Effect of pH on the proportions of polar lipids, in chemostat cultures of Bacillus subtilis.

Significant changes in the relative proportions of the individual polar lipids of two strains of Bacillus subtilis were observed when the pH of their chemostat cultures was varied. In phosphate- and magnesium-limited cultures of B. subtilis var. niger NCIB 8058. lysylphosphatidylglycerol was present in higher proportions at low pH (5.1) than at neutral pH. With magnesium-limited cultures of this strain harvested at pH 8.0, lysylphosphatidylglycerol and phosphatidylethanolamine were not detected. Phosphate-limited cultures of B. subtilis NCIB 3610 contained no phosphatidylethanolamine or lysylphosphatidylglycerol at neutral pH, but at low pH (5.1) both these lipids were present in substantial proportions. The proportions of phosphatidylglycerol in actively dividing cells of chemostat cultures of bacilli were always greater than those of lysylphosphatidylglycerol. The reverse is commonly found in batch cultures of bacilli and staphylococci harvested at low pH. Changes in the proportions of the other polar lipids present in these bacilli (diphosphatidylglycerol and diglucosyl diacylglycerol) with pH were also noted. Certain cultures of both strains of B. subtilis contained small proportions of a peptidolipid.