Effect of 8-azaguanine on the transition from vegetative growth to presporulation in Bacillus cereus.

Stahly, D. P. (University of Illinois, Urbana), V. R. Srinivasan, and H. Orin Halvorson. Effect of 8-azaguanine on the transition from vegetative growth to presporulation in Bacillus cereus. J. Bacteriol. 91:1875-1882. 1966.-The guanine analogue, 8-azaguanine (azaG), was found to inhibit sporulation of Bacillus cereus strain T when added to proliferating cells, but not to inhibit when added after the transition to presporulation. When azaG was added to vegetative cells, the growth rate was reduced, but no immediate bactericidal effect was demonstrated. Azaguanine was shown to be incorporated solely into ribonucleic acid (RNA). All of the natural purine bases and nucleosides were found to prevent azaG inhibition by blocking incorporation of the analogue into the RNA. Addition of a subinhibitory level of C(14)-azaG to proliferating cells resulted in an increase in incorporation paralleling the increase in number of cells. At the time of transition from growth to presporulation, a rapid removal of the azaG label from the cells occurred in the absence of net RNA breakdown. If differentiation was inhibited by increasing the concentration of azaG, then no expulsion took place. Instead, at the end of growth, net incorporation ceased, and a steady-state condition was established in which incorporation equaled breakdown. No azaG degradative enzymes are present in presporulating cells. The possibility is discussed that an increase in the ratio of natural purines to azaG occurred at the time of transition, and that the natural purine derivatives then were reincorporated into RNA preferentially to azaG. The data are consistent with the hypothesis than an increased rate of RNA turnover occurs at the time of transition from vegetative growth to presporulation. Addition of phosphate buffer (pH 7.0, 0.1 m) to azaG-inhibited vegetative cells caused reversal of inhibition, the reversal being accompanied by expulsion of the azaG. At least a partial explanation of this effect is that phosphate causes a decrease in the azaG intracellular pool size.