Transcriptome analysis of the fish pathogen Flavobacterium columnare in biofilm suggests calcium role in pathogenesis

Wenlong Cai,Covadonga R Arias,Leonardo De La Fuente

doi:10.1186/s12866-019-1533-4

Wenlong Cai, Covadonga R Arias + Show 1 more

Open Access

https://doi.org/10.1186/s12866-019-1533-4

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Journal: BMC microbiology	Publication Date: Jul 4, 2019
Citations: 10	License type: open-access

Affiliation: Auburn University

Abstract

BackgroundFlavobacterium columnare is the causative agent of columnaris disease that affects cultured freshwater fishes worldwide. F. columnare easily colonizes surfaces by forming biofilm, which helps the pathogen resist antibiotic and disinfectant treatments. Previously, we had shown that increasing concentrations of calcium (Ca2+) promoted biofilm formation by F. columnare. The objective of this study was to further characterize the role of Ca2+ on biofilm formation and to compare the transcriptome profiles of planktonic and biofilm cells.ResultsRNA-Seq analysis was conducted to identify genes that were differentially expressed between the following states: i) planktonic cells in control medium (P), ii) planktonic cells in calcium-enriched medium (P/Ca), and iii) biofilm cells in calcium-enriched medium (B/Ca). Overall, we identified 441 significant (FDR-adjusted p < 0.05, fold change > 2) differentially expressed genes (DEGs) between P and B/Ca samples; 112 significant DEGs between P/Ca and B/Ca samples, and 175 significant DEGs between P/Ca and P samples, corresponding to 15.87, 4.03 and 6.30% of the total protein-coding sequences, respectively. The significant DEGs fell into different functional categories including iron acquisition, oxidative stress response, extracellular protein secretion, and respiratory metabolism.ConclusionsOur results posit Ca2+ as a critical signal in regulating bacterial surface adhesion and biofilm formation in F. columnare. Living in biofilm elicited a shift in several metabolic pathways that allowed the cells to cope with oxidative stress and nutrient starvation. In addition, Ca2+ supplementation induced the expression of putative virulence factors in F. columnare, such as extracellular protein secretion and iron acquisition.

Highlights

Flavobacterium columnare is the causative agent of columnaris disease that affects cultured freshwater fishes worldwide
Ribonucleic acid (RNA) for whole transcriptome analysis of biofilms growing in control medium
At the other end of the spectrum, at 6.5 mM [Ca2+], cells grew in large clusters that quickly precipitated to the bottom after shaking ceased and there was no visible biofilm on the glass walls

Summary

Introduction

Flavobacterium columnare is the causative agent of columnaris disease that affects cultured freshwater fishes worldwide. F. columnare colonizes surfaces by forming biofilm, which helps the pathogen resist antibiotic and disinfectant treatments. We had shown that increasing concentrations of calcium (Ca2+) promoted biofilm formation by F. columnare. Flavobacterium columnare is a Gram negative bacterium that is the causative agent of columnaris disease in fish. This bacterial fish pathogen causes great economic losses in key aquaculture species worldwide such as channel catfish, tilapia, and trout [1]. Flavobacterium columnare is considered to be ubiquitous in freshwater environments including fish farms. Columnaris disease is transmitted horizontally by fish-to-fish contact and asymptomatic fish can vector the pathogen into a farm.

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