Genes and regulatory mechanisms controlling environmental survival strategies of the waterborne pathogen Vibrio cholerae.

摘要

Vibrio cholerae, the etiological agent of the severe diarrheal disease cholera, is a common inhabitant of the world's temperate and tropical waters. To cope the multitude of stresses found in these aquatic environments, V. cholerae has evolved many different survival mechanisms. Variations in gene content and regulation between strains allow for niche specialization within the species, and are possibly a determining factor behind fluxes of environmental populations. The work in this dissertation examines the underlying genetic and molecular components that are responsible for these mechanisms, focusing on biofilm formation.; It was found that while the morphology of the biofilms of environmental and clinical strains of V. cholerae are distinct from one another; the genes driving these processes are generally conserved between the strains. Also, many new genes involved in the biofilm formation process on abiotic surfaces in V. cholerae have been identified, including those known to have a role in molecular transport, vibrio polysaccharide (VPS) production and its regulation, amino acid metabolism, among others. However, many of these same genes are not required when biofilms are formed on biotic surfaces common in the marine environment (e.g. copepods and dinoflagellates). Under these conditions, only genes responsible for chemotaxis and motility are essential for V. cholerae's ability to colonize biotic surfaces. These results suggest that the distinct biofilms of different strains and within various environments is due to variability in the regulation of the expression of genes involved in biofilm formation and not variability in gene content. One of the genes identified to be involved for abiotic biofilm formation in multiple strains of V. cholerae was the tryptophanase gene. This work has shown that this gene's role appears to be indirect, as it is the indole by-product of the tryptophanase reaction, which can act as an extracellular signaling molecule that triggers an intracellular regulatory cascade and ultimately influences the expression of genes responsible for biofilm formation. This regulatory cascade is comprised of previously identified regulators of VPS production and the DksA protein, which appear to affect global gene regulation through altering intracellular concentrations of the second messenger, cyclic diguanulate (cdiGMP).