Large decreases in membrane phosphatidylethanolamine and diphosphatidylglycerol upon mutation to duramycin resistance do not change the protonophore resistance of Bacillus subtilis.

Duramycin-resistant mutant strains were selected from wild-type Bacillus subtilis (BD99) and its protonophore-resistant mutant derivative, strain AG1A3. Analyses of the membranes of the duramycin-resistant mutants showed that they had little or no phosphatidylethanolamine and diphosphatidylglycerol as determined by chemical detection after thin-layer chromatography. Small amounts of these phospholipids must remain in the mutant strains, however, because during studies of incorporation of exogenous, radioactive fatty acids, label associated with palmitoleic acid was found in chromatographic positions that corresponded to the expected positions of phosphatidylethanolamine and diphosphatidylglycerol. The duramycin-resistant strains both showed elevated levels of phosphatidylglycerol and aminoacyl(lysyl)phosphatidylglycerol. The duramycin-resistant derivative of protonophore-resistant AG1A3 (AG1A3-DR4), but not that of the wild type, also showed a decreased content of neutral relative to polar lipid in the membrane. The composition of neutral lipid in that strain was higher in free fatty acids and lower in 1,2-diacylglycerol than its parent strain. AG1A3-DR4 also contained appreciable levels of lysophosphatidylethanolamine and somewhat elevated diglycosyldiacylglycerol relative to the other strains in the study. The protonophore resistance of AG1A3 was unaltered by mutation to duramycin resistance. Nor was there any change in the efficacy of exogenous palmitoleic acid in diminishing the protonophore resistance of AG1A3-DR4. This phenomenon persists upon dramatic reduction in the content of phosphatidylethanolamine and diphosphatidylglycerol even though those phospholipids are normally the preferred sites of incorporation of the exogenous unsaturated fatty acids that mediate the effect.