Isolation and Characterization of Arsenite-Oxidation Bacteria From Arsenic-contaminated Groundwater in Blackfoot Disease Region in Taiwan

Arsenic is an environmental carcinogen of toxicological concern. Although arsenic is generally toxic to life, it has been demonstrated that some microorganisms can use arsenic compounds as electron donors, electron acceptors, or possess arsenic detoxification mechanisms. Increasing evidences suggest that the biogeochemical cycle of arsenic is significant dependent on microbial transformations which affect the distribution and the mobility of arsenic species in the environment. However, the roles of the bacteria in the arsenic cycles are yet to be fully elucidated. In this study, we isolate As(V)-As(III) redox bacteria using arsenic-contaminated groundwater in Blackfoot disease region in Taiwan under oxic condition. Two hundred and nineteen arsenic-resistant heterotrophic bacterial strains were isolated. Analysis of the 16S rRNA gene sequence of some bacteria revealed that some of bacteria have been indicated involving in arsenic transformation, while others have not been reported to be associated with arsenic transformation. Of these isolated bacteria, one designated as L7506 was selected for further investigation. Strain L7506 is a Gram- negative, straight to curved rod, and motile bacteria. It belongs to genus Bosea based on 16S rRNA sequence analysis. The optimal growth condition was at pH 6-7, 37'C in LB medium. Moreover, it was able to grow in the presence of 100mM arsenate. L7506 began to significantly oxidize arsenite (2mM) to arsenate after 3-day incubation and complete the oxidation process after 10-day incubation. To further explore the genetic basis for the regulation of arsenite oxidation, transposon Tn5 mutagenesis was used to identify genetic determinants required for arsenite oxidation in L7506 and it is in progress. Results from this study show that diverse bacteria were isolated from arsenic-contaminated groundwater in Blackfoot disease region in Taiwan. The identified As(III)-oxidizing bacteria may be potentially used for bioremediation of arsenic-contaminated groundwater. Keywords: arsenite-oxidation, groundwater, bioremediation