Phase transitions in the membrane of a marine bacterium, Pseudomonas BAL-31

An unsaturated fatty acid auxotroph, strain UFA, isolated from the marine pseudomonad Pseudomonas BAL-31, host cell of the lipid-containing bacte riophage PM2, was grown in media supplemented with different unsaturated fatty acids. Under these conditions the fatty acid composition of the cell could be altered drastically. The phase transition in the native membrane and in the extracted lipids was analyzed by electron spin resonance using a nitroxide spin probe. Membranes prepared from strain UFA grown in cis16:1 or trans16:1 showed one transition at 9.4 degrees C and 12.4 degrees C respectively. Extracted lipids in both cases had almost the same transition temperature as that of the intact membrane. Membranes prepared from Pseudomonas BAL-31 had one transition at approximately 12 degrees C, on the other hand there was no clear cut phase transition using extracted lipids. Replication of bacteriophage PM2 took place below the transition temperature of the membrane lipids in the case where strain UFA was grown in tran16:1. Other cases were not studied.