Importance of being cross-linked for the bacterial cell wall

Abstract

The bacterial cell wall is primarily composed of a mesh of stiff glycan strands cross-linked by peptide bridges and is essential for safeguarding the cell. The structure of the cell wall has to be stiff enough to bear the high turgor pressure and sufficiently tough to ensure protection against failure.Here we explore the role of various design features of the cell in enhancing the toughness of the cell wall. We explain how the glycan strand length distribution and the degree of cross-linking can play a vital role in ensuring that the cell wall offers sufficient resistance to propagation of cracks. We suggest a possible mechanism by which peptide bond hydrolysis can also help mitigate this risk of failure. We also study the reinforcing effect of MreB on the cell wall and conclude that the cross-linked structure of the cell wall plays the more important role in safeguarding against mechanical failure due to cracking..

Modeling heterogeneities in the crosslinked bacterial sacculus

“…As explained in Appendix, it is always true that x i x m x f , it is interesting to observe from Eqs. (16) and (17) that as the variability in k and f is limited with f 1 ≈ f 2 and k 1 ≈ k 2 , we have that x i ≈ x m ≈ x f in this case, which highlights the decidedly brittle response to loading of the system in this case, with the spring breaking being initiated, the system attaining its load maximum and system failure all occurring when virtually the same shear displacement has been applied to it. As the parameters f 1 and k 1 change, the displacement x m shows rather intriguing crossover behavior: when f 1 /k 1 1, x m exhibits independence from the value of f 1 but as f 1 approaches k 1 and becomes greater than it, this behavior crossover to one where there is a dependence of x m on f 1 .…”

“…Nonetheless, the relevance of these features of disorder on the mechanical properties of the cell wall has not been well studied, even as it can shed light on a number of experimental observations of the cell wall. For instance, in a previous work [16], we had explored the mechanical effect of length distribution of the glycan strands and had shown how terminally crosslinked smaller length glycan strands can enhance the toughness of the cell wall, giving an explanation of experimental observations of the presence of shorter length glycan strands and the preference for crosslinking to happen at the ends of the glycan strands [11,14].…”