ESSENTIAL PATHWAYS AND GENE REGULATION FOR CELL WALL HOMEOSTASIS IN BACILLUS SUBTILIS
The cell wall is an essential component of most bacterial cells, and cell wall targeting antibiotics have greatly improved human health and life span. Despite intense research over the last 50 years, we still lack a complete understanding of how bacteria maintain cell wall homeostasis. Here we attempt to integrate new data from the last few years with some established ideas in the field, and we propose a new model of cell wall biogenesis in rod-shaped bacteria (Chapter 1). The lipid II cycle is central to peptidoglycan (PG) synthesis. A common C55 lipid carrier, undecaprenyl-pyrophosphate (UPP) is used for the synthesis of both peptidoglycan and wall teichoic acids to ferry precursors across the cytoplasmic membrane. Here we demonstrate that B. subtilis requires either one of two UPP phosphatases, UppP or BcrC, for the recycling of this essential molecule for continuous synthesis of cell wall (Chapter 2). Peptidoglycan synthesis relies on intermediates derived from central metabolism. We found that an aspB mutant is auxotrophic for aspartate and lyses when grown on Difco sporulation medium due to limitation of the peptidoglycan precursor meso-2,6-diaminopimelate (mDAP), a downstream metabolic intermediate of aspartate. Interestingly, we found that when bacteria experience a shortage of aspartate, the first breakpoint is not protein but peptidoglycan synthesis, which predisposes them to cell wall weakness and sensitizes them to antibiotics targeting late steps of PG synthesis. This work highlights the ability of perturbations of central metabolism to sensitize cells to peptidoglycan synthesis inhibitors (Chapter 3). Bacillus subtilis uses alternative sigma factors to regulate gene transcription upon stresses. Being a powerful double-edged sword, it is essential to keep this regulatory network under check. Here we show that the absence of its anti-sigma factor(s) leads to dysregulation of SigM, which drives a positive feedback loop for its own synthesis and SigM accumulates to a toxic level. High SigM activity overproduces membrane proteins and causes protein secretion stress, which lead to cell morphology and severe growth defects (Chapter 4). Collectively, the work in this dissertation provides additional insights of essential pathways and gene regulation for cell wall homeostasis in Bacillus subtilis.
Regulation; Microbiology; Bacillus subtilis; Bacteria; Cell Wall; Peptidoglycan; synthesis
Helmann, John D.
Feigenson, Gerald W.; Angert, Esther R.
Ph. D., Microbiology
Doctor of Philosophy
Attribution-NoDerivatives 4.0 International
dissertation or thesis
Except where otherwise noted, this item's license is described as Attribution-NoDerivatives 4.0 International