Identification of A Novel Arsenic Resistance Transposon Nested in A Mercury Resistance Transposon of sp. MB24.

A novel Tn1-like transposon designated as Tn1 was identified from mercury resistant isolated from Minamata Bay sediment. Two adjacent operon-like gene clusters, and , flanked by a pair of 78-bp inverted repeat sequences, which resulted in a 13.8-kbp transposon-like fragment, were found to be sandwiched between two transposable genes of the Tn1-like transposon of a mercury resistant bacterium, sp. MB24. The presence of a single transcription start site in each cluster determined by 5'-RACE suggested that both are operons. Quantitative real time RT-PCR showed that the transcription of the genes contained in each operon was induced by arsenite, while responded to arsenite more sensitively and strikingly than did. Further, arsenic resistance complementary experiments showed that the operon conferred arsenate and arsenite resistance to an -knocked out host, while the operon only raised arsenite resistance slightly. This transposon nested in Tn1 was designated as Tn1. Multi-gene cluster blast against bacteria and whole genome sequence databases suggested that Tn1 is the first case of a Tn1-like transposon combined with an arsenic resistance transposon. The findings of this study suggested that Tn1-like transposons could recruit other mobile elements into its genetic structure, and subsequently cause horizontal dissemination of both mercury and arsenic resistances among in Minamata Bay.