The molecular evolution of trypanosomes

The Glycosylphosphatidylinositol Anchor: A Linchpin for Cell Surface Versatility of Trypanosomatids

The use of glycosylphosphatidylinositol (GPI) to anchor proteins to the cell surface is widespread among eukaryotes. The GPI-anchor is covalently attached to the C-terminus of a protein and mediates the protein’s attachment to the outer leaflet of the lipid bilayer. GPI-anchored proteins have a wide range of functions, including acting as receptors, transporters, and adhesion molecules. In unicellular eukaryotic parasites, abundantly expressed GPI-anchored proteins are major virulence factors, which support infection and survival within distinct host environments. While, for example, the variant surface glycoprotein (VSG) is the major component of the cell surface of the bloodstream form of African trypanosomes, procyclin is the most abundant protein of the procyclic form which is found in the invertebrate host, the tsetse fly vector. Trypanosoma cruzi, on the other hand, expresses a variety of GPI-anchored molecules on their cell surface, such as mucins, that interact with their hosts. The latter is also true for Leishmania, which use GPI anchors to display, amongst others, lipophosphoglycans on their surface. Clearly, GPI-anchoring is a common feature in trypanosomatids and the fact that it has been maintained throughout eukaryote evolution indicates its adaptive value. Here, we explore and discuss GPI anchors as universal evolutionary building blocks that support the great variety of surface molecules of trypanosomatids.

Diversity and Epidemiology of Bat Trypanosomes: A One Health Perspective

Bats (order Chiroptera) have been increasingly recognised as important reservoir hosts for human and animal pathogens worldwide. In this context, molecular and microscopy-based investigations to date have revealed remarkably high diversity of Trypanosoma spp. harboured by bats, including species of recognised medical and veterinary importance such as Trypanosoma cruzi and Trypanosoma evansi (aetiological agents of Chagas disease and Surra, respectively). This review synthesises current knowledge on the diversity, taxonomy, evolution and epidemiology of bat trypanosomes based on both molecular studies and morphological records. In addition, we use a One Health approach to discuss the significance of bats as reservoirs (and putative vectors) of T. cruzi, with a focus on the complex associations between intra-specific genetic diversity and eco-epidemiology of T. cruzi in sylvatic and domestic ecosystems. This article also highlights current knowledge gaps on the biological implications of trypanosome co-infections in a single host, as well as the prevalence, vectors, life-cycle, host-range and clinical impact of most bat trypanosomes recorded to date. Continuous research efforts involving molecular surveillance of bat trypanosomes are required for improved disease prevention and control, mitigation of biosecurity risks and potential spill-over events, ultimately ensuring the health of humans, domestic animals and wildlife globally.

18S rRNA gene sequence-structure phylogeny of the Trypanosomatida (Kinetoplastea, Euglenozoa) with special reference to Trypanosoma

Parasites of the order Trypanosomatida are known due to their medical relevance. Despite the progress made in the past decades on understanding the evolution of this group of organisms, there are still many open questions that require robust phylogenetic markers to increase the resolution of trees. Using two known 18S rRNA gene template structures (from Trypanosoma cruzi Chagas, 1909 and Trypanosoma brucei Plimmer and Bradford, 1899), individual 18S rRNA gene secondary structures were predicted by homology modeling. Sequences and their secondary structures, automatically encoded by a 12-letter alphabet (each nucleotide with its three structural states, paired left, paired right, unpaired), were simultaneously aligned. Sequence-structure trees were generated by neighbor joining and/or maximum likelihood. The reconstructed trees allowed us to discuss not only the big picture of trypanosomatid phylogeny but also a comprehensive sampling of trypanosomes evaluated in the context of trypanosomatid diversity. The robust support (bootstrap > 75) for well-known clades and critical branches suggests that the simultaneous use of 18S rRNA sequence and secondary structure data can reconstruct robust phylogenetic trees and can be used by the trypanosomatid research community for future analysis.

Phylogenetics, patterns of genetic variation and population dynamics of Trypanosoma terrestris support both coevolution and ecological host-fitting as processes driving trypanosome evolution

BACKGROUND

A considerable amount of evidence has favored ecological host-fitting, rather than coevolution, as the main mechanism responsible for trypanosome divergence. Nevertheless, beyond the study of human pathogenic trypanosomes, the genetic basis of host specificity among trypanosomes isolated from forest-inhabiting hosts remains largely unknown.

