Diversity of insect trypanosomatids assessed from the spliced leader RNA and 5S rRNA genes and intergenic regions.

We have determined the sequences of 5S rRNA and spliced leader (SL) RNA genes, and adjacent intergenic regions for representatives of all known trypanosomatid genera parasitizing insects. The genetic loci have been analyzed separately as well as by a combined approach. Several isolates, assigned by morphology to different genera (Leptomonas spp., Blastocrithidia spp.), seem to belong to a single species with an unexpectedly wide host and geographical range. An unnamed trypanosomatid isolated from rats in Egypt was found to belong to the genus Herpetomonas, so far associated with insect hosts only. It is closely related to Herpetomonas ztiplika, a parasite of a blood-sucking biting midge. Apparently several different trypanosomatid species can infect one insect species, as exemplified by Leptomonas sp. PL and Wallaceina sp. Wsd, which were isolated from different specimens of Salda littoralis on the same locality and day. However, since the same species of Leptomonas was obtained from insect hosts belonging to different genera, some insect trypanosomatids may have low host specificity. Our data revealed additional discrepancies between molecular phylogenetic data and cell morphology, rendering current trypanosomatid taxonomy unreliable.

Phylogeny of the kinetoplastida: taxonomic problems and insights into the evolution of parasitism

To further investigate phylogeny of kinetoplastid protozoa, the sequences of small subunit (18S) ribosomal RNA of nine bodonid isolates and ten isolates of insect trypanosomatids have been determined. The root of the kinetoplastid tree was attached to the branch of Bodo designis and/or Cruzella marina. The suborder Trypanosomatina appeared as a monophyletic group, while the suborder Bodonina was paraphyletic. Among bodonid lineages, parasitic organisms were intermingled with free-living ones, implying multiple transitions to parasitism and supporting the `vertebrate-first hypothesis'. The tree indicated that the genera Cryptobia and Bodo are artificial taxa. Separation of fish cryptobias and Trypanoplasma borreli as different genera was not supported. In trypanosomatids, the genera Leptomonas and Blastocrithidia were polyphyletic, similar to the genera Herpetomonas and Crithidia and in contrast to the monophyletic genera Trypanosoma and Phytomonas. This analysis has shown that the morphological classification of kinetoplastids does not in general reflect their genetic affinities and needs a revision

Genomic rearrangements in trypanosomatids: an alternative to the "One Gene" evolutionary hypothesis?

Most molecular trees of trypanosomatids are based on point mutations within DNA sequences. In contrast, there are very few evolutionary studies considering DNA (re) arrangement as genetic characters. Waiting for the completion of the various parasite genome projects, first information may already be obtained from chromosome size-polymorphism, using the appropriate algorithms for data processing. Three illustrative models are presented here. First, the case of Leishmania (Viannia) braziliensis/L. (V.) peruviana is described. Thanks to a fast evolution rate (due essentially to amplification/deletion of tandemly repeated genes), molecular karyotyping seems particularly appropriate for studying recent evolutionary divergence, including eco-geographical diversification. Secondly, karyotype evolution is considered at the level of whole genus Leishmania. Despite the fast chromosome evolution rate, there is qualitative congruence with MLEE- and RAPD-based evolutionary hypotheses. Significant differences may be observed between major lineages, likely corresponding to major and less frequent rearrangements (fusion/fission, translocation). Thirdly, comparison is made with Trypanosoma cruzi. Again congruence is observed with other hypotheses and major lineages are delineated by significant chromosome rearrangements.