Water Relations of Erwinia chrysanthemi: Intracellular and Extracellular Pectate Lyase Production

When Erwinia chrysanthemi was grown in a sodium polypectate/yeast extract/salts medium adjusted with sorbitol to water activity (aw ) values of 0·990 and 0·980, extracellular pectate lyase (PL) production was repressed, whereas intracellular PL levels were not affected. Inorganic solutes (NaCl. LiCl, KCl, Na2SO4 and a NaCl/KCl/Na2SO4 mixture) at 0·990 aw strongly stimulated the intracellular levels of PL (6-to 17-fold greater than the control), whereas extracellular levels were only slightly increased. Intra-and extracellular PL levels were not affected by LiCl, NaCl and KCl at 0·995 a w. A NaCl/sorbitol mixture (0·990 a w) completely inhibited extracellular but not intracellular PL production. Lowering of the aw of cultures during mid-exponential growth phase with NaCl (0·990 a w) resulted within 30 min in a 70-fold increase in intracellular PL activity. When sorbitol was used in similar experiments, extracellular PL production was inhibited to a greater extent than intracellular levels.