Lipid composition of aminopterin-resistant and sensitive strains of Streptococcus pneumoniae. Effect of aminopterin inhibition.

The polar lipids of Streptococcus pneumoniae wild type and aminopterin-resistant strains were analysed. The membrane contained only two acid phospholipids, phosphatidylglycerol and cardiolipin, and a large amount of two glycolipids, glucosyldiglyceride and galactosylglucosyldiglyceride. The unsaturated acyl chains ranged from 58 to 87% of total fatty acids, depending on the strain and on growth conditions. No relation could be established between aminopterin resistance and polar lipid or fatty acid compositions. However, in the presence of bacteriostatic concentrations of aminopterin, the wild type and the resistant mutant did not have the same behavior. The resistant strain maintained its fatty acid composition and a normal [32P]phosphate distribution among phospholipids while the wild type shifted to a higher content in unsaturated fatty acids and to a high relative cardiolipin labelling. Such a differencein [32P] distribution was not observed when bacteriostatic concentrations of chloramphenicol were used, or when growth was stopped after amino acid deprivation induced by high concentrations of isoleucine. The biochemical basis of the aminopterin resistant character of the amiA mutants are not yet well understood but the present study establishes that the mutation confers a certain insensitivity of the lipid metabolism to aminopterin.