Autolytic activity associated with competent group H streptococci

Abstract

Competent cells of group H streptococci strains Wicky and Challis autolyzed markedly when placed at 37 C in 0.05 m tris(hydroxymethyl)methyl-amino-propane sulfonic acid buffer (pH 9.0 to 9.1) containing 0.02 m 2-mercaptoethanol, whereas noncompetent cells autolyzed slightly. Autolysis of competent Wicky cells did not occur at 0 C or after the cells were heated at 100 C for 5 min. Culture fluids derived from strain Challis that contained competence factor (CF) activity did not contain lytic activity. Addition of native deoxyribonucleic acid (DNA) to competent Wicky cells caused a retardation in the rate of autolysis; ribonucleic acid and alkali-denatured DNA had less of an effect. Supernantant fluids derived from competent cell lysates lysed noncompetent Wicky cells but were inactive against cells of Hydrogenomonas eutropha, a group A Streptococcus, and against a commercial lysozyme substrate (Micrococcus lysodeikticus). This lytic activity was inactivated by heat (5 min at 100 C). Electron microscopic observations of autolyzed cells showed that autolysis occurs only at the site of cross-wall formation. A close relationship between the development of competence and autolysis is suggested by the fact that certain conditions that prevent the establishment of the competent state in Wicky populations (such as no CF, addition of CF simultaneously with chloramphenicol, and addition of trypsin-inactivated CF) also prevent autolysis. This observation emphasizes the indirect or inductive nature of CF on these processes.