SummaryCell division in bacteria is governed by a complex cytokinetic machinery in which the key player is a tubulin homologue, FtsZ. Most rod-shaped bacteria divide precisely at mid-cell between segregated sister chromosomes. Selection of the correct site for cell division is thought to be determined by two negative regulatory systems: the nucleoid occlusion system, which prevents division in the vicinity of the chromosomes, and the Min system, which prevents inappropriate division at the cell poles. In Bacillus subtilis recruitment of the division inhibitor MinCD to cell poles depends on DivIVA, and these proteins were thought to be sufficient for Min function. We have now identified a novel component of the division-site selection system, MinJ, which bridges DivIVA and MinD. minJ mutants are impaired in division because MinCD activity is no longer restricted to cell poles. Although MinCD was thought to act specifically on FtsZ assembly, analysis of minJ and divIVA mutants showed that their block in division occurs downstream of FtsZ. The results support a model in which the main function of the Min system lies in allowing only a single round of division per cell cycle, and that MinCD acts at multiple levels to prevent inappropriate division.

The process of endospore formation in Bacillus subtilis is complex, requiring the generation of two distinct cell types, a forespore and larger mother cell. The development of these cell types is controlled and regulated by cell type-specific gene expression, activated by a s-factor cascade. Activation of these cell type-specific sigma factors is coupled with the completion of polar septation. Here, we describe a novel protein, YuaG, a eukaryotic reggie/flotillin homologue that is involved in the early stages of sporulation of the Gram-positive model organism B. subtilis. YuaG localizes in discrete foci in the membrane and is highly dynamic. Purification of detergent-resistant membranes revealed that YuaG is associated with negatively charged phospholipids, e.g. phosphatidylglycerol (PG) or cardiolipin (CL). However, localization of YuaG is not always dependent on PG/CL in vivo. A yuaG disruption strain shows a delay in the onset of sporulation along with reduced sporulation efficiency, where the spores develop to a certain stage and then appear to be trapped at this stage. Our results indicate that YuaG is involved in the early stage of spore development, probably playing a role in the signalling cascade at the onset of sporulation.

Faithful segregation of chromosomes and plasmids is a vital prerequisite to produce viable and genetically identical progeny. Bacteria use a specialized segregation system composed of the partitioning proteins ParA and ParB to segregate certain plasmids. Strikingly, homologues of ParA and ParB are found to be encoded in many chromosomes. Although mutations in the chromosomal Par system have effects on segregation efficiency, the exact mechanism by which the chromosomes are segregated into the daughter cells is not fully understood. We describe the polar localization of the ParB origin nucleoprotein complex in the actinomycete Corynebacterium glutamicum. ParB and the origin of replication were found to be stably localized to the cell poles. After replication, the origins move toward the opposite pole. Purified ParB was able to bind to the parS consensus sequence in vitro. C. glutamicum possesses two ParA-like partitioning ATPase proteins. Both proteins interact with ParB but show a slightly different subcellular localization and phenotype. While ParA might be part of a conventional partitioning system, PldP seems to play a role in division site selection.

SummaryIn eukaryotic and prokaryotic cells the establishment and maintenance of cell polarity is essential for numerous biological processes. In some bacterial species, the chromosome origins have been identified as molecular markers of cell polarity and polar chromosome anchoring factors have been identified, for example in Caulobacter crescentus. Although speculated, polar chromosome tethering factors have not been identified for Actinobacteria, to date. Here, using a minimal synthetic Escherichia coli system, biochemical and in vivo experiments, we provide evidence that Corynebacterium glutamicum cells tether the chromosome origins at the cell poles through direct physical interactions between the ParB-parS chromosomal centromere and the apical growth determinant DivIVA. The interaction between ParB and DivIVA proteins was also shown for other members of the Actinobacteria phylum, including Mycobacterium tuberculosis and Streptomyces coelicolor.

SummaryLipid II flippases play an essential role in cell growth and the maintenance of cell shape in many rod-shaped bacteria. The putative lipid II flippase RodA is an integral membrane protein and member of the SEDS (shape, elongation, division and sporulation) protein family. In contrast to its homologues in Escherichia coli and Bacillus subtilis little is known about the role of RodA in actinobacteria. In this study, we describe the localization and function of RodA in Corynebacterium glutamicum, a rod-shaped, apically growing actinobacterium. RodA-GFP localizes exclusively at the cell poles. Surprisingly, time-lapse microscopy revealed that apical cell growth is sustained in a rodA deletion strain. However, growth rates and antibiotic susceptibility are altered. In the absence of RodA, it appears that apical growth is driven by lateral diffusion of lipid II that is likely flipped by the septal flippase, FtsW. Furthermore, we applied a previously described synthetic in vivo system in combination with FRET to identify an interaction between C. glutamicum RodA and the polar growth organizing protein DivIVA.