Diversity of arsenic oxidizing bacteria and microbially-mediated arsenite oxidation in hot springs

Arsenic in hot springs can contribute to the contamination of surface water or groundwater. Microoganisms could oxidate arsenite (AsIII) to arsenate (AsV) which is less toxic and easier to be adsorbed. In this study, diversity... [ view full abstract ]

Arsenic in hot springs can contribute to the contamination of surface water or groundwater. Microoganisms could oxidate arsenite (AsIII) to arsenate (AsV) which is less toxic and easier to be adsorbed. In this study, diversity of arsenite oxidizing bacteria and microbially-mediated arsenic oxidization in hot springs in Tengchong of China were investigated. A total of 230 aioA clone sequences were obtained and these sequences were affiliated with four phyla: Betaproteobacteria, Alphaproteobacteria, Deinococcus-Thermus and Aquificae. Betaproteobacteria was mainly distributed in low temperature (T=27.7~42.7oC) and circumneutral or light alkaline (pH=7~9) springs; Alphaproteobacteria was mainly predominant in low pH (pH=3.3~3.6) springs; Deinococcus-Thermus and Aquificae were mainly inhabited in high temperature springs with a wide range of pH. Deinococcus-Thermus was dominant when springs had a pH within 4~8. While Aquificae dominated springs with pH > 8 or pH < 4. A new facultative chemolithoautotrophic arsenite-oxidizing bacterium TCC9-4 was obtained. This strain could grow with arsenite (AsIII) as an energy source, CO2-HCO3- as a carbon source and oxygen as the electron acceptor in a minimal salts medium. Under chemolithoautotrophic conditions, more than 90 % of AsIII (100 mg/L) could be oxidized by the strain TCC9-4 in 36 hours. The highest AsIII oxidation rates and Aio activity were found at the optimal temperature of 40 oC. Addition of 0.01 % yeast extract enhanced the growth significantly, but delayed the AsIII oxidation. The strain TCC9-4 was identified as Anoxybacillus flavithermus. The results of this study expand our current understanding of microbially-mediated arsenic oxidation in hot springs.