Resistance Determinants of a Highly Arsenic-Resistant Strain of Leptospirillum ferriphilum Isolated from a Commercial Biooxidation Tank

ABSTRACT Two sets of arsenic resistance genes were isolated from the highly arsenic-resistant Leptospirillum ferriphilum Fairview strain. One set is located on a transposon, TnLfArs, and is related to the previously identified TnAtcArs from Acidithiobacillus caldus isolated from the same arsenopyrite biooxidation tank as L. ferriphilum. TnLfArs conferred resistance to arsenite and arsenate and was transpositionally active in Escherichia coli. TnLfArs and TnAtcArs were sufficiently different for them not to have been transferred from one type of bacterium to the other in the biooxidation tank. The second set of arsenic resistance genes conferred very low levels of resistance in E. coli and appeared to be poorly expressed in both L. ferriphilum and E. coli.