The emergence of human pathogens represents a major current global health concern. Characterization of the adaptations required for a given microorganism to emerge as a human pathogen is important for understanding epidemics, as we are typically aware of a pathogen's existence only after it has emerged, manifesting as an outbreak. Cholera is a severe diarrheal disease caused by the aquatic bacterium Vibrio cholerae O1 and is one paradigmatic example of disease emergence. Only a subset of V. cholerae strains can cause the disease while the majority of the strains cannot cause cholera symptoms. We found that toxigenic strains of V. cholerae encode allelic variations of core genes, termed Virulence Adaptive Polymorphisms (VAPs), that confer preadaptations towards the emergence of pathogenic traits. Interestingly, VAPs appear to naturally circulate in environmental populations of V. cholerae. One gene potentially encoding VAPs codes for the outer membrane protein U, OmpU. This major porin plays numerous roles in V. cholerae pathogenesis such as bile tolerance, antimicrobial peptide resistance or facilitates intestinal colonization. Interestingly, we found that these phenotypes appear to be allelic dependent and might provide a clue towards the emergence of toxigenic V. cholerae. To date, the distribution and prevalence of VAPs in environmental populations and the specific molecular mechanisms leading to their virulence preadaptations remain unknown. Here we examined the diversity of ompU alleles in natural V. cholerae populations in order to identify VAPs unique to the toxigenic allele of ompU to discern these preadaptations. We developed a comparative framework to address this by examining allelic variations of OmpU from an endemic population of V. cholerae that we identified for this study in Eastern Florida. We generated 14 isogenic mutant strains each encoding a unique ompU allele that largely covered the landscape of protein variability and examined their resistance profile to host antimicrobials. We determined the genotype to phenotype associations between these mutants and identified and experimentally confirmed four conserved domains that are unique to alleles of ompU that confer resistance to bile and other host antimicrobials. Interestingly, a mutant strain in which we exchanged the four domains of the clinical allele for those of a strain that was sensitive, exhibits a resistance profile closer to an OmpU deletion mutant. Our findings highlight the critical importance of allelic variations in the emergence of virulence adaptive traits and the suitability of our approach towards dissecting its emergence. This tractable approach can be naturally applied to other bacterial pathogens.
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Doctor of Philosophy (Ph.D.)
College of Medicine
Burnett School of Biomedical Sciences
Length of Campus-only Access
Doctoral Dissertation (Campus-only Access)
Grant, Trudy-Ann, "Molecular Adaptations for Intestinal Colonization in Vibrio cholerae" (2022). Electronic Theses and Dissertations, 2020-. 1377.
Restricted to the UCF community until December 2027; it will then be open access.