|LI, CHAO - AUBURN UNIVERSITY|
|Barnett, Louis - Matt|
|PEATMAN, ERIC - AUBURN UNIVERSITY|
Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2014
Publication Date: 2/23/2015
Citation: Beck, B.H., Li, C., Farmer, B.D., Barnett, L.M., Lange, M.D., Peatman, E. 2015. A comparison of high and low virulence Flavobacterium columnare strains reveals differences in iron acquisition components and responses to iron restriction. Journal of Fish Diseases. DOI: 10.1111/jfd.12343.
Interpretive Summary: Flavobacterium columnare, the causative agent of columnaris disease causes substantial mortality worldwide in numerous freshwater finfish species. Due to its global significance, a better understanding of the factors that contribute to virulence (the ability to cause disease) is urgently needed. One emerging area of interest is the study of how columnaris disease-causing bacteria acquire iron from host fish. In the present study, we compared iron uptake processes in two different strains of columnaris with different levels of virulence; one highly virulent and one moderately virulent strain. We found that the highly virulent strain showed a heightened ability to acquire iron, and that iron starvation could prevent the moderately virulent strain from causing disease. Our findings provide new insight into iron uptake and pathogen virulence, and offer promising new targets for columnaris prevention and treatment.
Technical 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.