Phase Transitions in the Membrane of a Marine Bacterium, Pseudomonas BAL‐31

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Abstract
An unsaturated fatty acid auxotroph, strain UFA, isolated from the marine pseudomonad Pseudomonas BAL-31, host cell of the lipid-containing phage 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 ESR using a nitroxide spin probe. Membranes prepared from strain UFA grown in cis16:1 or trans16:1 showed 1 transition at 9.4.degree. C and 12.4.degree. 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 1 transition at .apprxeq. 12.degree. C, but there was no clear cut phase transition using extracted lipids. Replication of phage PM2 took place below the transition temperature of the membrane lipids in the case where strain UFA was grown in trans16:1. Other cases were not studied.