TRANSMONOENOIC AND POLYUNSATURATED FATTY-ACIDS IN PHOSPHOLIPIDS OF A VIBRIO SPECIES OF BACTERIUM IN RELATION TO GROWTH-CONDITIONS

A Vibrio species of bacterium known to contain the polyunsaturated fat ty acid 20:5n-3 was grown in both freshwater and seawater media at 5 a nd 20-degrees-C and examined for adaptive changes in lipid composition . Phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), togethe r with a smaller proportion of nonesterified fatty acids (NEFA), compr ised almost all the lipid under all growth conditions examined. Temper ature had a more pronounced effect than the salinity of the medium on lipid composition. The proportion of PE in total lipid was always high er at 5 than at 20-degrees-C. Conversely, the proportion of NEFA was l ower at 5 than 20-degrees-C whereas that of PG was not altered. The le vels of saturated fatty acids in total lipid, PE and PG were all decre ased by growth at 5-degrees-C. No differences were observed with respe ct to growth temperature in the levels of cis 16:ln-7, the principal m onoenoic fatty acid in both PE and PG. Trans 16:1n-7 was found to comp rise 12.8-15.2% of fatty acids in PE and PG of bacteria grown at 5-deg rees-C but only 4.4-8.5% of phospholipid fatty acids in bacteria cultu red at 20-degrees-C. Regardless of medium composition, a reduction in growth temperature from 20 to 5-degrees-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 of trans 16:1n-7 and 20:5n- 3 is unique to this Vibrio species of bacterium. The increased proport ions of both these fatty acids with decreasing temperature suggest tha t they have a role in retailoring biomembrane phospholipids during tem perature acclimation of the bacterium.