The regulation of competence transcription factor synthesis constitutes a critical control point in the regulation of competence in Bacillus subtilis

Abstract

comK, which encodes the competence transcription factor, is itself transcriptionally activated at the transition from exponential growth to stationary phase in Bacillus subtilis. MecA, a negative regulator of competence, also inhibits comK transcription when overexpressed, and a mec4 null mutation results in comK overexpression. Although null mutations in mecA, as well as in another gene, mecB, are known to bypass the requirements for nearly all of the competence regulatory genes, the comK requirement is not suppressed by mecA inactivation. Various competence reulatory genes (comA srfA, degU, abrB, sin, and spoOA) are shown to be required for the expression of comK srfA transcription is shown to occur equally in cells destined for competence and those destined not to become competent. In contrast, comK transcription is restricted to the presumptive competent cells. These and other results are combined to describe a regulatory pathway for competence.

A new Bacillus subtilis gene, med, encodes a positive regulator of comK

“…We next examined the effect of the med mutation on sporulation, since Spo0A and AbrB constitute a regulatory branch different from those involving the above-mentioned three factors (11,12,48). As shown in Table 4, the mutation did not affect sporulation efficiency, showing that Med does not affect the Spo0A function (see also Discussion).…”

“…We have shown previously that a null mutation of mecA markedly reduces ␤-galactosidase activity driven by degRЈ-ЈlacZ and that this reduction is due to repression of degR by the competence transcription factor ComK overproduced by the mecA mutation (32). The expression of comK is subject to regulation by diverse regulatory factors including ComS, Spo0A, DegU, SinR, AbrB, and ComK itself (10,12,21,48). We therefore expected that we could isolate in this experimental system a novel mutant(s) in which the expression of comK was reduced.…”

“…DegS, a sensor kinase, is thought to respond to environmental or internal stimuli, autophosphorylate, and then transfer the phosphate to DegU (3,27). Phosphorylated DegU stimulates the production of extracellular proteases and levansucrase, while unphosphorylated DegU is required for transcription of comK and thus participates in competence development (3,12,48). The production of the exoproteases is also subject to additional positive and negative regulation by several factors (20,26).…”

“…Another positive regulator of competence development, SinR, may be required for optimal comS expression (10,21). In addition, the Spo0A-AbrB system acts on comK regulation independently of the route involving MecA and ClpC, and CodY is also required for nutritional repression of comK (11,12,41,48). The importance of all of this regulation of comK is that ComK is the direct positive regulator of transcription of the late competence genes that encode the apparatus for processing and incorporating exogenous DNA into the cell (12,48,50,51).…”

“…In addition, the Spo0A-AbrB system acts on comK regulation independently of the route involving MecA and ClpC, and CodY is also required for nutritional repression of comK (11,12,41,48). The importance of all of this regulation of comK is that ComK is the direct positive regulator of transcription of the late competence genes that encode the apparatus for processing and incorporating exogenous DNA into the cell (12,48,50,51). ComK also activates genes such as sacB, nucA, and recA which are not related to competence development (14,25,49).…”