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Title: Flagella biosynthesis and regulation by the Rcs pathway within the fish pathogen Yersinia ruckeri during infection

Author
item Snyder, Anna
item Welch, Timothy - Tim

Submitted to: Pittsburgh Bacterial Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/7/2015
Publication Date: 3/7/2015
Citation: Snyder, A.K., Welch, T.J. 2015. Flagella biosynthesis and regulation by the Rcs pathway within the fish pathogen Yersinia ruckeri during infection. Pittsburgh Bacterial Meeting. Paper No. 50A.

Interpretive Summary:

Technical Abstract: The gram-negative Enterobacterium Yersinia ruckeri is the etiologic agent of enteric redmouth disease (ERM) within farmed rainbow trout (Oncorhynchus mykiss, Walbaum). Over the past decade, there has been an increase in the prevalence of non-motile variants of Y. ruckeri and the appearance of these variants has correlated to outbreaks in previously vaccinated fish. This observation suggests that the loss of motility either increases Y. ruckeri virulence or decreases this pathogen's sensitivity to vaccination. The goal of this study was to determine the importance of the Y. ruckeri flagellar apparatus and its regulation to the infection process. First, experimental challenges showed that there was no competitive advantage for non-motility in naïve or vaccinated fish. In support of these findings, reverse transcriptional analysis of the flagellar locus fliC revealed decreasing expression throughout the course of infection, which was subsequently up-regulated upon host mortality. We hypothesize that the observed repression of flagella biosynthesis during infection is important for virulence, as flagellin (FliC), the major structural component of the flagellum, has been shown to cause immune stimulation. The Rcs pathway was then investigated as a potential negative regulator for flagella biosynthesis, as a putative RcsB-box was identified in the promoter region of the flagellar master regulatory operon¸ flhDC. A null mutation in the response regulator rcsB was constructed by allelic exchange and its motility and virulence phenotypes were examined. Y. ruckeri is a genetically tractable fish pathogen and thus serves as a valuable model to study the molecular mechanisms controlling the regulation flagellar biosynthesis and its influence on virulence. ERM outbreaks can significantly impact aquaculture and factors influencing virulence may be utilized for enhanced disease prevention or control strategies.