Trans-monoenoic and polyunsaturated fatty acids in phospholipids of aVibrio species of bacterium in relation to growth conditions

AVibrio species of bacterium known to contain the polyunsaturated fatty acid 20∶5n−3 was grown in both freshwater and seawater media at 5 and 20°C and examined for adaptive changes in lipid composition. Phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), together with a smaller proportion of nonesterified fatty acids (NEFA), comprised almost all the lipid under all growth conditions examined. Temperature had a more pronounced effect than the salinity of the medium on lipid composition. The proportion of PE in total lipid was always higher at 5 than at 20°C. Conversely, the proportion of NEFA was lower at 5 than 20°C whereas that of PG was not altered. The levels of saturated fatty acids in total lipid, PE and PG were all decreased by growth at 5°C. No differences were observed with respect to growth temperature in the levels ofcis 16∶1n−7, the principal monoenoic fatty acid in both PE and PG.Trans 16∶1n−7 was found to comprise 12.8–15.2% of fatty acids in PE and PG of bacteria grown at 5°C but only 4.4–8.5% of phospholipid fatty acids in bacteria cultured at 20°C. Regardless of medium composition, a reduction in growth temperature from 20 to 5°C also caused the proportions of 20∶5n−3 to increase from around 0.8 to 4.4% in PE and from around 4 to 20% in PG. The simultaneous occurrence oftrans 16∶1n−7 and 20∶5n−3 is unique to thisVibrio species of bacterium. The increased proportions of both these fatty acids with decreasing temperature suggest that they have a role in retailoring biomembrane phospholipids during temperature acclimation of the bacterium.