Growth, morphology and division of flagellates of the genus Trypanoplasma (Protozoa, Kinetoplastida) in vitro

Evolution of metabolic capabilities and molecular features of diplonemids, kinetoplastids, and euglenids

Background

The Euglenozoa are a protist group with an especially rich history of evolutionary diversity. They include diplonemids, representing arguably the most species-rich clade of marine planktonic eukaryotes; trypanosomatids, which are notorious parasites of medical and veterinary importance; and free-living euglenids. These different lifestyles, and particularly the transition from free-living to parasitic, likely require different metabolic capabilities. We carried out a comparative genomic analysis across euglenozoan diversity to see how changing repertoires of enzymes and structural features correspond to major changes in lifestyles.

Results

We find a gradual loss of genes encoding enzymes in the evolution of kinetoplastids, rather than a sudden decrease in metabolic capabilities corresponding to the origin of parasitism, while diplonemids and euglenids maintain more metabolic versatility. Distinctive characteristics of molecular machines such as kinetochores and the pre-replication complex that were previously considered specific to parasitic kinetoplastids were also identified in their free-living relatives. Therefore, we argue that they represent an ancestral rather than a derived state, as thought until the present. We also found evidence of ancient redundancy in systems such as NADPH-dependent thiol-redox. Only the genus Euglena possesses the combination of trypanothione-, glutathione-, and thioredoxin-based systems supposedly present in the euglenozoan common ancestor, while other representatives of the phylum have lost one or two of these systems. Lastly, we identified convergent losses of specific metabolic capabilities between free-living kinetoplastids and ciliates. Although this observation requires further examination, it suggests that certain eukaryotic lineages are predisposed to such convergent losses of key enzymes or whole pathways.

Conclusions

The loss of metabolic capabilities might not be associated with the switch to parasitic lifestyle in kinetoplastids, and the presence of a highly divergent (or unconventional) kinetochore machinery might not be restricted to this protist group. The data derived from the transcriptomes of free-living early branching prokinetoplastids suggests that the pre-replication complex of Trypanosomatidae is a highly divergent version of the conventional machinery. Our findings shed light on trends in the evolution of metabolism in protists in general and open multiple avenues for future research.

Host specificity, pathogenicity, and mixed infections of trypanoplasms from freshwater fishes

This work summarizes the results of the 8-year study focused on Trypanoplasma sp. parasitizing freshwater fishes in the vicinity of Kyiv, Ukraine. Out of 570 fish specimens of 2 different species analyzed, 440 individuals were found to be infected. The prevalence of infection ranged from 24 % in Abramis brama Linnaeus (freshwater bream) to 100 % in Cobitis taenia Linnaeus (spined loach). The level of parasitemia also varied between moderate in freshwater bream and very high in spined loach. Interestingly, no clinical manifestations of trypanoplasmosis were observed even in extremely heavily infected C. taenia. We hypothesize that different species may differ in evolutionary timing allowing for reciprocal adaptation of the members of the "host-parasite" system. Molecular analysis of the 18S rRNA sequences revealed that several specimens were simultaneously infected with at least two different trypanoplasm species. To the best of our knowledge, this is the first report of the mixed infection with fish trypanoplasms.

Ultrastructural changes during asexual multiple reproduction in Trichomonas vaginalis

Trichomonas vaginalis, a flagellated protozoan parasite, is commonly found in the genitourinary tract of humans. Its mode of reproduction has always been reported to be binary fission. The high parasite numbers seen in a relatively short period in in vitro cultures led us to believe that there must be other modes of reproduction. The present study for the first time provides transformational evidence at the ultrastructural level seen in tropohozoites of T. vaginalis undergoing a multiple asexual mode of reproduction. The findings show that the single cell with a nucleus is capable of dividing to as many as eight nuclei within the cytoplasmic body. Before the commencement of division, the nucleus remained round or ovoid in shape with condensed chromatin masses and only a few endoplasmic reticula surrounding the nucleus. During the division, the nucleus started to elongate and become irregular in shape with visible chromatin masses condensing with the accumulation of numerous endoplasmic reticula. Nuclear division gave rise to as many as eight nuclei within a cell, which could be seen to be connected by numerous endoplasmic reticula. In addition, a high number of hydrogenosomes and vacuoles can be seen in multinucleated T. vaginalis compared with single nucleated T. vaginalis. This study confirms that multiple modes of nuclear division do exist in T. vaginalis and are a precursor to progeny formation.

