Autolysis and cell wall degradation in a choline-independent strain of Streptococcus pneumoniae

Streptococcus pneumoniae has an auxotrophic requirement for choline, and choline residues that incorporate into the wall and membrane teichoic acids are intimately involved with the control of autolytic phenomena of this bacterium. We report here the re-examination of the role of choline in autolytic cell wall degradation using the choline-independent S. pneumoniae strain R6Cho- recovered from a heterologous cross with DNA from Streptococcus oralis. S pneumoniae Cho- cultured in choline-free medium grew with normal generation time but formed long chains, failed to undergo stationary-phase autolysis, and was also resistant to lysis induced by deoxycholate or penicillin. Cell walls produced under these conditions had reduced phosphorus content, contained no choline residues detectable by nuclear magnetic resonance, and had reduced binding capacity for the pneumococcal autolytic amidase, and complete hydrolysis of such walls by the amidase required prolonged incubation with high concentrations of the enzyme. Addition of choline to the growth medium reversed at these phenomena. High-performance liquid chromatography analysis of amidase digests of cell walls prepared from strain R6Cho- grown with or without choline produced identical stem peptide profiles, which were also similar to that of the parental S. pneumoniae strain R6. Peptidoglycans prepared by hydrofluoric extraction of cell walls from Cho- growth with or without choline or from the parental strain R6 were uniformly susceptible to the autolytic amidase and were fully degraded to the normal family of stem peptides, indicating that, in sharp contrast to the case of cell walls, the amidase degradation of teichoic acid-free peptidoglycan did not require the presence of choline residues in the substrate.