Cell morphogenesis in Bacillus subtilis: from genetics to exploitation

Bacteria are the most abundant and diverse organisms on the planet. They occupy every conceivable niche in the environment and they are incredibly diverse in the ways they can survive and thrive in even the most difficult places. They are major players in most of the key cycles that keep our planet clean and fresh. They inhabit our bodies and the friendly bacteria in our guts help us digest food and protect us from disease. Bacteria are also some of the most deadly disease-causing agents. For all of these reasons, we need to understand the fundamental properties of bacteria. Bacterial cells differ from our own in possessing a tough outer shell called the wall. This critical structure protects the cells from damage and prevents the cell contents from bursting due to the high inside pressure they like to maintain. TA particularly interesting feature of the wall is that it needs to be enlarged to accommodate cell growth, whilst at all times remaining intact. Because the cell wall is critical and there is no equivalent structure in human cells, the wall is also the target for the best of our antibiotics. Despite its importance, our understanding of the wall and how it is made remain rather poor. The object of this project is to study the properties of the wall in a well characterized bacterium, Bacillus subtilis, which is very amenable to experimentation. We wish to identify all of the factors that are needed to make a wall and study how they work, from the whole cell, right down to the molecular level. The knowledge that emerges will have important implications for our understanding of wall synthesis in all bacteria, and it may help us to find new antibiotics that will help to keep disease agents at bay.

All major branches of the bacterial sub-kingdom possess a cell wall containing peptidoglycan (PG), which is a huge mesh-like network that covers the whole surface of the cell. PG consists of long glycan strands cross linked by peptide bridges. The precursors for PG are made inside the cell and then polymerized on the outside by the action of penicillin-binding proteins (PBPs). Autolytic enzymes cleave bonds in the PG in a controlled manner to allow orderly growth of the cell. The walls of Gram positive bacteria contain an almost equal mass of one or more anionic polymers called teichoic acids, the functions of which remain poorly understood. The cell wall is a crucial structure for bacteria because it opposes the cytoplasmic turgor pressure on the cytoplasmic membrane, preventing the cell from bursting, as well as providing protection from mechanical damage. The wall is also the target for the best of our antibiotics, particularly ?-lactams and glycopeptides. Despite many decades of research, many features of cell wall biogenesis remain poorly understood. The aim of this project is to identify most, if not all of the genes and proteins required for cell wall biogenesis in the experimentally tractable model Gram positive bacterium Bacillus subtilis. Then to systematically characterize the components of the synthetic machinery in terms of mutant phenotype, gene-gene and protein-protein interactions and protein localization. Selected elements of the systems will be characterized in terms of biochemical function and protein structure. New knowledge emerging from the programme will be used to design screens for small molecule inhibitors that could provide inhibitors for use as experimental reagents or antibiotic leads.