METHODS

To test possible scenarios on ecological host-fitting and coevolution, we combined a host capture recapture strategy with parasite genetic data and studied the genetic variation, population dynamics and phylogenetic relationships of Trypanosoma terrestris, a recently described trypanosome species isolated from lowland tapirs in the Brazilian Pantanal and Atlantic Forest biomes.

RESULTS

We made inferences of T. terrestris population structure at three possible sources of genetic variation: geography, tapir hosts and 'putative' vectors. We found evidence of a bottleneck affecting the contemporary patterns of parasite genetic structure, resulting in little genetic diversity and no evidence of genetic structure among hosts or biomes. Despite this, a strongly divergent haplotype was recorded at a microgeographical scale in the landscape of Nhecolândia in the Pantanal. However, although tapirs are promoting the dispersion of the parasites through the landscape, neither geographical barriers nor tapir hosts were involved in the isolation of this haplotype. Taken together, these findings suggest that either host-switching promoted by putative vectors or declining tapir population densities are influencing the current parasite population dynamics and genetic structure. Similarly, phylogenetic analyses revealed that T. terrestris is strongly linked to the evolutionary history of its perissodactyl hosts, suggesting a coevolving scenario between Perissodactyla and their trypanosomes. Additionally, T. terrestris and T. grayi are closely related, further indicating that host-switching is a common feature promoting trypanosome evolution.

CONCLUSIONS

This study provides two lines of evidence, both micro- and macroevolutionary, suggesting that both host-switching by ecological fitting and coevolution are two important and non-mutually-exclusive processes driving the evolution of trypanosomes. In line with other parasite systems, our results support that even in the face of host specialization and coevolution, host-switching may be common and is an important determinant of parasite diversification.

Basalin is an evolutionarily unconstrained protein revealed via a conserved role in flagellum basal plate function

Most motile flagella have an axoneme that contains nine outer microtubule doublets and a central pair (CP) of microtubules. The CP coordinates the flagellar beat and defects in CP projections are associated with motility defects and human disease. The CP nucleate near a ‘basal plate’ at the distal end of the transition zone (TZ). Here, we show that the trypanosome TZ protein ‘basalin’ is essential for building the basal plate, and its loss is associated with CP nucleation defects, inefficient recruitment of CP assembly factors to the TZ, and flagellum paralysis. Guided by synteny, we identified a highly divergent basalin ortholog in the related Leishmania species. Basalins are predicted to be highly unstructured, suggesting they may act as ‘hubs’ facilitating many protein-protein interactions. This raises the general concept that proteins involved in cytoskeletal functions and appearing organism-specific, may have highly divergent and cryptic orthologs in other species.

Molecular characterization and phylogenetic analysis of Trypanosoma evansi from Northern India based on 18S ribosomal gene

Six Trypanosoma evansi isolates were collected from ponies (PH1 and PK6), camel (CB2), donkeys (DJ3 and DH4) and cattle (CK5) from different States of Northern India (Haryana, Rajasthan, Uttar Pradesh and Gujarat) for molecular characterization based on 18S rRNA gene. The 18S rRNA gene (2251 bp) of different isolates was amplified, cloned and custom sequenced separately. Based on sequence and phylogenetic analysis of all six isolates, collected from different hosts as well as geographical areas, were having high identity among Indian T. evansi strains (99.7%) and with other strains of T. evansi (99.2%) distributed worldwide. There is less genetic diversity among different salivarian strains of T. evansi except few nucleotide changes at significant locations in one Indian isolate of camel origin (CB2). All Indian T. evansi isolates were grouped in salivarian clade with high bootstrap values and remained far away from stercorarian clade having 88-90% nucleotide identity. The study will be helpful in understanding the evolutionary relationship, molecular epidemiology and variation in disease pathogenesis among different T. evansi strains. Further, more studies are required on large number of isolates collected from diverse host and geographical areas to reaffirm the present finding.

