A Novel Gene Cluster soxSRT Is Essential for the Chemolithotrophic Oxidation of Thiosulfate and Tetrathionate by Pseudaminobacter salicylatoxidans KCT001

Chemolithotrophic sulfur oxidation (Sox) in the α-proteobacterium Pseudaminobacter salicylatoxidans KCT001 was found to be governed by the gene cluster soxSRT–soxVWXYZABCD. Independent transposon-insertion mutations in the genes soxB, soxC, soxD, and also in a novel open reading frame (ORF), designated as soxT, afforded revelation of the entire sox locus of this bacterium. The deduced amino acid sequence of the novel ORF soxT comprised 362 residues and exhibited significant homology with hypothetical proteins of diverse origin, including a permease-like transport protein of Escherichia coli. Two contiguous ORFs, soxR and soxS, immediately preceded the soxT gene. The gene cluster soxSRT was located upstream of soxVWXYZABCD and was transcribed divergently with respect to the latter. Chemolithotrophic utilization of both thiosulfate and tetrathionate was observed to have been impaired in all of these Sox⁻ mutants, implicating the involvement of the gene cluster soxSRT–soxVWXYZABCD in the oxidation of both thiosulfate and tetrathionate. Pradosh Roy Deceased