Caracterização dos elementos transponíveis em streptococcus agalactiae: uma análise comparativa em isolados de humanos, peixes e bovinos

Abstract

Streptococcus agalactiae, also known as Group B Streptococcus, is a bacterial pathogen with medical, veterinary, and aquaculture relevance. This species can colonize and cause disease in humans, bovines, and fish. Its ability to adapt to different hosts is associated with genomic plasticity and with the presence of mobile genetic elements, including transposable elements (TEs). This study aimed to characterize the TE repertoire of S. agalactiae through an integrated bioinformatic approach and to investigate TE distribution, sharing, exclusivity, and potential association with the evolution and adaptation of this species to different hosts. This study analyzed 159 S. agalactiae genomes, including 45 human isolates, 61 bovine isolates, and 53 fish isolates. TE identification was performed with ISEScan and complementary BLASTn similari ty searches against the ISfinder and TnCentral databases. The annotations were integrated and subjected to redundancy reduction with BEDTool s and CD-HIT. Comparative analyses were complemented by phylogenetic reconstructions based on the core genome and on Multilocus Sequence Typing (MLST) loci. The results identified 20 TE families and between 58 and 64 distinct TE elements, depending on the filtering strategy that was applied. Five TE families (IS3, IS5, IS21, IS30, and IS1182) and seven TE elements (ISSag5, ISSag2, IS1381A, IS861, ISSag9, ISSag8, an d ISSag3) were shared among the three host groups, which suggests a conserved core of mobile elements in the species. Bovine and human isolates showed higher TE diversity and abundance, whereas fish isolates showed a more restricted repertoire. The correla tion between genome size and TE content was positive and statistically significant in human isolates, which indicates that these elements may contribute to genome expansion in this host group. The phylogenetic analyses showed a monophyletic grouping of fish-associated serotype Ib lineages and a close relationship between fish and human serotype III isolates, which reinforces the zoonotic potential of some lineages. In addition, this study proposes the concept of the panTEgenome as the total TE repertoi re identified in a set of genomes, considering TE presence, absence, conservation, and host specificity. Overall, the results show that TEs are relevant components of S. agalactiae genomic plasticity and may represent molecular markers associated with adaptation to distinct ecological niches.