Treponema pallidum subsp. pallidum (TPA) is the etiological agent of syphilis, a sexually transmitted disease that has been resurgent in the last decades. TPA genome is highly conserved and very similar to that of the closely related T. pallidum subsp. pertenue (TPE) and T. pallidum subsp. endemicum (TEN), which cause the human treponematoses yaws and bejel, respectively. We have analyzed 75 complete genome sequences from the three T. pallidum subspecies looking for potential recombination events and to establish the role of natural selection in their evolution. We found 12 genes with 21 different recombination events. Only one recombination event per gene was detected except for genes of tp0136 and tp0326, which showed 7 and 4 events, respectively. All but one events (in tp0136) corresponded to inter-subspecies transfers (TPE/TEN to TPA). Clear evidence for natural selection acting on the recombinant genes was provided by significantly higher values of the non-synonymous/synonymous substitution rate in the recombinant regions than in the non-recombinant zones of those genes. Additionally, 14 non-recombinant genes with evidence of positive selection, and 23 non-recombinant genes with significantly more SNPs than expected were identified. These signals of natural selection were confirmed by additional tests in ten of the recombinant genes, 2 of the non-recombinant genes with abundant SNPs and in 1 of the other nonrecombinant genes with positive selection signal. The phylogenetic location of some of these events and their functional role suggest that both recombination and selection may have had an important role in the evolution of T. pallidum.

Resumen del trabajo presentado a la VII Biennial Congress of Sociedad Española de Biología Evolutiva (SEBE), celebrada en Sevilla (España) del 5 al 7 de febrero de 2020.

Peer reviewed