Dual-specificity anti-sigma factor reinforces control of cell-type specific gene expression in Bacillus subtilis

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Development

Background:

• Gene expression during Bacillus subtilis spore development is orchestrated by cell type-specific RNA polymerase sigma factors.
• Sigma factors like σF and σE control early development in forespores and mother cells, respectively, with transitions to σG and σK post-engulfment.
• The anti-sigma factor CsfB, initially controlled by σF, inhibits σG and influences early to late gene expression switches.

Purpose of the Study:

• To investigate the role of CsfB in mother cell gene expression after engulfment.
• To determine the mechanism by which CsfB discriminates between different sigma factors.
• To elucidate how CsfB establishes negative feedback loops to regulate sigma factor activity and developmental timing.

Main Methods:

• Analysis of csfB gene expression under the control of σK in the mother cell.
• Biochemical assays to assess CsfB binding and inhibition of σE and σK.
• Site-directed mutagenesis to identify key residues in sigma factors responsible for CsfB discrimination.

Main Results:

• CsfB is expressed in the mother cell post-engulfment under σK control.
• CsfB inhibits σE but not σK, with discrimination mediated by a residue in region 2.3.
• CsfB prevents premature activation of σG in the mother cell and σK activation dependent on σG.

Conclusions:

• CsfB establishes negative feedback loops, curtailing σE activity and preventing ectopic σG activation in the mother cell.
• CsfB's ability to differentiate between highly similar sigma factor pairs (σF/σG and σE/σK) reinforces cell-type specificity.
• CsfB plays a crucial role in regulating the transition from early to late development in Bacillus subtilis spore formation.