Expression of competence genes in Bacillus subtilis.
A set of competence (com) mutants of Bacillus subtilis was constructed by using Tn917lacZ as a mutagen. In about half of the mutants, the promoterless lacZ element on the transposon was placed under control of putative com promoters. Expression of the mutant com genes was studied by using the beta-galactosidase tag. Two of the mutant genes (those represented by com-124 and com-138) were expressed early in the growth cycle in all of the media tested and were not dependent on the spo0A or spo0H product for expression. The remaining mutants, which represented a minimum of four additional genes, expressed beta-galactosidase in stationary phase during the period in which competence developed. We conclude that expression of com genes is probably regulated transcriptionally and in a growth stage-specific manner. Expression of these genes was also dependent on growth in competence medium and, like competence development, required the presence of glucose and was dependent on the spo0H products. The dependence on the spo0A gene product was partially bypassed by the abrB703 mutation. These effects were qualitatively equivalent to those on competence development. The latter was dependent on spo0A and spo0H, and the spo0A dependency was partially suppressed by abrB703. Several of the mutants were still capable of resolution into light and heavy buoyant density cell fractions when grown in competence medium. All of these expressed beta-galactosidase to a greater extent in the light fraction, showing that expression of these com genes was cell type specific. Development of competence was not markedly affected by mutations in spo0B, spo0E, spo0F, spo0J, or sigB, the structural gene of sigma 37.