Renibacterium salmoninarum p57 antigenic variation is restricted in geographic distribution and correlated with genomic markers

Abstract

The 57 kDa protein (p57) is an important diagnostic antigen that is implicated in the pathogenesis of salmonid bacterial kidney disease. Little is known about the nature and extent of antigenic variation in p57. Previously, we reported that p57 produced by Renibacterium salmoninarum Strain 684 contains a mutation that disrupts monoclonal antibody (MAb) 4C11 binding. In the present study, we examined MAb binding to a panel of 23 additional R. salmoninarum isolates obtained from diverse geographic locations to examine the prevalence of this variant and whether additional variability exists within other p57 epitopes. Six p57-specific MAbs (4C11, 4D3, 3H1, 4H8, 4D10 and 1A1) were used to probe dot and western blots to determine the relative expression, size and cellular association of p57. Full-length p57 was produced by all isolates, and for each isolate, the protein was associated with the bacterial cell surface. The epitopes recognized by 4 MAbs, 4D3, 4H8, 3H1 and 1A1, were conserved among all strains tested. The 4C11 epitope was absent in 5 of 8 strains originating from Norway, while the 4D10 epitope was partially disrupted in one isolate from British Columbia, Canada. The 5 Norwegian antigenic-variant strains appeared to be clonally related as they shared the following characteristics: one tandem repeat in the ETRA locus, a Sequovar-4 16-23S rRNA intervening DNA sequence, a larger Xho I fragment in the msa1 5' region, and absent msa3 gene. These results indicate that limited antigenic and genomic variation exists between strains and this variation appears geographically restricted in distribution. KEY WORDS: Renibacterium salmoninarum · msa gene P57 · Antigenic variation · Exact tandem repeat locus · ETR Resale or republication not permitted without written consent of the publisherDis Aquat Org 83: [123][124][125][126][127][128][129][130][131] 2009 . A single gene encoding p57 was originally cloned and designated msa for major soluble antigen (Chien et al. 1992), and subsequent investigation identified the presence of as many as 3 copies of msa in the bacterial genome depending on the R. salmoninarum isolate (Rhodes et al. 2004). Experimental reduction in gene copy number correlated with reduced virulence, thus demonstrating a crucial contribution of this protein to virulence (Rhodes et al. 2004, Coady et al. 2006. The coding regions of the msa1 and msa2 genes are identical, suggesting relatively recent gene duplication, and both genes are present in all characterized strains of R. salmoninarum (O'Farrell & Strom 1999, Wiens et al. 2002. msa3 has not yet been fully sequenced, but the flanking regions resemble msa1 and this gene has only been identified in a subset of strains originating from the US (Rhodes et al. 2004). Both msa1 and msa2 promoters are functional because integrated reporter plasmids were shown to be transcribed and translated during in vitro culture (Rhodes et al. 2002). Whether the msa3 promoter is functional has not been determined.We have previously reported antigenic variation...

Addressing viral and bacterial threats to salmon farming in Chile: historical contexts and perspectives for management and control

“…This variation could be associated with differences in the major antigen p57 protein (Wiens et al . ; Wiens & Dale ).…”

“…). Interestingly Wiens and Dale () suggested that some recombination must occur, at least between genes of the major soluble antigen (MSA) (a single Ala139 to Glu mutation in both genes). When these authors analysed R. salmoninarum isolated from Norway, 5 of the 8 contained this sequence variation overlapped at the same geographical area.…”

“…An assessment of 39 R. salmoninarum Chilean isolates revealed, regardless of host (Atlantic salmon or coho salmon), highly homogeneous phenotypes but varied hydrophobicity (10-90%), as found by hydrocarbon adhesions (Bethke et al 2017). This variation could be associated with differences in the major antigen p57 protein (Wiens et al 2002;Wiens & Dale 2009).…”

“…Two antigenic groups of R. salmoninarum have been reported (Band ın et al 1992), with antigenic variation in the secreted cell surface antigen p57 (also known as antigen F) (Wiens et al 2002). Interestingly Wiens and Dale (2009) suggested that some recombination must occur, at least between genes of the major soluble antigen (MSA) (a single Ala139 to Glu mutation in both genes). When these authors analysed R. salmoninarum isolated from Norway, 5 of the 8 contained this sequence variation overlapped at the same geographical area.…”

Renibacterium salmoninarum and Mycobacterium spp.: two bacterial pathogens present at low levels in wild brown trout (Salmo trutta fario) populations in Austrian rivers

“…salmoninarum is a facultative intracellular pathogen and several virulence factors have been identified [12]. P57 (57-kDa protein) is the best studied among these virulence factors and plays a significant role in cell agglutination and immune-suppression of the host [14][15][16][17]. Fish infected with R. salmoninarum can display external and internal clinical signs such as exophthalmia, blebs and blister on the epidermis with white or yellowish haemorrhagic fluid, petechiae and haemorrhages around the fins and lateral line, swelling of the kidney, heart, spleen, and liver alongside creamy-white and greyish granulomatous lesions on the surface of the viscera [18][19][20].…”