THE EFFECT OF DIFFERENT TEMPERATURES ON THE FATTY-ACID COMPOSITION OFRHIZOBIUM-LEGUMINOSARUM BV VICIAE IN THE FABA BEAN SYMBIOSIS

Fatty acid composition was determined in cells of strains CBh5 and CBp 7 of Rhizobium leguminosarum bv. viciae grown at four temperatures (10 , 15, 22 and 30 degrees C), and in bacteroids and nodules formed with faba bean (Vicia faba L.) grown at two day/night temperature regimes ( 22/15 and 15/10 degrees C). Growth temperature markedly affected the f atty acid composition of free-living bacteria in both strains studied, and both showed similar variations at each temperature. The proportio n of unsaturated fatty acids increased significantly with lowering of temperature. The major fatty acid found in bacteria and bacteroids was cis-vaccenic (C18:1(Delta 11)), which comprised up to c. 78 (bacteria ) and 56%, (bacteroids) of total fatty acids. The presence of polyunsa turated fatty acids (linoleic (C18:(Delta 9, 12)) and linolenic (C18:( Delta 9, 12, 15)) acids) was noted only in bacteroids, indicating chan ges following the differentiation of bacteria into bacteroids in the n odules. The fatty acid composition of nodules was similar to that of b acteroids, although major differences were found in their proportions. The different day/night temperature regimes had contrasting effects i n bacteroids and in nodules. In bacteroids of both strains, the propor tions of stearic (C18:0) and linoleic (C18:(Delta 9, 12)) acids decrea sed at the lower temperature regime. In nodules, the proportion of ste aric (C18:0) acid decreased, while that of linolenic (C18:3(Delta 9, 1 2, 15)) acid increased at the lower temperature regime. However, those of cis-vaccenic (C18:1(Delta 11)), linoleic (C18:(Delta 9, 12)) and p almitic (C16:0) acids increased or decreased depending on the rhizobia l strain. The proportion of unsaturated fatty acids increased with the lowering of temperatures in bacteroids of both strains, and varied in whole nodules depending on the strain. Strain CBp7 showed a greater s ymbiotic efficiency (dry matter yield) than strain CBh5 under both tem perature regimes, but no relationship was found with the proportion of unsaturated fatty acids of bacteria, bacteroids or nodules.