Effect of temperature and salinity stress on growth and lipid composition of Shewanella gelidimarina

The maximum growth temperature, the optimal growth temperature, and the est imated normal physiological range for growth of Shewanella gelidimarina are functions of water activity (a(w)) which can be manipulated by changing th e concentration of sodium chloride. The growth temperatures at the boundari es of the normal physiological range for growth were characterized by incre ased variability in fatty acid composition, Under hyper- and hypoosmotic st ress conditions at an a(w) of 0.993 (1.0% [wt/vol] NaCl) and at an a(w) of 0.977 (4.0% [wt/vol] NaCl) the proportion of certain fatty acids (monounsat urated and branched-chain fatty acids) was highly regulated and was inverse ly related to the growth rate over the entire temperature range. The physic al states of lipids extracted from samples grown at stressful a(w) values a t the boundaries of the normal physiological range exhibited no abrupt gel- liquid phase transitions when the lipids were analyzed as liposomes, Lipid packing and adaptational fatty acid composition responses are clearly influ enced by differences in the temperature-salinity regime, which are reflecte d in overall cell function characteristics, such as the growth rate and the normal physiological range for growth.