Phylogenetic Analysis of the rfb Locus Genes of the Genus Leptospira of Serogroups Serjoe, Mini and Hebdomadis

Abstract

Leptospirosis is a zoonosis of great impact on public health since it is considered a notifiable disease occurring mainly in tropical regions with poor sanitation and vulnerable socioeconomic conditions. It is caused by bacteria of the genus Leptospira and phylum Spirochaetes and contamination occurs through direct or indirect contact with the contaminating agent. In addition to taxonomic classification, which is performed through sequencing and the analysis of some marker genes, such as 16S rRNA and secY, they are usually classified based on their antigenic characteristics into serogroups and serovars. This kind of classification is largely applied in epidemiological studies and vaccine development. Despite its importance, few studies have been conducted to understand the evolutionary dynamics of the emergence or change of serology in this genus. In view of this, we applied phylogenetic methods in order to understand the evolutionary processes involving the serology of the genus. To this end, sequences of genes comprising the rfb locus from samples of serogroups Sejroe, Mini, and Hebdomadis (34 samples) were extracted and submitted to the phylogenetic pipeline, resulting in the inference of 75 maximum likelihood trees. Topology tests showed that most of the gene trees are significantly different from the species tree. We could depict the occurrence of lateral gene transfer between L. borgpetersenii and L. kirschneri; and L. interrogans and L. weilli. In this analysis, no evidence was found for the lateral gene transfer between samples of the Hardjo serovar of L. interrogans and L. borgpetersenii. Thus, it is also suggested that the occurrence of horizontal transfer of genes from the rfb locus between distinct species is less frequent than expected.