Effects of fatty acids in bile on the phospholipids of Vibrio cholerae
Enteric bacteria, such as E. coli and V. cholerae, encounter the digestive secretion bile in the small intestine. Bile is composed of mainly bile acids, lecithin, bilirubin, bicarbonate ions and fatty acids. Since bile possesses detergent like activity, bacteria have evolved mechanisms to avoid its bactericidal effect. V. cholerae senses bile and activates virulence genes that mediate motility, chemotaxis and adherence in preparation for colonization. The present study identifies a difference in the phospholipid profile of V. cholerae, but not E. coli, when grown in the presence and absence of bile. Mass spectrometry analysis of crude bile showed a variety of fatty acids including several longchain and polyunsaturated fatty acids. To determine if the fatty acids in bile could be responsible for the differences in the phospholipids, E. coli and V. cholerae were grown in the presence of the individual fatty acids prior to phospholipid analysis. Growth of E. coli in fatty acids showed no significant changes in any phospholipids. However, growth of V. cholerae in fatty acids resulted in an upward shift of cardiolipin in longer chained fatty acids as well as the appearance of two species of phosphatidylethanolamine. There were also fatty acids that caused an appearance of lyso-phosphatidylethanolamine. These results demonstrate that V. cholerae can utilize a wider range of fatty acids than E. coli as reflected in membrane phospholipids. Specific long chain and polyunsaturated fatty acids are identified as being incorporated into V. cholerae phospholipids. V. cholerae is also associated with fatty acid rich marine environments. These environments include colonization of zooplankton and insect egg masses, as well as surviving in aquatic sediment. The survival advantage that this adaptation may provide is discussed.