Compartmentalization of Gene Expression duringBacillus subtilisSpore Formation

Abstract

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

Repeated triggering of sporulation in Bacillus subtilis selects against a protein that affects the timing of cell division

“…During batch fermentations, to which 1 mM glucose is sequentially applied, pH and pO 2 both drop upon glucose influx ( The processes of sporulation initiation, spore maturation and germination take a minimum of B9 h: 7 h to form a spore (Hilbert and Piggot, 2004) and 1.5-2 h for 490% of the spores to germinate under the conditions used in this study (Supplementary Information SI6;Supplementary Figures S5 and S6). As the full-length experiment lasts for 20 h, such cycles can occur, causing the mixing of generations.…”

“…Initiation of sporulation to spore maturation lasts B7 h (Hilbert and Piggot, 2004); thus, sporulation is initiated in part of the population before glucose is depleted. From these data we assume that 1 mM of glucose is consumed within B1 h (albeit dependent on biomass and portion of metabolically active cells) and that sporulation is by then induced in part of the population (Dixon and Spiegelman, 2002).…”

Genome-wide analysis of temporally regulated and compartment-specific gene expression in sporulating cells of Bacillus subtilis

“…Each cell type receives a copy of the bacterial chromosome, and deploys specific but interdependent genetic programmes controlled by the successive appearance of the s F , s E , s G and s K subunits of RNA polymerase (reviewed by Errington, 2003;Hilbert & Piggot, 2004;Stragier & Losick, 1996). Entry into sporulation is induced by nutrient starvation, and is mainly controlled through phosphorylation of the Spo0A response regulator (Burbulys et al, 1991;Phillips & Strauch, 2002;Sonenshein, 2000).…”

The histidine kinase inhibitor Sda binds near the site of autophosphorylation and may sterically hinder autophosphorylation and phosphotransfer to Spo0F

“…Because kinA is subject to complex transcriptional regulation and indirectly regulates its own expression by positive and negative feedback loops (Hilbert and Piggot, 2004), we screened for kinA mutations using a strain of B. subtilis in which the sole copy of kinA was expressed from a constitutive promoter integrated at an ectopic site in the chromosome (DkinA::kan lacA::P veg-kinA). In this strain, sda was expressed from an IPTG-inducible promoter integrated at a second ectopic site in the chromosome (amyE::Pspac(hy)-sda; strain KC49).…”

“…Following autophosphorylation, KinA and KinB transfer phosphate to their cognate response regulator, Spo0A, through two phosphotransfer proteins, Spo0F and Spo0B (Burbulys et al, 1991). Spo0A is a transcription factor that, when phosphorylated to high levels by KinA and KinB, activates transcription of the genes that initiate spore development (Hilbert and Piggot, 2004).…”