Involvement of the oscA gene in the sulphur starvation response and in Cr(VI) resistance in Pseudomonas corrugata 28

Pseudomonas corrugata 28 is a Cr(VI)-hyper-resistant bacterium. A Cr(VI)-sensitive mutant was obtained by insertional mutagenesis using EZ-Tn5 < R6K gamma ori/KAN-2 > Tnp. The mutant strain was impaired in a gene, here named oscA (organosulphur compounds), which encoded a hypothetical small protein of unknown function. The gene was located upstream of a gene cluster that encodes the components of the sulphate ABC transporter, and it formed a transcriptional unit with sbp, which encoded the periplasmic binding protein of the transporter. The oscA-sbp transcriptional unit was strongly and quickly overexpressed after chromate exposure, suggesting the involvement of oscA in chromate resistance, which was further confirmed by means of a complementation experiment. Phenotype MicroArray (PM) analysis made it possible to assay 1536 phenotypes and also indicated that the oscA gene was involved in the utilization of organosulphur compounds as a sole source of sulphur. This is believed to be the first evidence that oscA plays a role in activating a sulphur starvation response, which is required to cope with oxidative stress induced by chromate.