The sigma factors of Bacillus subtilis.

Biofilms are structured communities of cells encased in a polymeric matrix and adherent to a surface, interface or each other. We report here that the soil bacterium Bacillus subtilis forms biofilms. By confocal scanning laser microscopy, we observed that B. subtilis adhered to abiotic surfaces and formed a three-dimensional structure > or =30 microm in depth. These biofilms appeared to be at least partly encased in an extracellular polysaccharide matrix, as they could be stained with Calcofluor, a polysaccharide-binding dye. To understand the molecular mechanism of biofilm formation, we screened previously characterized mutants for a defect in biofilm formation. We found that mutations in spo0A, which encodes the major early sporulation transcription factor, caused a defect in biofilm formation. spo0A mutant cells adhered to a surface in a monolayer of cells rather than a three-dimensional biofilm. The requirement of Spo0A for biofilm development appears to result from its role in negatively regulating AbrB. Mutations in abrB suppressed the biofilm defect of a spo0A mutant, indicating that AbrB negatively regulates at least one gene that is required for the transition from a monolayer of attached cells to a mature biofilm. Implications of biofilm development for the ecology of B. subtilis are discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2958.2001.02709.x

The sporulation transcription factor Spo0A is required for biofilm development in Bacillus subtilis.

Gene expression in members of the family Bacillaceae becomes compartmentalized after the distinctive, asymmetrically located sporulation division. It involves complete compartmentalization of the activities of sporulation-specific sigma factors, sigma(F) in the prespore and then sigma(E) in the mother cell, and then later, following engulfment, sigma(G) in the prespore and then sigma(K) in the mother cell. The coupling of the activation of sigma(F) to septation and sigma(G) to engulfment is clear; the mechanisms are not. The sigma factors provide the bare framework of compartment-specific gene expression. Within each sigma regulon are several temporal classes of genes, and for key regulators, timing is critical. There are also complex intercompartmental regulatory signals. The determinants for sigma(F) regulation are assembled before septation, but activation follows septation. Reversal of the anti-sigma(F) activity of SpoIIAB is critical. Only the origin-proximal 30% of a chromosome is present in the prespore when first formed; it takes approximately 15 min for the rest to be transferred. This transient genetic asymmetry is important for prespore-specific sigma(F) activation. Activation of sigma(E) requires sigma(F) activity and occurs by cleavage of a prosequence. It must occur rapidly to prevent the formation of a second septum. sigma(G) is formed only in the prespore. SpoIIAB can block sigma(G) activity, but SpoIIAB control does not explain why sigma(G) is activated only after engulfment. There is mother cell-specific excision of an insertion element in sigK and sigma(E)-directed transcription of sigK, which encodes pro-sigma(K). Activation requires removal of the prosequence following a sigma(G)-directed signal from the prespore.

https://mmbr.asm.org/content/mmbr/68/2/234.full.pdf

Compartmentalization of Gene Expression during Bacillus subtilis Spore Formation

We describe a general strategy for the identification of genes that are controlled by a specific regulatory factor in vivo and the use of this strategy to identify genes in Bacillus subtilis that are controlled by spo0H, a regulatory gene required for the initiation of sporulation. The general strategy makes use of a cloned regulatory gene fused to an inducible promoter to control expression of the regulatory gene and random gene fusions to a reporter gene to monitor expression in the presence and absence of the regulatory gene product. spo0H encodes a sigma factor of RNA polymerase, sigma H, and is required for the extensive reprograming of gene expression during the transition from growth to stationary phase and during the initiation of sporulation. We identified 18 genes that are controlled by sigma H (csh genes) in vivo by monitoring expression of random gene fusions to lacZ, made by insertion mutagenesis with the transposon Tn917lac, in the presence and absence of sigma H. These genes had lower levels of expression in the absence of sigma H than in the presence of sigma H. Patterns of expression of the csh genes during growth and sporulation in wild-type and spo0H mutant cells indicated that other regulatory factors are probably involved in controlling expression of some of these genes. Three of the csh::Tn917lac insertion mutations caused noticeable phenotypes. One caused a defect in vegetative growth, but only in combination with a spo0H mutation. Two others caused a partial defect in sporulation. One of these also caused a defect in the development of genetic competence. Detailed characterization of some of the csh genes and their regulatory regions should help define the role of spo0H in the regulation of gene expression during the transition from growth to stationary phase and during the initiation of sporulation.

https://jb.asm.org/content/jb/171/8/4121.full.pdf

Identification and characterization of genes controlled by the sporulation-regulatory gene spo0H in Bacillus subtilis.

http://www-stat.wharton.upenn.edu/~stjensen/papers/shanejensen.sige03.pdf

The σE Regulon and the Identification of Additional Sporulation Genes in Bacillus subtilis

Deletion of sigE, the structural gene for the sporulation-induced RNA polymerase sigma factor, sigma E, prevented endospore formation by Bacillus subtilis. The effects of integration of plasmids into the sigE region of the chromosome and the use of complementation analyses demonstrated that sigE is part of an operon that includes a promoter-proximal gene, spoIIGA, that is essential for sporulation. Gene fusions to the promoter of this operon, spoIIG, demonstrated that transcription from this promoter is induced at the beginning of sporulation and is dependent on several spoO genes.

Organization and regulation of an operon that encodes a sporulation-essential sigma factor in Bacillus subtilis.

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Organization and regulation of an operon that encodes a sporulation-essential sigma factor in Bacillus subtilis.