Studies of σ(D)-dependent functions in bacillus subtilis

Gene expression in Bacillus subtilis can be controlled by alternative forms of RNA polymerase programmed by distinct σ factors. One such factor, σ(D) (σ²⁸), is expressed during vegetative growth and has been implicated in the transcription of a regulon of genes expressed during exponential growth and the early stationary phase. We have studies several functions related to flagellar synthesis and chemotaxis in B. subtilis strains in which σ(D) is missing or is present at reduced levels. Previous studies showed that a null mutant, which contains a disrupted copy of the σ(D) structural gene (sigD), fails to synthesize flagellin and grows as long filaments. We now show that these defects are accompanied by the lack of synthesis of the methyl-accepting chemotaxis proteins and a substantial decrease in two autolysin activities implicated in cell separation. A strain containing an insertion upstream of the sigD gene that reduces the level of σ(D) protein grew as short chains and was flagellated but was impaired in chemotaxis and/or motility. This reduced level of σ(D) expression suggests that the sigD gene may be part of an operon. A strain containing an insertion downstream of the sigD gene expressed nearly wild-type levels of σ(D) protein but was also impaired in chemotaxis and/or motility, suggesting that genes downstream of sigD may also be involved in these functions. Genetic experiments demonstrate that sigD is allelic to the flaB locus, which was initially isolated as a locus affecting flagellin expression (G.F. Grant and M.I. Simon, J. Bacteriol. 99:116-124, 1969).