| The interaction of bacteria with their environment plays an important role in controlling bacterial physiology and behavior. Bacteria often respond to their environment in ways that are detrimental to human health and industry, such as when biofilms form on implanted medical devices or on filters used for water purification. These interactions are also interesting from a basic science perspective, and raise the following questions: (1) how do bacteria sense their environment?; (2) what properties of the environment are sensed by bacteria?; and (3) what are the genetic and biochemical changes that bacteria make in response to different properties of their environments? The research described in this thesis addresses these questions from several different perspectives. First, the development and validation of a method for measuring cell wall stiffness are described. Due to its role in bacteria-environment interactions—both directly and as a scaffold for outer membrane proteins that respond to specific environmental signals—the physical properties of the cell wall are a vital piece of information in understanding the response of cells to their environment. We discovered that several different types of bacteria have similar cell wall mechanical properties, and that the bacterial cytoskeletal protein MreB does not affect longitudinal cell stiffness in Escherichia coli. Second, the characterization and application of polyacrylamide (PA) as a substrate for bacterial cell culture is described. The chemical and physical properties of PA hydrogels can be carefully controlled, making them ideal for studies of bacteria-surface interactions. We found that the chemistry of the hydrogel has a significant impact on the growth rate of E. coli, but polymer stiffness does not. Finally, the morphological changes that occur upon surface sensing by Proteus mirabilis are described, and the consequences of those changes in environments that may more closely mimic the bacterium's natural environment are examined. We discovered that cells with a greater surface density of flagella are able to move more rapidly through viscous environments independently of cell length. Together, these studies cast new light on mechanisms and underlying principles that control bacteria-environment interactions. |
