Type IX Secretion System Effectors and Virulence of the Model Flavobacterium columnare Strain MS-FC-4
Nicole C. Thunes, Rachel A. Conrad, Haitham H. Mohammed, Yongtao Zhu, Paul Barbier, Jason P. Evenhuis, David Perez-Pascual, Jean-Marc Ghigo, Ryan S. Lipscomb, John R. Schneider, Nan Li, Devon H. Erbes, Clayton Birkett, Benjamin R. LaFrentz, Timothy J. Welch, Mark J. McBride
Abstract
Flavobacterium columnare causes columnaris disease in wild and aquaculture-reared freshwater fish and is a major problem for aquaculture. Little is known regarding the virulence factors involved in this disease, and control measures are inadequate. The type IX secretion system (T9SS) secretes many proteins and is required for virulence, but the secreted virulence factors are not known. We identified a strain of F. columnare (MS-FC-4) that is well suited for genetic manipulation. The components of the T9SS and the proteins secreted by this system were identified. Deletion of core T9SS genes eliminated virulence. Genes encoding 10 secreted proteins were deleted. Deletion of two peptidase-encoding genes resulted in decreased virulence in rainbow trout, and deletion of a cytolysin-encoding gene resulted in decreased virulence in rainbow trout and zebrafish. Secreted peptidases and cytolysins are likely virulence factors and are targets for the development of control measures.