The cells were collected by centrifugation at 4,000 × g for 10 min at 23°C, and the cell membranes were harvested by dissolving the pellets thoroughly in 3 ml diethyl ether-heptane (1:1) acidified with 2.5 M sulfuric acid. Following centrifugation at 500 × g for 5 min at 23°C, the upper organic phase was collected for total fatty acid methyl ester (FAME) analysis. FAMEs were generated and analyzed according to the method of Badings and Dejong (3).