Análise do pan­-genoma de cepas de Streptococcus agalactiae isoladas de Tilápia do Nilo (Oreochromis niloticus)

Abstract

Streptococcosis, caused by Streptococcus agalactiae, is one of the main causes of death and economic losses in Nile tilapia (Oreochromis niloticus) farms around the world. Therefore, it is necessary genomic and pathogenicity studies to have a better understanding of the infection process and the pathogenic potential of this microorganism. Pangenome analysis is a study tool with great potential to deeply analyze the similarities and differences of genomes among strains of the same species. Although studies on the pangenome of S. agalactiae have already been published, there are no studies available in the literature that focus on the pangenome of Nile tilapia isolated strains. Thus, this research aims to investigate the pangenome of 49 strains of S. agalactiae isolated from Nile tilapia. For that, the genomes were analyzed by KBase Predictive Biology software, which used mainly the OrthoMCL and FastTree2 algorithms for orthologues prediction and phylogenetic analysis of the strains, respectively. The genomic comparison showed that, in general, the genomes of the 49 strains of S. agalactiae are highly conserved, but exhibit several shared and exclusive regions, which guarantee genetic diversity. The phylogenetic study showed that the strains were grouped according to the capsular serotype. In the pan­genome analysis, 5154 gene families were found, with 1277 families belonging to the core genome and 3877 to the accessory genome. The core genome was composed mainly of genes related to essential cell functions, such as protein metabolism and cell wall, while the accessory genome showed both essential genes and regions that could offer advantages to cells. The comparative study among Maranhão, Recife, and E8ang2 strains revealed the presence of important virulence­associated genes in the E8ang exclusive genome and in the shared genome of Maranhão and Recife. With these results, it was possible to obtain a general profile of the studied group pan­genome and to characterize the genomic regions that make up the core and accessory genomes, as well as understand the phylogenetic profile of the 49 strains. These data show the importance of studying S. agalactiae strains isolated from Nile tilapia, besides showing the need for further studies that deepen the genomic characterization of these pathogens.