Partial Purine Deprivation Causes Sporulation of Bacillus subtilis in the Presence of Excess Ammonia, Glucose and Phosphate

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Abstract
In strains of B. subtilis able to synthesize purines de novo, massive sporulation is suppressed by the combination of excess NH3, glucose and phosphate. Purine auxotrophs, blocked in the general or the guanine-specific portion of the branched purine pathway, sporulated in such a medium when the purine required for normal growth was removed from the medium. The resulting spore titer and the sporulation frequency increased with the residual growth rate in the purine-free medium, i.e., with the leakiness of the purine mutation. Sporulation was further increased by allowing residual growth in growth-limiting amounts of guanosine. Non-leaky purine mutants blocked before 5''-phosphoribosyl-5-amino-4-imidazole carboxamide also sporulated well when supplied with 5-amino-4-imidazole carboxamide at concentrations (2 mM) that supported growth at a suboptimal rate.