Comparative proteomic and genomic analysis of lactococcus garvieae and lactococcus petauri isolates from Turkey

Abstract

Piscine lactococcosis, a bacterial disease caused by Lactococcus garvieae, L. petauri and L. formosensis, induces mass mortalities in multiple farmed fish species globally. Following the identification of L. petauri as one of the emerging etiological agents of piscine lactococcosis, it was revealed that the majority of isolates previously recognized as L. garvieae actually belong to L. petauri. In this study, a total of 134 Lactococcus sp. isolates, including L. garvieae (n = 40) and L. petauri (n = 94) were analyzed. Differential identification of L. garvieae and L. petauri isolates was performed through basic sucrose fermentation and end-point PCR analysis using species- specific primer sequences. Comparative analysis of capsule formation in both species was conducted for the first time using transmission electron microscopy, whole-cell protein profile via 1D SDS-PAGE, antigenic protein characterization using Western blot analysis, and serological profile description by slide and microagglutination assays. Moreover, comprehensive genomic comparisons were made, deciphering overall genomic relatedness indices, virulence genes, and antimicrobial resistance patterns among these closely related species. Analysis showed microcapsule formation in some isolates of L. garvieae and L. petauri for the first time. While a high similarity rate was observed in the whole-cell protein profiles of these species, significant differences were identified among antigenic proteins. Variations between species were observed in slide agglutination and quantitative agglutination tests of L. garvieae and L. petauri field isolates. Capsule-deficient L. garvieae reference and field strain antisera did not agglutinate with each other; however, L. garvieae field strain antisera agglutinated with all L. garvieae field strains and L. petauri strains. These results indicated distinct serological characteristics of capsule-deficient L. garvieae isolates from Turkey compared to previously reported serological classifications. Genomic analyses revealed that none of the investigated L. garvieae and L. petauri isolates harbored the capsule gene cluster. In addition, Turkish isolates of L. garvieae and L. petauri clustered separately from isolates of other geographical origins but together with each other. This study aims to address the problem of lactococcosis, commonly referred to as "Summer Mortality Outbreak and Vaccine-Preventable Diseases," in a wide variety of cultured fish species through the selected L. garvieae and L. petauri isolates as potential vaccine strains.