Re-evaluation of osmotic effects as a general adaptative strategy for bacteria in sub-freezing conditions

We studied the molecular mechanisms of adaptation of a Siberian psychrophil ic bacterial strain. Upon adaptation to 4 degreesC from 24 degreesC, the ma jor changes observed were in the membrane and cell surface chemistry. There was no evidence for the formation of so-called 'compatible metabolites' th at are thought to be responsible for the survival at very low to sub-freezi ng temperatures. The membrane fatty acids were shorter with an increased am ount of unsaturation in the 4 degreesC cells compared To the 24 degreesC ce lls. The absence of a significant amount of phosphorylation in the membrane lipids at 4 degreesC compared to the levels at 24 degreesC was another sig nificant difference, At 4 degreesC, the cell size was reduced in volume by a factor of similar to 14 compared to its size at 24 degreesC. The polar po lysaccharide capsular layer was also significantly reduced, There were no s ignificant changes in the protein profiles indicating that antifreeze prote ins were not bring produced. The results obtained here are consistent with observations and established theories and principles on and about the behav ior of water in confined spaces, These indicate that ordering effects, surf ace charge and polarity are the key determinants of the freezing point and the type of ice structure that will be formed when water is confined to an area of the size of a bacterial cell. (C) 2001 Elsevier Science B.V. All ri ghts reserved.