Abstract
Two of four previously isolated autolysis-defective mutants of Streptococcus faecium (Streptococcus faecalis ATCC 9790) incorporated substantially more [14C]glycerol into lipids and lipoteichoic acid than did the parent strain. Consistent with increased accumulation of lipids and lipoteichoic acid, significantly higher levels of phosphorus were found in the corresponding fractions of the two mutant strains than in the wild type. Although the autolysis-defective mutant strains contained the same assortment of lipids as the wild type, the relative amount of [14C]glycerol incorporated into diphosphatidylglycerol increased, accompanied by a decreased fraction of phosphatidylglycerol. These results suggested that increased cellular content of two types of substances, acylated lipoteichoic acid and lipids (notably diphosphatidylglycerol), which previously had been shown to be potent inhibitors of the N-acetylmuramoylhydrolase of this species, contributed to the autolysis-defective phenotype of these mutants. Consistent with this interpretation are observations that (i) cerulenin inhibition of fatty acid synthesis increased the rates of benzylpenicillin-induced cellular lysis and that (ii) Triton X-100 or Zwittergent 3-14 treatment could reveal the presence of otherwise cryptic but substantial levels of the active form of the autolysin in cells of three of four mutants and of the proteinase-activable latent form in all four mutants.