The chromosomal arsenic resistance genes of Sulfobacillus thermosulfidooxidans

Arsenic resistance genes were isolated from the moderately thermophilic, Gram-positive iron and sulfur-oxidizing bacterium, Sulfobacillus thermosulfidooxidans. Only arsR and arsB genes were present and attempts to identify an arsC using degenerate PCR primers or Trx- or Grx-dependent arsC genes as probes in Southern hybridization experiments were unsuccessful. Although enhanced resistance to arsenite was not detected when the ars genes were cloned in Escherichia coli, the adjacent kumamolisin-As and arsRB genes were induced by arsenite. RT-PCR experiments suggested that transcription of the cloned kumamolisin-As-like and arsRB genes is linked in E. coli, but not in S. thermosulfidooxidans. The gene order kumamolisin-As precursor, arsR and arsB is maintained among three strains of S. thermosulfidooxidans isolated from three continents. Southern hybridization using a S. thermosulfidooxidans arsB gene fragment as a probe gave a positive hybridization signal using Sulfobacillus acidophilus but not with Sulfobacillus thermotolerans genomic DNA. Comparison of partial sequence data of the arsB and 16 S rRNA genes suggested that the two types of genes have undergone a similar evolutionary history and therefore that the arsB genes were present in the ancestral Sulfobacillus before its divergence into species.