Siderophores produced by the fish pathogen Flavobacterium columnare strain MS-FC-4 are not essential for its virulence

Authors: CONRAD, RACHEL - University Of Wisconsin; Evenhuis, Jason; Lipscomb, Ryan; Birkett, Clayton; MCBRIDE, MARK - University Of Wisconsin

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2022
Publication Date: 8/15/2022
Citation: Conrad, R.A., Evenhuis, J., Lipscomb, R.S., Birkett, C., McBride, M.J. 2022. Siderophores produced by the fish pathogen Flavobacterium columnare strain MS-FC-4 are not essential for its virulence. Applied and Environmental Microbiology. 88(17). Article e00948-22. https://doi.org/10.1128/aem.00948-22.
DOI: https://doi.org/10.1128/aem.00948-22

Interpretive Summary: Iron acquisition, uptake and regulation is important for normal bacterial function. Several genes related to iron uptake and regulation were identified in Flavobacterium columnare, an important bacterial fish pathogen. Some of these genes were mutated to determine how function was impacted in F. columnare. Growth was reduced in bacteria where iron regulation and uptake genes were mutated and grown in iron deficient media. No change was observed comparing virulence between mutated bacteria and the non-mutated parent strain against either rainbow trout or zebrafish. This study furthers our understanding of virulence mechanisms in F. columnare and suggests that genetic manipulation of iron uptake and regulation genes in this pathogen is unlikely to yield an effective live-attenuated vaccine.

Technical Abstract: Flavobacterium columnare causes columnaris disease in wild and aquaculture-reared freshwater fish. F. columnare virulence mechanisms are not well understood, and current methods to control columnaris disease are inadequate. Iron acquisition from the host is important for pathogenicity and virulence of many bacterial pathogens. F. columnare iron acquisition has not been studied in detail. We identified genes predicted to function in siderophore production for ferric iron uptake. Genes predicted to encode proteins needed for siderophore synthesis, export, uptake, and regulation were deleted. The mutants were examined for defects in siderophore production, for growth defects in iron-limited conditions, and for virulence against zebrafish and rainbow trout. Mutants lacking all siderophore activity were obtained. These mutants displayed growth defects when cultured under iron-limited conditions, but they retained virulence against zebrafish and rainbow trout similar to that exhibited by the wild type, indicating that siderophores are not required for F. columnare virulence under the conditions tested.