Osmotically induced intracellular trehalose, but not glycine betaine accumulation promotes desiccation tolerance in Escherichia coli

Trehalose considerably increased the tolerance of Escherichia coil to air d rying, whether added as an excipient prior to drying or accumulated as a co mpatible solute in response to osmotic stress. The protective effect of exo genously added trehalose was concentration dependent, up to a threshold val ue of 350 mM. However, trehalose alone cannot explain the intrinsically gre ater desiccation tolerance of stationary compared to exponential phase E. c oli cells, although their tolerance was also enhanced by exogenous or endog enously accumulated trehalose. In contrast, glycine betaine whether added a s an excipient or accumulated intracellularly had no influence on desiccati on tolerance. These data demonstrate that the protection provided by compat ible solutes to cells subjected to desiccation differs from that during osm otic stress, due to the much greater reduction in available cell water. The protective effects of trehalose during: desiccation appear to be due to it s stabilising influence on membrane structure? its chemically inert nature and the propensity of trehalose solutions to form glasses upon drying, prop erties which are not shared by glycine betaine. (C) 1999 Federation of Euro pean Microbiological Societies. Published by Elsevier Science B.V. All righ ts reserved.