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Research Project: Pathogen Characterization, Host Immune Response and Development of Strategies to Reduce Losses to Disease in Aquaculture

Location: Aquatic Animal Health Research

Title: The type IX secretion system is required for virulence of the fish pathogen Flavobacterium columnare

Author
item Li, Nan - University Of Wisconsin
item Zhu, Yongtao - University Of Wisconsin
item Lafrentz, Benjamin
item Evenhuis, Jason
item Hunnicutt, David - St Norbert College
item Conrad, Rachel - University Of Wisconsin
item Barbier, Paul - University Of Wisconsin
item Gullstrand, C - St Norbert College
item Roet, J - St Norbert College
item Powers, J - St Norbert College
item Kulkami, S - University Of Wisconsin
item Erbes, D - University Of Wisconsin
item Garcia, Julio
item Nie, P - Chinese Academy Of Agricultural Sciences
item Mcbride, Mark - University Of Wisconsin

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2017
Publication Date: 11/24/2017
Citation: Li, N., Zhu, Y., LaFrentz, B.R., Evenhuis, J., Hunnicutt, D.W., Conrad, R.A., Barbier, P., Gullstrand, C.W., Roet, J.E., Powers, J.L., Kulkami, S.S., Erbes, D.H., Garcia, J.C., Nie, P., McBride, M.J. 2017. The type IX secretion system is required for virulence of the fish pathogen Flavobacterium columnare. Applied and Environmental Microbiology. 83(23):e01769-17. https://doi.org/10.1128/AEM.01769-17.
DOI: https://doi.org/10.1128/AEM.01769-17

Interpretive Summary: Columnaris disease is responsible for large losses in multiple fish species important to the U.S. aquaculture industry. The mechanisms Flavobacterium columnare bacteria use to cause columnaris disease in freshwater fish are unknown. A protein secretion system that delivers protein toxins to the outside of the bacterial cell was found to be important in the disease process. Deletion of two genes (gldN and porV) that are required for secretion eliminated the ability of the bacterium to cause disease in multiple fish species. Normal bacterial cells secreted toxins that killed the fish, but the mutants failed to do this. This work helps us understand the virulence mechanisms of F. columnare and identifies potential target genes for vaccine development to prevent outbreaks of columnaris disease in aquaculture systems.

Technical Abstract: Flavobacterium columnare, a member of the phylum Bacteroidetes, causes columnaris disease in wild and aquaculture-reared freshwater fish. The mechanisms responsible for columnaris disease are not known. Many members of the phylum Bacteroidetes use type IX secretion systems (T9SSs) to secrete enzymes, adhesins, and proteins involved in gliding motility. The F. columnare genome has all of the genes needed to encode a T9SS. gldN, which encodes a core component of the T9SS, was deleted in wild type strains of F. columnare. The F. columnare Delta gldN mutants were deficient in secretion of several extracellular proteins and lacked gliding motility. The Delta gldN mutants were avirulent in zebrafish, channel catfish, and rainbow trout, and complementation restored virulence. PorV is required for secretion of a subset of proteins targeted to the T9SS. A F. columnare Delta porV mutant exhibited gliding motility but was avirulent. Cell-free spent media from exponentially growing cultures of wild type and complemented strains caused rapid mortality but spent media from Delta gldN and Delta porV mutants did not, suggesting that soluble toxins are secreted by the T9SS.