| Biofilms are increasingly recognized as the predominant state for most bacteria. Persistence and survival under various environmental stresses has been attributed to the capacity to form biofilms, which are also crucial for successful colonization of hosts. In the present dissertation, biofilms formed by the mutualistic bacterium Vibrio fischeri were studied in an effort to describe the molecular basis of community formation, and the factors that allow biofilm's survival and persistence, as well as to contribute to understanding host specificity in the Vibrio fischeri-Euprymna spp. symbiosis.;Biofilm survival was studied when V. fischeri communities were subjected to different abiotic factors (such as salt concentration, temperature, static/dynamic conditions, and carbon source availability) and multiple protozoan bacteriovores (Tetrahymena, Rynchomonas, Neobodo). I found supporting evidence that biofilms are extremely plastic, and they are capable to endure multiple stresses using different strategies depending of the nature of the strain and the type of stress.;Molecular characterization of biofilms was accomplished through the study of different structural and regulatory genes, as well as characterization of molecular patterns using a meta-proteomic approach. My results confirmed that multiple genes are responsible of biofilm formation and host colonization, and that biofilms expressed multiple proteinaceous components responsible of bacterial stress responses, biosynthesis of matrix and transporters, as well as detection of anabolic and catabolic metabolites that are specific for V. fischeri communities. Genes that have been reported to be important in biofilm formation were manipulated and mobilized in two closely related V. fischeri strains, and used in infection studies in two different species of Euprymna. My results indicate that multiple biofilm-related loci are responsible for efficient host colonization and can dramatically alter host range.;Overall my thesis provides a strong framework of the study of the peculiar lifestyle of microbes that is the formation of a biofilm, and contributes to understand what molecular components are crucial for formation of biofilms, host colonization and host specificity in beneficial associations. |
