Vertebrate mucus stimulates biofilm development and upregulates iron acquisition genes in Flavobacterium columnare

Authors: Lange, Miles; Farmer, Bradley; Abernathy, Jason

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2019
Publication Date: 11/10/2019
Citation: Lange, M.D., Farmer, B.D., Abernathy, J.W. 2019. Vertebrate mucus stimulates biofilm development and upregulates iron acquisition genes in Flavobacterium columnare. Journal of Fish Diseases. https://doi.org/10.1111/jfd.13103.
DOI: https://doi.org/10.1111/jfd.13103

Interpretive Summary: Flavobacterium columnare is the bacterium responsible for producing the fish disease known as columnaris. Columnaris disease has had a significant impact on the production of different freshwater finfish species. Because of these losses, efforts to understand the biological processes of F. columnare including the development of biofilms and their contribution to disease are ongoing. The current work sought to evaluate the effect of mucus derived from different sources on the formation of biofilms among different F. columnare isolates. F. columnare has long been observed to cause extensive lesions on the skin and gills through circumventing the mucus layer which then allows biofilm formation to occur. Our data indicates the addition of different vertebrate mucus (catfish, tilapia or pig) at varying concentrations significantly stimulates F. columnare biofilm formation. This result could be observed among both genomovar I and II F. columnare isolates. We also demonstrated that differential gene expression of iron acquisition systems was observed between the planktonic cells and biofilms when stimulated with fish mucus. This work will no doubt serve as a basis for future studies on understanding how bacterial cell signaling leads to the development of biofilms and ultimately in the in vivo progression of columnaris disease.

Technical Abstract: Columnaris disease is responsible for substantial losses throughout the production of many freshwater fish species. One of the ways in which the bacterium Flavobacterium columnare is so effective in initiating disease is through the formation of biofilms on fish skin and gills. To further explore the interaction between host factors and bacterial cells, we assayed the ability of vertebrate mucus to enhance F. columnare biofilm development. Different concentrations of catfish, tilapia and pig mucus (5-60 µg/mL) increased biofilm growth at varying degrees among F. columnare isolates. Our data suggest that vertebrate mucus acts as a signaling molecule for the development of F. columnare biofilms; however, there are clear disparities in how individual isolates respond to different mucus fractions to stimulate biofilms. The expression of iron acquisition genes among two genomovar II isolates showed that ferroxidase, TonB receptor, and the siderophore synthetase gene were all significantly upregulated among F. columnare biofilms. Interestingly, the siderophore acetyltransferase gene was only shown to be significantly upregulated in one of the genomovar II isolates. This work provides insight into our understanding of the interaction between F. columnare and vertebrate mucus, which likely contributes to the growth of planktonic cells and the transition into biofilms.