Temperature adaptation in Lactobacillus fermentum: interconversions of oleic, vaccenic and dihydrosterulic acids

The interchange of octadecenoic acids and dihydrosterulic acid was a response of aerobically growing Lactobacillus fermentum to changes in growth temperature. Oleic and vaccenic acid contents decreased both at temperatures below 20 degrees C and above 26 degrees C, showing mirror image behaviour, with a concomitant increase in dihydrosterulic acid. A temperature-dependent shift from vaccenic to oleic acid synthesis, and the conversion of the latter to dihydrosterulic acid was responsible for the overall change. Consequently, the degree of fatty acid unsaturation decreased at temperatures above 26 degrees C, whereas the degree of cyclization increased. The converse occurred below 20 degrees C. The relative amount of lactobacillic acid, total cellular fatty acid content, and mean fatty acid chain length were practically temperature-independent. The occurrence of oleic acid is thought to be related to aerobic growth conditions.