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

Dipartimento di Biotecnologie Agrarie, Sez. Microbiologia, Università degli Studi di Firenze, Piazzale delle Cascine 24, 50144 Firenze, Italy

Correspondence
Carlo Viti
carlo.viti{at}unifi.it

Pseudomonas corrugata 28 is a Cr(VI)-hyper-resistant bacterium. A Cr(VI)-sensitive mutant was obtained by insertional mutagenesis using EZ-Tn5 <R6Kori/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.

The GenBank/EMBL/DDBJ accession number for the P. corrugata 28 genes characterized in this paper is EU276969.

Supplementary tables of primers and oscA homologues, and a supplementary figure showing the genetic arrangement downstream of oscA homologues, are available with the online version of this paper.