Characterization of arsenic biotransformation by comamonas testosteroni I2

Arsenic, a metalloid, poses a great problem to many countries which utilizes groundwater for potable use, causing major health concerns to millions of people around the world. Although bacteria such as E. coli and S. oneidensis has been well characterised in its arsenate reductase capability, the bacteria Comamonas testosteroni I2, which is most commonly found in activated sludge in wastewater treatment plant, has not yet been well characterised. Since there is a possibility of reducing As(V) (low toxicity) to As(III) (high toxicity), it is a concern whether the presence of arsenic in wastewater would affect the toxicity of the activated sludge. In this study, the bacteria C. testosteroni I2 has been characterised and compared to E. coli K12 and S. oneidensis MR-1, in terms of its arsenic resistance in planktonic vs. biofilm states, arsenate reductase capability, and the study of gene expression in the presence of arsenate. Overall, I2’s arsenic resistance capability in biofilm state is higher than that of the planktonic state, only in As(V), but not in As(III). I2 also possesses the most efficient arsenate reductase capability (in 4h) in comparison to K12 (8h) and MR-1 (24hours). qPCR was then carried out to compare the gene expression in each of the gene copies in I2, K12 and MR-1, only to find out that I2 gives the most gene expression, which could possibly be attributed to the reductase capability performed by arsC and efflux system performed by arsB to drive out As(III) out of their cells to confer arsenic resistance. This agrees with the extraordinary performance of arsenate reductase by the gene arsC in I2.Bachelor of Engineering (Environmental Engineering