title: A comparison of high- and low-virulence Flavobacterium columnare strains reveals differences in iron acquisition components and responses to iron restriction.
abstract: Flavobacterium columnare, the causative agent of columnaris disease causes substantial mortality worldwide in numerous freshwater finfish species. Due to its global significance, an improved understanding of the factors that contribute to virulence is urgently needed. In a laboratory challenge, we found that significantly greater mortality was observed in channel catfish Ictalurus punctatus (Rafinesque) challenged with isolate LSU-066-04 (LSU) as compared to fish challenged with isolate LV-359-01 (LV). Strikingly, mortality was 100% in LSU-challenged fish, with all fish dying within the first 24 h after challenge, while mortality in the LV-challenged group was significantly lower with 26.7% of fish dying on days 1-4 post-challenge. There were no differences in initial bacterial adhesion between the isolates at 1-2 h post-challenge; however, by 4 h LSU-challenged fish had a greater bacterial load on the gill. Next, to better understand this variation in virulence, we examined transcriptional and functional attributes related to iron acquisition. The isolates were differentially sensitive to iron restriction both in vitro and in vivo and the basal expression of TonB family member genes and a ferroxidase gene differed significantly. Our findings provide new insight into iron uptake and pathogen virulence, and offer promising new targets for columnaris prevention and treatment.
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Harry K. Dupree Stuttgart National Aquaculture Research Center, Stuttgart, AR, USA.
authors.forename: B H
authors.initials: BH
authors.lastname: Beck
authors.affiliation: School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, USA.
authors.forename: C
authors.initials: C
authors.lastname: Li
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Harry K. Dupree Stuttgart National Aquaculture Research Center, Stuttgart, AR, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Farmer
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Harry K. Dupree Stuttgart National Aquaculture Research Center, Stuttgart, AR, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Barnett
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, Harry K. Dupree Stuttgart National Aquaculture Research Center, Stuttgart, AR, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Lange
authors.affiliation: School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, USA.
authors.forename: E
authors.initials: E
authors.lastname: Peatman
mesh_terms: D000818:Animals; D001422:Bacterial Adhesion / Q000502:physiology; D005393:Fish Diseases / Q000382:microbiology* / Q000401:mortality; D029941:Fish Proteins / Q000235:genetics; D045826:Flavobacteriaceae Infections / Q000382:microbiology / Q000401:mortality / Q000662:veterinary*; D005417:Flavobacterium / Q000145:classification / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D005880:Gills / Q000382:microbiology; D007059:Ictaluridae / Q000382:microbiology; D007501:Iron / Q000378:metabolism*; D014774:Virulence / Q000235:genetics*
chemical_list: D029941:Fish Proteins; D007501:Iron
keywords: Flavobacterium columnare; columnaris disease; iron uptake; virulence