FtsA Mutants ofBacillus subtilisImpaired in Sporulation

Abstract

Spore formation in Bacillus subtilis involves a switch in the site of cell division from the midcell to a polar position. Both medial division and polar division are mediated in part by the actin-like, cytokinetic protein FtsA. We report the isolation of an FtsA mutant (FtsA D265G ) that is defective in sporulation but is apparently unimpaired in vegetative growth. Sporulating cells of the mutant reach the stage of asymmetric division but are partially blocked in the subsequent morphological process of engulfment. As judged by fluorescence microscopy and electron microscopy, the FtsA D265G mutant produces normal-looking medial septa but immature (abnormally thin) polar septa. The mutant was unimpaired in transcription under the control of Spo0A, the master regulator for entry into sporulation, but was defective in transcription under the control of F , a regulatory protein whose activation is known to depend on polar division. An amino acid substitution at a residue (Y264) adjacent to D265 also caused a defect in sporulation. D265 and Y264 are conserved among endospore-forming bacteria, raising the possibility that these residues are involved in a sporulation-specific protein interaction that facilitates maturation of the sporulation septum and the activation of F .Most bacteria divide by binary fission, forming a septum at the midpoint of the long axis of the cell to produce identicalsized progeny. The gram-positive soil bacterium Bacillus subtilis exhibits an additional mode of division when it enters the pathway to sporulate. Under such conditions, it undergoes a process of asymmetric division in which a septum is formed at a polar rather than a medial position. The polar septum divides the cell asymmetrically into a forespore (the smaller cell) and a mother cell. The forespore and the mother cell each receive a chromosome but exhibit dissimilar programs of gene expression (reviewed in reference 37). Gene expression in the forespore is governed by the transcription factor F , whose activation depends on the formation of the polar septum, whereas gene expression in the mother cell depends on the transcription factor E . Following asymmetric division, the forespore is engulfed by the mother cell in a phagocyte-like process that results in the forespore becoming pinched off as a free protoplast within the mother cell.The switch from medial division during growth to asymmetric division during sporulation involves a change in the subcellular localization of the cytokinetic protein FtsZ. This tubulinlike GTPase assembles into a ring-like structure, called the Z-ring, at the future site of septation (7, 49). During vegetative growth, the Z-ring assembles at the middle of the cell, fixing the position of the division site. The Z-ring is disassembled during cytokinesis and is largely absent from the completed septum. During sporulation, the Z-ring switches to a bipolar pattern of localization, forming a ring near each pole of the cell (29). Recent evidence indicates that the switch from medial to bipolar Z-rings occur...

Inactivation of σ E and σ G in Clostridium acetobutylicum Illuminates Their Roles in Clostridial-Cell-Form Biogenesis, Granulose Synthesis, Solventogenesis, and Spore Morphogenesis

“…In contrast, the B. subtilis sigE disruption mutant formed a proper asymmetric septum (14). However, the B. subtilis ftsA inactivation mutant rendered a phenotype that was blocked at asymmetric septum formation (18), which is similar to EKO1. FtsA is an actin-like protein that acts in concert with the cytokinetic protein FtsZ to direct septum formation (18).…”

Requirement for the Cell Division Protein DivIB in Polar Cell Division and Engulfment during Sporulation inBacillus subtilis

“…We proposed that the more stringent requirement for divIB in sporulation at low temperatures may be due to a modified role for divIB in asymmetric division during sporulation. A dedicated role for the cell division protein FtsA of B. subtilis in sporulationspecific septation has been suggested previously (28). Alternatively, DivIB may have a role in sporulation separate from asymmetric division.…”

DNA Array-Based Transcriptional Analysis of Asporogenous, Nonsolventogenic Clostridium acetobutylicum Strains SKO1 and M5

“…A notable gene of cluster S2 is ftsZ (CAC1693), which is part of a predicted bicistronic operon (CAC1692 and CAC1693). The cell division GTPase FtsZ and its partner FtsA play an essential role in cell division and sporulation in B. subtilis and all eubacteria (7,13). Of the genes in cluster S2, 72% belong to transcriptional units (operons) with promoter regions predicted to have a 0A box, while 44% have a predicted F binding site.…”