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Background  Proline racemase (PRAC) enzymes of  Trypanosoma cruzi  ( Tc PRAC), the agent of Chagas disease, and  Trypanosoma vivax  ( Tv PRAC), the agent of livestock trypanosomosis, have been implicated in the B-cells polyclonal activation contributing to immunosuppression and the evasion of host defences. The similarity to prokaryotic PRAC and the absence in  Trypanosoma brucei  and  Trypanosoma congolense  have raised many questions about the origin, evolution, and functions of trypanosome PRAC ( Try PRAC) enzymes.    Findings  We identified  Try PRAC homologs as single copy genes per haploid genome in 12 of 15  Trypanosoma  species, including  T. cruzi  and  T. cruzi marinkellei ,  T. dionisii, T. erneyi, T. rangeli ,  T. conorhini  and  T. lewisi,  all parasites of mammals. Polymorphisms in  Tc PRAC genes matched  T. cruzi  genotypes: TcI-TcIV and Tcbat have unique genes, while the hybrids TcV and TcVI contain  Tc PRACA and  Tc PRACB from parental TcII and TcIII, respectively .  PRAC homologs were identified in trypanosomes from anurans, snakes, crocodiles, lizards, and birds. Most trypanosomes have intact PRAC genes.  T. rangeli  possesses only pseudogenes, maybe in the process of being lost.  T. brucei, T. congolense  and their allied species ,  except the more distantly related  T. vivax , have completely lost PRAC genes .Conclusions  The genealogy of  Try PRAC homologs supports an evolutionary history congruent with the  Trypanosoma  phylogeny. This finding, together with the synteny of PRAC loci, the relationships with prokaryotic PRAC inferred by taxon-rich phylogenetic analysis, and the absence in trypanosomatids of any other genera or in bodonids or euglenids suggest that a common ancestor of  Trypanosoma  gained PRAC gene by a single and ancient horizontal gene transfer (HGT) from a Firmicutes bacterium more closely related to  Gemella  and other species of Bacilli than to  Clostridium  as previously suggested. Our broad phylogenetic study allowed investigation of  Try PRAC evolution over long and short timescales.  Try PRAC genes diverged to become species-specific and genotype-specific for  T. cruzi  and  T. rangeli,  with resulting genealogies congruent with those obtained using vertically inherited genes. The inventory of  Try PRAC genes described here is the first step toward the understanding of the roles of PRAC enzymes in trypanosomes differing in life cycles, virulence, and infection and immune evasion strategies.    Electronic supplementary material  The online version of this article (doi:10.1186/s13071-015-0829-y) contains supplementary material, which is available to authorized users.

parasites and vectors

Phylogenetic and syntenic data support a single horizontal transference to a Trypanosoma ancestor of a prokaryotic proline racemase implicated in parasite evasion from host defences