EFFECTS OF OCTANE ON THE FATTY-ACID COMPOSITION AND TRANSITION-TEMPERATURE OF PSEUDOMONAS-OLEOVORANS MEMBRANE-LIPIDS DURING GROWTH IN 2-LIQUID-PHASE CONTINUOUS CULTURES

Growth of Pseudomonas oleovorans GPol in continuous culture containing a bulk n-octane phase resulted in changes of the fatty acid compositi on of the membrane lipids. Compared to citrate-grown cells, the ratio of C-18 to C-16 fatty acids and the ratio of unsaturated to saturated fatty acids increased as a result of growth on octane. Trans-unsaturat ed fatty acids, which are rarely found in bacteria, were formed during continuous growth of P. oleovorans on octane. Moreover, the mean acyl chain length and unsaturated fatty acids also increased as the growth rates increased both in octane-grown and citrate-grown cells. Differe ntial scanning calorimetry measurements of extracted lipids showed the transition temperature of membrane lipids from octane-grown cells inc reased from about 24 degrees C to 32 degrees C as the growth rate incr eased, whereas cells grown on citrate showed a constant transition tem perature of about 6 degrees C at all growth rates tested indicating a decrease of membrane lipid fluidity in octane-grown cells. Because alk anes are known to increase bilayer fluidity by intercalating between l ipid fatty acyl chains, the increased transition temperature of the li pids of cells grown on octane may be a physiological response of P. ol eovorans to compensate for the direct effects of octane on its cellula r membranes.