Bacteria in the environment face constant stress, due to lack of nutrients or presence of growth inhibiting compounds. As a result, they have developed several strategies to evade unfavourable growth conditions. These range from entering into dormant or quiescent states, through to motility, and biofilm formation. Using the model organism Streptomyces, we investigated how the bacterial cell surface regulates dormancy, biofilm formation, and motility.
Dormancy via spore formation allows cells to shut down metabolism in response to poor nutrient conditions. Spores can then be dispersed throughout the environment to encounter favourable conditions. This is an incredibly resilient survival strategy, so long as the spores resuscitate from dormancy and resume growth once favourable conditions are sensed. We established that peptidoglycan remodeling by resuscitation promoting factors is critical for rapid germination of dormant Streptomyces spores, which likely provides a competitive advantage over slower growing microbes in the same environment. Previously it was thought that these proteins produce a signal to stimulate germination in neighbouring cells. We determined that the resuscitation promoting factors are lytic transglycosylases, and were not capable of producing a germination signal on their own. Instead, they function by cleaving the peptidoglycan to make room for new cell growth. This work highlights the importance of peptidoglycan remodeling to the germination process. Biofilms are multicellular communities of microorganisms which are adhered to each other using a protective matrix. Formation of biofilms is thought to be inversely correlated with motility. We established that Streptomyces forms biofilms during the exploratory growth identifying potential extracellular matrix components. These biofilms use sliding motility to expand rapidly across their environment. Components of the biofilm matrix effect colony expansion, suggesting that biofilm formation and motility are intricately linked in Streptomyces. These works demonstrate the importance of surface polymers to the growth and development of Streptomyces. / Thesis / Doctor of Philosophy (PhD) / Bacteria are all around us. In these different environments, whether in the soil, or inside our guts, or in a body of water, they will encounter stress. This can take the shape of nutrient stress, or the presence of growth inhibiting compounds. In response, bacteria can evade these poor conditions by entering into dormancy, analogous to hibernation, by building a biofilm, analogous to building a bunker, or by moving away. The surface of bacterial cells becomes decorated with different polymers as it transitions into one of these three modes of stress evasion. The cell wall holds the cell together and supports its shape, making it the most important surface polymer. I examined how rapid remodeling of the cell wall provides a competitive advantage to cells waking up from dormancy. I also examined the importance of additional polymers to the formation of biofilms that slide across surfaces, away from stressors. These works establish how important the surface of the bacterium is for surviving stressful conditions.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/24141 |
| Date | January 2018 |
| Creators | Sexton, Danielle |
| Contributors | Elliot, Marie, Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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