Characterization of the Erwinia chrysanthemi osmoprotectant transporter gene ousA

Growth of Erwinia chrysanthemi in media of elevated osmolarity can be achieved by the uptake and accumulation of various osmoprotectants. This study deals with the cloning and sequencing of the ousA gene-encoded osmoprotectant uptake system A from E. chrysanthemi 3937. OusA belongs to the superfamily of solute ion cotransporters. This osmotically inducible system allows the uptake of glycine betaine, proline, ectoine, and pipecolic acid and presents strong similarities in nucleotide sequence and protein function with the proline/betaine porter of Escherichia coli encoded by proP. The control of ousA expression is clearly different from that of proP. It is induced by osmotic strength and repressed by osmoprotectants. Its expression in E. coli is controlled by H-NS and is rpoS dependent in the exponential phase but unaffected by the stationary phase.