The mechanism of osmotic stress adaptation was investigated in the phytopathogen . Growth of the bacterium was inhibited by elevated medium osmolarity, and exogenous glycine betaine, proline, ectoine or pipecolate permitted recovery of growth at inhibitory osmolarity. Osmoprotectants were taken up by transporters induced by elevated osmolarity, and their level of accumulation within the cell was dependent on the osmolarity of the growth medium. The influence of osmolarity and osmoprotectants on the production of pectate lyases (PLs) was investigated. Increased medium osmolarity resulted first in an induction of PL activity, followed by a shift to the basal level at higher osmolyte concentrations. This induction was reversed by osmoprotectants in the medium. The increased PL activity was attributed in part to the induced transcription of the main PL gene, , and all the osmoprotectants that were analysed were found to prevent induction. PL activity was partially inhibited by high ionic strength but not by elevated concentrations of sugars, and the addition of osmoprotectants at 1 mM had no effect on PL activity .


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