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Mechanisms for maintaining cell shape in rod-shaped Gram-negative bacteria.
Mol Microbiol. 2011 Jul; 81(2):340-53
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14 Jul 2011
New Finding, Technical Advance
DOI: 10.3410/f.11890956.13000054
If you thought at school, like I did, that mechanics is boring, this paper might change your mind.
Furchtgott et al. developed a mechanical model of growing peptidoglycan where the disaccharide units are represented as stiff springs and the peptide cross-links are represented as flexible springs, and...Continue reading
Furchtgott et al. developed a mechanical model of growing peptidoglycan where the disaccharide units are represented as stiff springs and the peptide cross-links are represented as flexible springs, and...Continue reading
If you thought at school, like I did, that mechanics is boring, this paper might change your mind.
Furchtgott et al. developed a mechanical model of growing peptidoglycan where the disaccharide units are represented as stiff springs and the peptide cross-links are represented as flexible springs, and the turgor pressure pushes this spring network into its force equilibrium shape. The authors show that random insertion of new strands leads to a positive feedback, as areas of higher density of peptidoglycan are more likely to have a new strand inserted leading to bulges etc., so this mechanism does not work. Their experiments show that a rod-shaped Gram-negative cell maintains its width (different species have different widths) during elongation and that the rod remains straight, key features the model has to match. Replacing random insertion with insertion along a helical structure (as given by the MreB cytoskeleton) uncouples insertion site selection from insertion site density and allows the cell to maintain width and grow straight. Tension-dependent insertion does not work. Cell width increases with the length of the new strands being inserted and how much they are stretched during insertion.
Furchtgott et al. developed a mechanical model of growing peptidoglycan where the disaccharide units are represented as stiff springs and the peptide cross-links are represented as flexible springs, and the turgor pressure pushes this spring network into its force equilibrium shape. The authors show that random insertion of new strands leads to a positive feedback, as areas of higher density of peptidoglycan are more likely to have a new strand inserted leading to bulges etc., so this mechanism does not work. Their experiments show that a rod-shaped Gram-negative cell maintains its width (different species have different widths) during elongation and that the rod remains straight, key features the model has to match. Replacing random insertion with insertion along a helical structure (as given by the MreB cytoskeleton) uncouples insertion site selection from insertion site density and allows the cell to maintain width and grow straight. Tension-dependent insertion does not work. Cell width increases with the length of the new strands being inserted and how much they are stretched during insertion.
Disclosures
None declared
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Kreft J: F1000Prime Recommendation of [Furchtgott L et al., Mol Microbiol 2011, 81(2):340-53]. In F1000Prime, 14 Jul 2011; DOI: 10.3410/f.11890956.13000054. F1000Prime.com/11890956#eval13000054
F1000Prime Recommendations, Dissents and Comments for [Furchtgott L et al., Mol Microbiol 2011, 81(2):340-53]. In F1000Prime, 22 May 2013; F1000Prime.com/11890956
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For the rod-shaped Gram-negative bacterium Escherichia coli, changes in cell shape have critical consequences for motility, immune system evasion, proliferation and adhesion. For most bacteria, the peptidoglycan cell wall is both necessary and sufficient to determine cell shape. However, how the synthesis machinery assembles a peptidoglycan network with a robustly maintained micron-scale shape has remained elusive. To explore shape maintenance, we have quantified the robustness of cell shape in three Gram-negative bacteria in different genetic backgrounds and in the presence of an antibiotic that inhibits division. Building on previous modelling suggesting a prominent role for mechanical forces in shape regulation, we introduce a biophysical model for the growth dynamics of rod-shaped cells to investigate the roles of spatial regulation of peptidoglycan synthesis, glycan-strand biochemistry and mechanical stretching during insertion. Our studies reveal that rod-shape maintenance requires insertion to be insensitive to fluctuations in cell-wall density and stress, and even a simple helical pattern of insertion is sufficient for over sixfold elongation without significant loss in shape. In addition, we demonstrate that both the length and pre-stretching of newly inserted strands regulate cell width. In sum, we show that simple physical rules can allow bacteria to achieve robust, shape-preserving cell-wall growth.
© 2011 Blackwell Publishing Ltd.
DOI: 10.1111/j.1365-2958.2011.07616.x
PMID: 21501250
