ERWINIA-CHRYSANTHEMI AT HIGH OSMOLARITY - INFLUENCE OF OSMOPROTECTANTS ON GROWTH AND PECTATE LYASE PRODUCTION

The mechanism of osmotic stress adaptation was investigated in the phy topathogen Erwinia chrysanthemi. Growth of the bacterium was inhibited by elevated medium osmolarity, and exogenous glycine betaine, proline , ectoine or pipecolate permitted recovery of growth at inhibitory osm olarity. Osmoprotectants were taken up by transporters induced by elev ated osmolarity, and their level of accumulation within the cell was d ependent on the osmolarity of the growth medium. The influence of osmo larity and osmoprotectants on the production of pectate lyases (PLs) w as investigated. Increased medium osmolarity resulted first in an indu ction of PL activity, followed by a shift to the basal level at higher osmolyte concentrations. This induction was reversed by osmoprotectan ts in the medium. The increased PL activity was attributed in part to the induced transcription of the main PL gene, pelE, and all the osmop rotectants that were analysed were found to prevent pelE induction. PL activity was partially inhibited in vitro by high ionic strength but not by elevated concentrations of sugars, and the addition of osmoprot ectants at 1 mM had no effect on PL activity in vitro.