Adaptation of Pseudomonas fluorescens to Low Levels of Water Activity Produced by Different Solutes

A culture of Pseudomonas fluorescens which grew at a minimal a(w) of 0.97 in a glucose-salts broth adjusted to that level with NaCl, KCl, or glucose, and at a(w) 0.9725 with Na(2)SO(4), was adapted to grow at lower a(w) levels produced by these solutes. Adaptation to growth at a low a(w) produced by means of one solute did not necessarily result in growth at that a(w) when another solute was employed to lower the a(w). The culture adapted to grow at a(w) 0.9650 produced by addition of glucose could grow equally well in broth adjusted to that a(w) with NaCl or KCl, but not Na(2)SO(4). NaCl and KCl permitted growth at the lowest a(w) level (0.9625), and the culture adapted in KCl did equally well in NaCl.