The Type IX Secretion System Is Required for Virulence of the Fish Pathogen Flavobacterium psychrophilum

• Published in: Applied and environmental microbiology Vol. 86; no. 16; p. 1
• Main Authors: Barbier, Paul, Rochat, Tatiana, Mohammed, Haitham H, Wiens, Gregory D, Bernardet, Jean-François, Halpern, David, Duchaud, Eric, McBride, Mark J
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 03-08-2020
• Subjects: Adhesins; Animals; Aquaculture; Bacterial Secretion Systems - genetics; Bacterial Secretion Systems - metabolism; Cell surface; Complementation; Fish; Fish Diseases - microbiology; Flavobacteriaceae Infections - microbiology; Flavobacteriaceae Infections - veterinary; Flavobacterium - genetics; Flavobacterium - pathogenicity; Flavobacterium - physiology; Flavobacterium psychrophilum; Gene deletion; Genetics and Molecular Biology; Genomes; Gliding; Life Sciences; Microbiology and Parasitology; Motility; Mutants; Oncorhynchus mykiss; Pathogens; Peptidases; Proteins; Proteolysis; Secretion; Trout; Virulence; Virulence factors; Virulence Factors - genetics; Flavobacterium; rainbow trout; virulence; protein secretion; fish pathogen; Protein secretion; Virulence; Fish pathogen; Rainbow trout
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.00799-20

causes bacterial cold-water disease in wild and aquaculture-reared fish and is a major problem for salmonid aquaculture. The mechanisms responsible for cold-water disease are not known. It was recently demonstrated that the related fish pathogen,
, requires a functional type IX protein secretion system (T9SS) to cause disease. T9SSs secrete cell surface adhesins, gliding motility proteins, peptidases, and other enzymes, any of which may be virulence factors. The
genome has genes predicted to encode components of a T9SS. Here, we used a SacB-mediated gene deletion technique recently adapted for use in the
to delete a core
T9SS gene,
The Δ
mutant cells were deficient for secretion of many proteins in comparison to wild-type cells. Complementation of the mutant with wild-type
on a plasmid restored secretion. Compared to wild-type and complemented strains, the Δ
mutant was deficient in adhesion, gliding motility, and extracellular proteolytic and hemolytic activities. The Δ
mutant exhibited reduced virulence in rainbow trout and complementation restored virulence, suggesting that the T9SS plays an important role in the disease.
Bacterial cold-water disease, caused by
, is a major problem for salmonid aquaculture. Little is known regarding the virulence factors involved in this disease, and control measures are inadequate. A targeted gene deletion method was adapted to
and used to demonstrate the importance of the T9SS in virulence. Proteins secreted by this system are likely virulence factors and targets for the development of control measures.