Effects of octane on the fatty acid composition and transition temperature of Pseudomonas oleovorans membrane lipids during growth in two-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 composition of the membrane lipids. Compared to citrate-grown cells, the ratio of C18 to C16 fatty acids and the ratio of unsaturated to saturated fatty acids increased as a result of growth on octane. Trans-unsaturated 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. Differential scanning calorimetry measurements of extracted lipids showed the transition temperature of membrane lipids from octane-grown cells increased from about 24°C to 32°C as the growth rate increased, whereas cells grown on citrate showed a constant transition temperature of about 6°C at all growth rates tested, indicating a decrease of membrane lipid fluidity in octane-grown cells. Because alkanes are known to increase bilayer fluidity by intercalating between lipid fatty acyl chains, the increased transition temperature of the lipids of cells grown on octane may be a physiological response of P. oleovorans to compensate for the direct effects of octane on its cellular membranes.

Pseudomonas oleovorans as a source of bioplastics : production and characterization of poly(3-hydroxyalkanoates)

Poly(3-hydroxyalkanoates) WAS) are biological polyesters which are accumulated by a wide range of bacteria under conditions of excess carbon source and limiting concentrations of an essential nutrient such as nitrogen. Poly(3-hydroxybutyrate) (PHB), the best known example of these biopolymers has been extensively studied since its discovery in 1926. Only recently, it has been considered as a possible biodegradable substitute for conventional nondegradable plastics. PHI3 has long been thought the only bacterial polyester, until in the early 1980's a PHB resembling polymer was discovered in Pseudomom oleovorans after growth on n-octane. The P. oleovorans PHA distinguished itself from PHB by having longer pendant groups attached to a similar backbone. Moreover, it was found that the length of the pendant group was dependent on the carbon source used to grow the organism. Thus, the PHA-synthesizing system of P. oleovorans can be used to produce a range of PHAs. To be commercially interesting in the future, this novel class of polymers has to satisfy two important conditions: 1. besides the expected biodegradable properties, the physical and mechanical properties of any of the PHAs must be promising, and 2. PHAs must be available in large quantities. In this respect, we have examined some physical properties of a number of PHAs isolated from P. oleovorans and studied the production of one of them (the 'octane-derived' polymer) in fed-batch and continuous culture systems.