Tsetse fly evolution, genetics and the trypanosomiases - A review

This reviews work published since 2007. Relative efforts devoted to the agents of African trypanosomiasis and their tsetse fly vectors are given by the numbers of PubMed accessions. In the last 10 years PubMed citations number 3457 for Trypanosoma brucei and 769 for Glossina. The development of simple sequence repeats and single nucleotide polymorphisms afford much higher resolution of Glossina and Trypanosoma population structures than heretofore. Even greater resolution is offered by partial and whole genome sequencing. Reproduction in T. brucei sensu lato is principally clonal although genetic recombination in tsetse salivary glands has been demonstrated in T. b. brucei and T. b. rhodesiense but not in T. b. gambiense. In the past decade most genetic attention was given to the chief human African trypanosomiasis vectors in subgenus Nemorhina e.g., Glossina f. fuscipes, G. p. palpalis, and G. p. gambiense. The chief interest in Nemorhina population genetics seemed to be finding vector populations sufficiently isolated to enable efficient and long-lasting suppression. To this end estimates were made of gene flow, derived from F_ST and its analogues, and Ne, the size of a hypothetical population equivalent to that under study. Genetic drift was greater, gene flow and Ne typically lesser in savannah inhabiting tsetse (subgenus Glossina) than in riverine forms (Nemorhina). Population stabilities were examined by sequential sampling and genotypic analysis of nuclear and mitochondrial genomes in both groups and found to be stable. Gene frequencies estimated in sequential samplings differed by drift and allowed estimates of effective population numbers that were greater for Nemorhina spp than Glossina spp. Prospects are examined of genetic methods of vector control. The tsetse long generation time (c. 50 d) is a major contraindication to any suggested genetic method of tsetse population manipulation. Ecological and modelling research convincingly show that conventional methods of targeted insecticide applications and traps/targets can achieve cost-effective reduction in tsetse densities.

Bat trypanosomes from Tapajós-Arapiuns Extractive Reserve in Brazilian Amazon

Trypanosoma comprises flagellates able to infect several mammalian species and is transmitted by several groups of invertebrates. The order Chiroptera can be infected by the subgenera Herpetosoma, Schizotrypanum, Megatrypanum and Trypanozoon. In this study, we described the diversity of bat trypanosomes and inferred phylogenetic relationships among the trypanosomes from bats caught in Tapajós-Arapiuns Extractive Reserve (Resex) in Pará state. Trypanosomes from bats were isolated by means of hemoculture, and the molecular phylogeny was based on the trypanosome barcode (SSUrDNA V7V8 variable region). A total of 111 bats were caught in the area, belonging to three families (Emballonuridae, Molossidae and Phyllostomidae) and 12 species. The bat trypanosome prevalence, as evaluated through hemoculture, was 9% all positive cultures were cryopreserve (100% of isolation success). Phylogenetic trees grouped nine isolates in T. cruzi marinkellei branch and only one in T. dionisii branch. Studies on bat trypanosome diversity are important for identifying pathogenic species and for generating support for control measures, especially in such areas where humans inhabit the forest with close contact with bat species. In addition, this is the first study in Resex Tapajós-Arapiuns extractive reserve and further studies should be conducted to elucidate the role of these parasites as environmental degradation biomarkers.

An Alternative Strategy for Trypanosome Survival in the Mammalian Bloodstream Revealed through Genome and Transcriptome Analysis of the Ubiquitous Bovine Parasite Trypanosoma (Megatrypanum) theileri

There are hundreds of Trypanosoma species that live in the blood and tissue spaces of their vertebrate hosts. The vast majority of these do not have the ornate system of antigenic variation that has evolved in the small number of African trypanosome species, but can still maintain long-term infections in the face of the vertebrate adaptive immune system. Trypanosoma theileri is a typical example, has a restricted host range of cattle and other Bovinae, and is only occasionally reported to cause patent disease although no systematic survey of the effect of infection on agricultural productivity has been performed. Here, a detailed genome sequence and a transcriptome analysis of gene expression in bloodstream form T. theileri have been performed. Analysis of the genome sequence and expression showed that T. theileri has a typical kinetoplastid genome structure and allowed a prediction that it is capable of meiotic exchange, gene silencing via RNA interference and, potentially, density-dependent growth control. In particular, the transcriptome analysis has allowed a comparison of two distinct trypanosome cell surfaces, T. brucei and T. theileri, that have each evolved to enable the maintenance of a long-term extracellular infection in cattle. The T. theileri cell surface can be modeled to contain a mixture of proteins encoded by four novel large and divergent gene families and by members of a major surface protease gene family. This surface composition is distinct from the uniform variant surface glycoprotein coat on African trypanosomes providing an insight into a second mechanism used by trypanosome species that proliferate in an extracellular milieu in vertebrate hosts to avoid the adaptive immune response.

