Four gram-negative bacterial species, including Escherichia coli strain B, Serratia marcescens, Pseudomonasfluorescens, and Vibrio cholerae (comma) strain NIH 41, were investigated for fatty acid content by gas-liquid chromatography involving a preparatory technique which facilitated detection of cyclopropane fatty acids. Methyl esters of fatty acids were subjected to mild catalytic hydrogenation to eliminate unsaturates. Hydrogenation was followed by bromination which removed cyclopropane acids from chromatographic profile patterns. Lactobacillic acid (cis-11,12-methyleneoctanoate) and cis-9,10-methylenehexadecanoate, previously reported in lipids of E. coli and S. marcescens, were found in small amounts in P. fluorescens but were not detected in V. cholerae.

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