Deciphering the Molecular Basis for Attenuation of Flavobacterium columnare Strain Fc1723 Used as Modified Live Vaccine against Columnaris Disease.

Wenlong Cai,Covadonga R Arias

doi:10.3390/vaccines9111370

Wenlong Cai, Covadonga R Arias

Open Access

https://doi.org/10.3390/vaccines9111370

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Journal: Vaccines	Publication Date: Nov 22, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: City University of Hong Kong, Auburn University

Abstract

Vaccines are widely employed in aquaculture to prevent bacterial infections, but their use by the U.S. catfish industry is very limited. One of the main diseases affecting catfish aquaculture is columnaris disease, caused by the bacterial pathogen Flavobacterium columnare. In 2011, a modified-live vaccine against columnaris disease was developed by selecting mutants that were resistant to rifampin. The previous study has suggested that this vaccine is stable, safe, and effective, but the mechanisms that resulted in attenuation remained uncharacterized. To understand the molecular basis for attenuation, a comparative genomic analysis was conducted to identify specific point mutations. The PacBio RS long-read sequencing platform was used to obtain draft genomes of the mutant attenuated strain (Fc1723) and the parent virulent strain (FcB27). Sequence-based genome comparison identified 16 single nucleotide polymorphisms (SNP) unique to the mutant. Genes that contained mutations were involved in rifampin resistance, gliding motility, DNA transcription, toxin secretion, and extracellular protease synthesis. The results also found that the vaccine strain formed biofilm at a significantly lower rate than the parent strain. These observations suggested that the rifampin-resistant phenotype and the associated attenuation of the vaccine strain result from the altered activity of RNA polymerase (RpoB) and possible disrupted protein secretion systems.

Highlights

Flavobacterium columnare is the causative agent of columnaris disease, which can infect a broad range of fish hosts, including wild, cultured and ornamental species [1]
Contigs of each genome were generated with Hierarchical Genome Assembly Process (HGAP) de novo assembly analysis application
Sixteen point mutations were identified in the vaccine strain

Summary

Introduction

Flavobacterium columnare is the causative agent of columnaris disease, which can infect a broad range of fish hosts, including wild, cultured and ornamental species [1]. Meta-genomic analysis of F. columnare revealed that the species is capable of denitrification, which could allow for anaerobic growth in pond sediments [6]. Since the eradication of F. columnare from aquaculture systems is very unlikely, prevention practices are the best approach to reduce the incidence of columnaris disease in farms. It is well known that the use of vaccines in fish farms contributes to more sustainable production systems by eliminating or reducing antibiotic use [7]. There is a commercial, live attenuated vaccine against columnaris disease under the trade name AQUAVAC-COLTM (Merck Animal Health, Madison, NJ, USA). Its efficacy has been questioned, and it is not widely used by farmers [10]

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Results

Conclusion