Morphogenesis of rod-shaped sacculi

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Elongation of many rod-shaped bacteria occurs by peptidoglycan synthesis at discrete foci along the sidewall of the cells. However, within the Rhizobiales, there are many budding bacteria, in which new cell growth is constrained to a specific region. The phylogeny of the Rhizobiales indicates that this mode of zonal growth may be ancestral. We demonstrate that the rod-shaped bacterium Agrobacterium tumefaciens grows unidirectionally from the new pole generated after cell division and has an atypical peptidoglycan composition. Polar growth occurs under all conditions tested, including when cells are attached to a plant root and under conditions that induce virulence. Finally, we show that polar growth also occurs in the closely related bacteria Sinorhizobium meliloti , Brucella abortus , and Ochrobactrum anthropi . We find that unipolar growth is an ancestral and conserved trait among the Rhizobiales, which includes important mutualists and pathogens of plants and animals.

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confidence: 99%

Polar growth in the Alphaproteobacterial order Rhizobiales

Brown

Pedro

Kysela

et al. 2012

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“…There were no abnormal morphologies at the growth poles in Cb-treated cells, suggesting unipolar growth uses Cb-insensitive PG synthesis enzymes. M uch of our understanding of the growth and division of rodshaped bacterial cells is based on investigations of distinct elongase and divisome protein complexes in the γ-proteobacterium Escherichia coli (1). The elongase adds peptidoglycan (PG) at discrete equally spaced sites along the cylindrical cell between the poles.…”

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confidence: 99%

Dynamic FtsA and FtsZ localization and outer membrane alterations during polar growth and cell division in Agrobacterium tumefaciens

Zupan

Cameron

Anderson-Furgeson

et al. 2013

Growth and cell division in rod-shaped bacteria have been primarily studied in species that grow predominantly by peptidoglycan (PG) synthesis along the length of the cell. Rhizobiales species, however, predominantly grow by PG synthesis at a single pole. Here we characterize the dynamic localization of several Agrobacterium tumefaciens components during the cell cycle. First, the lipophilic dye FM 4-64 predominantly stains the outer membranes of old poles versus growing poles. In cells about to divide, however, both poles are equally labeled with FM 4-64, but the constriction site is not. Second, the cell-division protein FtsA alternates from unipolar foci in the shortest cells to unipolar and midcell localization in cells of intermediate length, to strictly midcell localization in the longest cells undergoing septation. Third, the cell division protein FtsZ localizes in a cell-cycle pattern similar to, but more complex than, FtsA. Finally, because PG synthesis is spatially and temporally regulated during the cell cycle, we treated cells with sublethal concentrations of carbenicillin (Cb) to assess the role of penicillin-binding proteins in growth and cell division. Cb-treated cells formed midcell circumferential bulges, suggesting that interrupted PG synthesis destabilizes the septum. Midcell bulges contained bands or foci of FtsA-GFP and FtsZ-GFP and no FM 4-64 label, as in untreated cells. There were no abnormal morphologies at the growth poles in Cb-treated cells, suggesting unipolar growth uses Cb-insensitive PG synthesis enzymes.agrobacterium cell cycle | bacterial cell growth | bacterial cell division | peptidoglycan synthesis

“…The prevalent view proposes that cytoskeletal filaments such as tubulin-like FtsZ and actin-like MreB spatially regulate PG insertion (13)(14)(15). Experimental evidence suggests that the cell wall exhibits partial order with glycan strands roughly oriented perpendicular (possibly with some tilt) to the long axis of a rod-shaped cell (16)(17)(18).…”

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confidence: 99%

Processivity of peptidoglycan synthesis provides a built-in mechanism for the robustness of straight-rod cell morphology

Sliusarenko

Cabeen

Wolgemuth

et al. 2010

The propagation of cell shape across generations is remarkably robust in most bacteria. Even when deformations are acquired, growing cells progressively recover their original shape once the deforming factors are eliminated. For instance, straight-rod-shaped bacteria grow curved when confined to circular microchambers, but straighten in a growth-dependent fashion when released. Bacterial cell shape is maintained by the peptidoglycan (PG) cell wall, a giant macromolecule of glycan strands that are synthesized by processive enzymes and cross-linked by peptide chains. Changes in cell geometry require modifying the PG and therefore depend directly on the molecular-scale properties of PG structure and synthesis. Using a mathematical model we quantify the straightening of curved Caulobacter crescentus cells after disruption of the cell-curving crescentin structure. We observe that cells straighten at a rate that is about half (57%) the cell growth rate. Next we show that in the absence of other effects there exists a mathematical relationship between the rate of cell straightening and the processivity of PG synthesis-the number of subunits incorporated before termination of synthesis. From the measured rate of cell straightening this relationship predicts processivity values that are in good agreement with our estimates from published data. Finally, we consider the possible role of three other mechanisms in cell straightening. We conclude that regardless of the involvement of other factors, intrinsic properties of PG processivity provide a robust mechanism for cell straightening that is hardwired to the cell wall synthesis machinery.cell shape | cell wall | cell curvature | modeling B acteria exhibit a wide variety of shapes, which are precisely maintained over countless generations in most species, though the mechanisms of the process are not well understood. Many bacteria display rod shape, which can confer selective advantages (1). In nature bacteria frequently grow in dense environments such as soil and colonies, and are therefore likely to experience physical constraints. For example, chemotactic rodshaped bacteria are capable of penetrating channels narrower than their diameter to reach nutrient sources. Within the channels, growing and dividing cells undergo significant mechanical stress and acquire various deformed cell shapes (2). Similarly, recent experiments using microchambers showed that external physical forces can cause straight-rod-shaped cells to grow curved (3,4). Once the force is released, cells gradually return to their native straight-rod shape as growth continues (2-4). The properties of cell shape recovery have not received much attention, yet they have important implications for the robust maintenance of cell shape throughout bacterial populations.Here we focus on the straightening of curved rod-shaped cells. Using a mathematical model we show first that straightening of exponentially growing cells is a rather surprising phenomenon that would not occur without a specific mechanism. We then dis...