Both msa genes in Renibacterium salmoninarum are needed for full virulence in bacterial kidney disease

Area of Science:

• Bacteriology
• Fish Pathology
• Molecular Biology

Background:

• Renibacterium salmoninarum causes bacterial kidney disease in salmonids.
• The major soluble antigen (MSA) protein is a suspected virulence factor.
• Two chromosomal loci, msa1 and msa2, encode the MSA gene.

Purpose of the Study:

• To investigate the role of msa1 and msa2 genes in R. salmoninarum virulence.
• To determine the effect of gene disruption on MSA protein expression and fish disease.

Main Methods:

• Insertion-duplication mutagenesis was used to disrupt msa1 and msa2 genes.
• MSA protein expression was analyzed in broth cultures.
• Virulence of mutant strains was assessed in juvenile chinook salmon (Oncorhynchus tshawytscha) via intraperitoneal challenge.

Main Results:

• Disruption of msa1 or msa2 did not alter MSA protein expression in vitro.
• Mutant strains exhibited severely attenuated virulence in chinook salmon.
• In vivo expression or function of MSA appears critical for disease development.

Conclusions:

• The msa1 and msa2 genes are essential for R. salmoninarum virulence in salmonids.
• MSA protein plays a crucial role in bacterial kidney disease pathogenesis.
• Gene disruption impacts in vivo virulence, not necessarily in vitro protein production.