Model for the mechanism controlling the expression of competent state in Pneumococcus cultures.

Tomasz, Alexander (The Rockefeller University, New York, N.Y.). Model for the mechanism controlling the expression of competent state in pneumococcus cultures. J. Bacteriol. 91:1050-1061. 1966.-The phenotypic expression of competence allowing the cells to absorb genetically active deoxyribonucleic acid molecules from their environment was examined in pneumococcal cultures growing under a variety of environmental conditions. The most important single parameter affecting the time course of this expression process was found to be the cell concentration. Constant high levels of competence could be maintained in cultures growing in a continuous-dilution device. The expression of competence seems to occur through a specific induction process "catalyzed" by a macromolecular cell product-the activator substance. Under most growth conditions, the availability of endogenous activator seems to limit the expression of competence. An "autocatalytic" production of activator ensues during the activation of cells to the competent state. Evidence is presented for physiological influences affecting the cell's capacity to react with the activator. A physiological model is proposed for the control of the competent state in pneumococcus.