Abstract
In many model organisms, diffuse patterning of cell wall peptidoglycan synthesis by the actin homolog MreB enables the bacteria to maintain their characteristic rod shape. In Caulobacter crescentus and Escherichia coli, MreB is also required to sculpt this morphology de novo. Mycobacteria are rod‐shaped but expand their cell wall from discrete polar or subpolar zones. In this genus, the tropomyosin‐like protein DivIVA is required for the maintenance of cell morphology. DivIVA has also been proposed to direct peptidoglycan synthesis to the tips of the mycobacterial cell. The precise nature of this regulation is unclear, as is its role in creating rod shape from scratch. We find that DivIVA localizes nascent cell wall and covalently associated mycomembrane but is dispensable for the assembly process itself. Mycobacterium smegmatis rendered spherical by peptidoglycan digestion or by DivIVA depletion are able to regain rod shape at the population level in the presence of DivIVA. At the single cell level, there is a close spatiotemporal correlation between DivIVA foci, rod extrusion and concentrated cell wall synthesis. Thus, although the precise mechanistic details differ from other organisms, M. smegmatis also establish and propagate rod shape by cytoskeleton‐controlled patterning of peptidoglycan. Our data further support the emerging notion that morphology is a hardwired trait of bacterial cells.
Highlights
Bacteria adopt a variety of characteristic shapes, each with distinct advantages
Using metabolic labeling paired with high resolution microscopy, we find that assembly of peptidoglycan and the mycomembrane occurs but is disorganized upon DivIVA depletion
We noted that spherical mycobacterial cells generated by cell wall digestion [Rastogi and Venkitasubramanian 1979; Yabu and Takahashi 1977; Udou et al 1982; Udou et al 1983], rather than DivIVA depletion, have been reported to reform rods
Summary
Bacteria adopt a variety of characteristic shapes, each with distinct advantages. For example, rod morphology optimizes the surface area to volume ratio and may promote nutrient uptake [Young 2006]. Many well-studied species, including Escherichia coli and Bacillus subtilis, elongate by adding new peptidoglycan along the lateral cell body [de Pedro et al 1997; Daniel and Errington 2003; Wang et al 2012; Scheffers and Pinho 2005; Tiyanont et al 2006; Liang et al 2017] In these organisms, cell shape and spatial regulation of peptidoglycan synthesis are both tied to the actin homolog MreB [van den Ent et al 2001; Gitai et al 2004; Garner et al 2011; van Teeffelen et al 2011; Dominguez-Escobar et al 2011; Errington 2015]. These proteins exhibit structural, not necessarily sequence similarity, to eukaryotic cytoskeleton proteins
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