Isolation and Molecular Characterization of Arsenate Respiration and Resistance Bacterial Strain W2 from Arsenic-Contaminated Groundwater in Taiwan

Arsenic is a naturally occurring element that is found in many environments. The contamination of groundwater with arsenic is a major concern to public health from local to international. Arsenic groundwater problems in Taiwan were first recognized during the 1960s and then Taiwan becomes the classic area for the study of Blackfoot disease and a variety of other typical problems including cancers. However, both the mineral sources of arsenic and the biogeochemistry of the groundwater of arsenic are poorly defined in Taiwan. Increasing evidences suggest that the biogeochemical cycle of arsenic is significantly dependent on microbial transformations which affect the distribution and the mobility of arsenic species in the environment. In this study, we isolated and molecular characterized the relationship between arsenate respiration and arsenic resistance bacterial strains. Of these isolated strains, strain W2 was selected for further investigation. Strain W2 is a mixotrophic microbe, and the optimal temperature for growth was 37℃. Strain W2 was able to grow both under aerobic and anaerobic conditions. Resistance tests showed that strain W2 could resist high concentrations of arsenate and arsenite when grown in LB medium. Arsenic transformation analysis showed that strain W2 could completely reduced 2 mM (150 ppm) of arsenate to arsenite within 42 hours in LB under anaerobic condition, and within 10 days in MSM (minimal salts medium) medium supplemented with 10 mM glucose under anaerobic condition. In addition, strain W2 growth was accompanied with arsenate reduction. Moreover, thiosulfate reductase PhsA and ArsR genes were amplified by PCR reaction, suggesting that strain W2 contains both dissimilatory arsenate reduction and arsenic detoxification mechanisms. Furthermore, denaturing gradient gel electrophoresis analysis showed that diversed microbial was present in arsenic-contaminated groundwater samples of different wells in Taiwan.