Phylogeny of trypanosomes as inferred from the small and large subunit rRNAs: implications for the evolution of parasitism in the trypanosomatid protozoa

Sequences of the small rRNA genes and partial sequences of the large rRNA genes were obtained by PCR amplification from a variety of vertebrate trypanosomes. The trypanosome species and hosts included Trypanosoma avium from a bird, T. rotatorium from an amphibian, T. boissoni from an elasmobranch, T. triglae from a marine teleost and T. carassii from a freshwater teleost. Phylogenetic relationships among these species and other representatives of the family Trypanosomatidae were inferred using maximum likelihood, maximum parsimony and evolutionary parsimony. The trypanosomatid tree was rooted using rRNA sequences from two species from the suborder Bodonina. All methods showed that the mammalian parasite, Trypanosoma brucei, constitutes the earliest divergent branch. The remaining trypanosomes formed a monophyletic group. Within this group, the bird trypanosome was grouped with T. cruzi, while the elasmobranch trypanosome and the two fish trypanosome species formed a group with an affinity to T. rotatorium. Our results provide no evidence for co-evolution of trypanosomatids and their hosts, either vertebrate or invertebrate. This suggests that evolution of trypanosomatids was accompanied by secondary acquisitions of hosts and habitats.

RNA editing and mitochondrial genomic organization in the cryptobiid kinetoplastid protozoan Trypanoplasma borreli

The bodonids and cryptobiids represent an early diverged sister group to the trypanosomatids among the kinetoplastid protozoa. The trypanosome type of uridine insertion-deletion RNA editing was found to occur in the cryptobiid fish parasite Trypanoplasma borreli. A pan-edited ribosomal protein, S12, and a novel 3'- and 5'-edited cytochrome b, in addition to an unedited cytochrome oxidase III gene and an apparently unedited 12S rRNA gene, were found in a 6-kb fragment of the 80- to 90-kb mitochondrial genome. The gene order differs from that in trypanosomatids, as does the organization of putative guide RNA genes; guide RNA-like molecules are transcribed from tandemly repeated 1-kb sequences organized in 200- and 170-kb molecules instead of minicircles. The presence of pan-editing in this lineage is consistent with an ancient evolutionary origin of this process.

RNA editing and mitochondrial genomic organization in the cryptobiid kinetoplastid protozoan Trypanoplasma borreli

The bodonids and cryptobiids represent an early diverged sister group to the trypanosomatids among the kinetoplastid protozoa. The trypanosome type of uridine insertion-deletion RNA editing was found to occur in the cryptobiid fish parasite Trypanoplasma borreli. A pan-edited ribosomal protein, S12, and a novel 3'- and 5'-edited cytochrome b, in addition to an unedited cytochrome oxidase III gene and an apparently unedited 12S rRNA gene, were found in a 6-kb fragment of the 80- to 90-kb mitochondrial genome. The gene order differs from that in trypanosomatids, as does the organization of putative guide RNA genes; guide RNA-like molecules are transcribed from tandemly repeated 1-kb sequences organized in 200- and 170-kb molecules instead of minicircles. The presence of pan-editing in this lineage is consistent with an ancient evolutionary origin of this process.

Evolution of RNA editing in kinetoplastid protozoa

The editing of RNA in trypanosomatid mitochondria involves the insertion and occasional deletion of uridine residues within coding regions of maxicircle messenger RNA transcripts. The extent to which the transcripts of homologous genes undergo editing differs in different species. In some, entire genes are edited (pan-editing), whereas in others, editing is limited to the 5' termini of editing domains (5' editing). Here we investigate which type of editing is ancestral and which is derived, by analysing RNA editing in the different lineages, using a kinetoplastid phylogeny reconstructed from nuclear small subunit ribosomal RNA sequences. We conclude that the ancestral cryptogenes were pan-edited, and we hypothesize that the 5'-edited homologues were generated by several independent events from partially edited RNAs, in which case editing may be a more primitive mechanism than previously thought.

Organization of mini-exon and 5S rRNA genes in the kinetoplastid Trypanoplasma borreli

Mini-exon gene repeats from Trypanoplasma borreli, which belongs to the Cryptobiidae family of the Bodonina suborder of the Kinetoplastida, were isolated by PCR amplification and cloning. The presence of kinetoplastid-like mini-exon genes in T. borreli is consistent with the taxonomic status of this organism as a kinetoplastid protozoan. Two families of repeats were found: 597 nt (T1) and 794 nt (T2), each of which encodes an approximately 95-nt medRNA transcript. The T1 repeats also contain a complete 5S rRNA gene on the complementary strand. The T2 repeats contain a defective copy of a 5S gene, in which the 5' portion is absent. The intergenic regions between the 5'-ends of the mini-exon genes and the 5S rRNA genes in the T1 and T2 repeats are highly diverged. All or most mini-exon genes and 5S genes are located within either the T1 or the T2 repeats. The T1 repeats were localized to a megabase-size chromosome, while the T2 repeats were localized within at least 4 large chromosomes.