Saudi Cultural Missions Theses & Dissertations
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Item Restricted Running the Gauntlet of the Bacterial Cell Wall(Newcastle University, 2025) Alofi, Amirah; Daniel, RichardIn nature, bacteria have a variety of shapes, from simple cocci and rods to more complicated spiral or appendage structures. In their life, they need a strong exoskeleton that can maintain their shape during growth and protect them from changes in environmental conditions. This rigid structure is generally provided by the cell wall and is considered an essential component in the bacterial cell. However, the cell wall represents a complex logistical problem in terms of the controlled synthesis and degradation that is required to maintain shape, permit enlargement, and prevent lysis. Significant advances have been made in understanding wall synthesis, and in Gram-negative bacteria synthesis can be integrated with degradation. But, for Gram-positive bacteria the regulation of cell wall degradation is poorly characterised. Genetically the genes encoding the key enzymes are known and the expression of these enzymes are known to be highly regulated. However, understanding how the biochemical activity of these enzymes is restricted and regulated, presumably within the cell wall or on the outside surface of the cell is not clear. The results obtained in this laboratory have indicated that altered cell wall composition or media components modulate the level of the hydrolysis enzyme activity in some way during vegetive growth. This study aimed to extend our understanding of the autolytic systems and how the enzymatic activity may be regulated by components of the cell envelope or minor modifications of the cell wall material.19 0Item Restricted Piptedoglycan Dynamics in Bacillus subtilis(Newcastle University, 2024-09) Aljohani, Alaa; Richard, DanielGram-positive bacterial cell morphology, growth, and division rely on a delicate balance of peptidoglycan synthesis and controlled degradation to maintain the structural integrity of the cell wall. The process of growth involves synthesising new wall material underneath the existing cell wall on the surface of the cell membrane. This growth requires the cell wall degrading enzymes to distinguish between the newly generated wall and the old wall, selectively degrading the outer layers of the wall to facilitate cell enlargement. As the B. subtilis genome encodes 42 genes that are potentially involved in peptidoglycan degradation, systematic deletion of the known autolytic enzymes was used combined with phenotypic analysis for both cell morphological changes and the ability to become motile. From this work, it was found that only 1 of 2 specific autolytic enzymes is functionally required for growth (CwlO and LytE). Although these two autolytic enzymes exhibit a significant degree of functional redundancy, they are required for slightly different aspects of cell morphology. Only CwlO, in concert with CwlQ or CwlS, was also found to be required for the efficient insertion of flagella through the cell wall. Further analysis showed that CwlO activity with respect to cell growth required the activity of a peptidoglycan carboxypeptidase (DacA), but this was not required for flagellar insertion, suggesting that CwlO has two distinct modes of action. In summary, the results of the work presented in this thesis show that the majority of the predicted cell wall degrading enzymes are dispensable, and only 2 enzymes, CwlO and LytE, have critical roles in maintaining normal cell morphology. Interestingly, this study also reveals that the two key autolytic enzymes seem to have distinct modes of action and potentially differ in their substrate specificity. In this respect, a model for cell growth is presented that tries to amalgamate the results of this work with previously published ideas to explain how cell growth is coordinated with respect to peptidoglycan synthesis and degradation without compromising cell integrity and maintaining cell morphology. This model potentially outlines the basic mechanism of cell wall metabolism in Gram-positive rod-shaped bacteria. It also seems that aspects of the mechanism are also conserved in other bacterial species with a different cell morphology as well as in Gram-negative bacteria. These results clearly indicate that the autolytic enzymes and their regulatory mechanisms are potentially interesting novel targets for the development of small molecule antibacterial compounds.30 0