Tn5037, a Tn21-like mercury resistance transposon from Thiobacillus ferrooxidans

The 6645-bp mercury resistance transposon of the chemolithotrophic bacteriu m Thiobacillus ferrooxidans was cloned and sequenced. This transposon, name d Tn5037, belongs to the Tn21 branch of the Tn21 subgroup, many members of which have been isolated from clinical sources. Having the mininium set of the genes (merRTPA), the mercury resistance operon of Tn5037 is organized s imilarly to most of the Gram-negative bacteria mer operons and is closest t o that of Thiobacillus T3.2. The operator-promoter region of the mer operon of Tn5037 also has the common (Tn21/Tn501-like) structure. However, its in verted, presumably MerR protein binding repeats in the operator/promoter el ement are two base pairs shorter than in Tn21/Tn501. In the merA region, th is transposon shares 77.4, 79.1, 83.2 and 87.8% identical bases with Tn21, Tn501, T. ferrooxidans E-15, and Thiobacillus T3.2, respectively. No induci bility of the Tn5037 mer operon was detected in the in vivo experiments. Th e transposition system (terminal repeats plus gene tnpA) of Tn5037 was inac tive in Escherichia coli K12, in contrast to its resolution system (res sit e plus gene tnpR). However, transposition of Tn5037 in this host was provid ed by the tnpA gene of Tn5036, a member of the Tn21 subgroup. Sequence anal ysis of the Tn5037 res site suggested its recombinant nature.