The influence of pH on the cellular composition of Yersinia enterocolitica

Six strains of Yersinia enterocolitica were grown at pH 5.0, 7.0 and 9.0. Variations in the pH of the environment altered the amount of total lipid present, as well as the relative percentages of the individual fatty acids and phospholipids.

A higher amount of total lipid was observed at acidic pH's with a lesser amount at alkaline pH's. The fatty acid analysis of strains E752, IP383 and 190-34/IB showed a decrease in the relative percentage of unsaturated fatty acids in acidic environments. All strains tested except E752 and IP383 showed a decrease in the relative percentage of the branched forms when the organism was grown in acidic environments. Cultures grown at pH 5.0 also tended to have a higher relative percentages of cyclopropane fatty acids. The phospholipid analysis showed large increases in the relative percentage of phosphatidyl ethanolamine at higher pH's and increases in the relative percentage of phosphatidyl serine at low pH's. (It is not known if the amount of unsaturated hydrocarbons effected the relative amounts of phospholipid detected due to the nature of the HPLC-UV analysis.) Assuming that unsaturated fatty acids were equitably incorporated into the hydrocarbon tails of the phospholipids, it would appear that the cell envelope can adapt the biosynthesis of phospholipids to environmental pH.