Insights into the diversity, adaptation and virulence of fish-patogenic Streptococcus agalactiae strains through transcriptomic and proteomic analysis

Abstract

Streptococcus agalactiae (GBS) infection is one the main diseases diagnosed in worldwide fish farming. This bacterium is a major pathogen for the Nile tilapia, a global commodity of the aquaculture sector, causing outbreaks of septicemia and meningoencephalitis. The Brazilian GBS fish strains have distinct known genotypes, when evaluated by the MLST technique, predominantly the ST-260, ST-927 and the non-typeable lineage. Considering the evolutionary relationship between these genotypes and for representing the major lineages that infects fish in Brazil, it becomes necessary to understand the specific characteristics of metabolism, adaptation and pathogenicity of these genetic groups as well as their relationships with the aquatic host. In order to evaluate the transcript and protein expression on GBS strains, two experiment trials were performed. The first trial evaluated the pan-proteome of these same genotypes, compared the differential expression of proteins identified between isolates from fish and human using a LCUDMSE, and identified in silico conserved antigenic proteins that can be used as target in vaccine design. The second trial aimed to evaluate the transcriptome and proteome of a Brazilian fishadapted GBS strain, being cultured in vitro under different temperatures and analyzed using microarray and liquid chromatography-mass spectrometry label-free shotgun (LC-HDMSE) approaches. In the first trial, a total of 1,065 protein clusters corresponded to pan-proteome of GBS fish strains, being 989 identified in all GBS fish strains (core proteome), 62 shared by at least two strains (accessory proteome) and 14 were exclusively expressed to each strain. The high degree of conservation among strains with different STs suggests that monovalent vaccines may be effective against different genetic variants. We also observed that the identified proteins in pan-proteome reflect the adaptive ability of the GBS fish strains in the response to stress factors imposed by the aquatic environment allowing the bacterial survival and multiplication in the fish host. A total of 215 and 269 proteins from GBS fish strains were up- and down-regulated, respectively, in comparison to human isolate. Regardless of the similarities in protein content, the global protein expression of the GBS human strain was different from the GBS fish strains suggesting distinct adaptations to mammal and fish host at the proteome level. In the second trial, the transcriptomic analysis detected 107 genes as being differentially expressed in SA53 at 32 ºC when compared with 22 ºC. While in proteomic analysis were detected 81 differentially expressed proteins. The results demonstrated that the temperature regulates the differential expression of genes and proteins, mainly those involved with the expression of virulence factors, metabolism, adaptation and bacterial resistance to thermal stress. Together, the two experiments provided news insights into the diversity, adaptation and virulence of fish-pathogenic GBS strains through transcriptomic and proteomic analysis.