Microbial influence on arsenic speciation: In search of the origins of arsenic resistance

Early life on Earth had to cope with heat, acidity and high dissolved metal(loid) concentrations. Arsenic (As) is one metalloid enriched in geothermal waters. In order to survive toxic arsenic levels, microorganisms developed arsenic resistance mechanisms for arsenic species present at that time. Modern hot springs provide an analog to early Earth conditions in terms of temperature and dissolved arsenic concentrations. The nucleic acid data suggest a hyperthermophilic root of life, which supports the hypothesis of hot springs providing ideal conditions to investigate the evolution of microbial arsenic resistance. Geothermal pools in Wai-O-Tapu, New Zealand, with different temperature, pH and redox condition were studied for their arsenic speciation and microbial diversity. On an Eh-pH diagram, all pools plotted within the arsenite (H3AsO3) stability field. Alongside arsenite, however, HPLC-ICPMS analyses also detected arsenate, organic arsenic and unknown arsenic species, suggesting active microbial transformation of As[III] via one or more arsenic resistance mechanisms.