobilization of arsenic in their drinking wells. Arsenic can be important factor in the microbial ecology of lakes and subsurface waters. In Mono Lake and Searles Lake, a robust arsenic cycle drives the microbial ecology. Our most recent discovery is that As(III) can serve as the electron donor in anoxygenic photosynthesis. Through the courtesy of the DOE Joint Genome Institute, four of our arsenic metabolizing organisms (Alkalilimnicola ehrlichii, Alkaliphilus oremlandii strain OhILAs, Bacillus selenitireducens, Deltaproteobacterium MLMS-1) have had their genomes sequenced and we are completing their annotation. The genome data has allowed us to use a proteomics approach for elucidating the pathways of inorganic and organic arsenic transformation. In collaboration with Dr. Aaron Barchowsky (School of Occupational and Public Heath, U Pitt), we are investigating the change in microbial community that occurs in the lower GI tract in response to arsenic exposure. In collaboration with Dr. Partha Basu (Department of Chemistry and Biochemistry), we are studying the microbial transformation of roxarsone, an organoarsenical fed to chickens. We also continue the collaboration with Ronald Oremland (US Geological Survey) isolating and characterizing new species of bacteria (i.e., 16S rRNA), purifying and characterizing the terminal reductases and cytochromes involved in the reductive pathway, cloning and sequencing the genes encoding them, and developing biochemical and molecular probes for their detection in the environment. This work involves bacterial physiology, molecular biology, protein biochemistry, and field work. It is currently supported by NASA, NIEHS, and the NSF.