Small subunit ribosomal metabarcoding reveals extraordinary trypanosomatid diversity in Brazilian bats

BACKGROUND

Bats are a highly successful, globally dispersed order of mammals that occupy a wide array of ecological niches. They are also intensely parasitized and implicated in multiple viral, bacterial and parasitic zoonoses. Trypanosomes are thought to be especially abundant and diverse in bats. In this study, we used 18S ribosomal RNA metabarcoding to probe bat trypanosome diversity in unprecedented detail.

METHODOLOGY/PRINCIPAL FINDINGS

Total DNA was extracted from the blood of 90 bat individuals (17 species) captured along Atlantic Forest fragments of Espírito Santo state, southeast Brazil. 18S ribosomal RNA was amplified by standard and/or nested PCR, then deep sequenced to recover and identify Operational Taxonomic Units (OTUs) for phylogenetic analysis. Blood samples from 34 bat individuals (13 species) tested positive for infection by 18S rRNA amplification. Amplicon sequences clustered to 14 OTUs, of which five were identified as Trypanosoma cruzi I, T. cruzi III/V, Trypanosoma cruzi marinkellei, Trypanosoma rangeli, and Trypanosoma dionisii, and seven were identified as novel genotypes monophyletic to basal T. cruzi clade types of the New World. Another OTU was identified as a trypanosome like those found in reptiles. Surprisingly, the remaining OTU was identified as Bodo saltans-closest non-parasitic relative of the trypanosomatid order. While three blood samples featured just one OTU (T. dionisii), all others resolved as mixed infections of up to eight OTUs.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates the utility of next-generation barcoding methods to screen parasite diversity in mammalian reservoir hosts. We exposed high rates of local bat parasitism by multiple trypanosome species, some known to cause fatal human disease, others non-pathogenic, novel or yet little understood. Our results highlight bats as a long-standing nexus among host-parasite interactions of multiple niches, sustained in part by opportunistic and incidental infections of consequence to evolutionary theory as much as to public health.

Continental Drift and Speciation of the Cryptococcus neoformans and Cryptococcus gattii Species Complexes

Genomic analysis has placed the origins of two human-pathogenic fungi, the Cryptococcus gattii species complex and the Cryptococcus neoformans species complex, in South America and Africa, respectively. Molecular clock calculations suggest that the two species separated ~80 to 100 million years ago. This time closely approximates the breakup of the supercontinent Pangea, which gave rise to South America and Africa. On the basis of the geographic distribution of these two species complexes and the coincidence of the evolutionary divergence and Pangea breakup times, we propose that a spatial separation caused by continental drift resulted in the emergence of the C. gattii and C. neoformans species complexes from a Pangean ancestor. We note that, despite the spatial and temporal separation that occurred approximately 100 million years ago, these two species complexes are morphologically similar, share virulence factors, and cause very similar diseases. Continuation of these phenotypic characteristics despite ancient separation suggests the maintenance of similar selection pressures throughout geologic ages.

A Receptor's Tale: An Eon in the Life of a Trypanosome Receptor

African trypanosomes have complex life cycles comprising at least ten developmental forms, variously adapted to different niches in their tsetse fly vector and their mammalian hosts. Unlike many other protozoan pathogens, they are always extracellular and have evolved intricate surface coats that allow them to obtain nutrients while also protecting them from the immune defenses of either insects or mammals. The acquisition of macromolecular nutrients requires receptors that function within the context of these surface coats. The best understood of these is the haptoglobin-hemoglobin receptor (HpHbR) of Trypanosoma brucei, which is used by the mammalian bloodstream form of the parasite, allowing heme acquisition. However, in some primates it also provides an uptake route for trypanolytic factor-1, a mediator of innate immunity against trypanosome infection. Recent studies have shown that during the evolution of African trypanosome species the receptor has diversified in function from a hemoglobin receptor predominantly expressed in the tsetse fly to a haptoglobin-hemoglobin receptor predominantly expressed in the mammalian bloodstream. Structural and functional studies of homologous receptors from different trypanosome species have allowed us to propose an evolutionary history for how one receptor has adapted to different roles in different trypanosome species. They also highlight the challenges that a receptor faces in operating on the complex trypanosome surface and show how these challenges can be met.

Diversity of bats trypanosomes in hydroeletric area of Belo Monte in Brazilian Amazonia

The Trypanosoma comprises flagellates able to infect many mammalian species and is transmitted by several groups of invertebrates. The order Chiroptera can be infected by the subgenera Herpetosoma, Schizotrypanum, Megatrypanum and Trypanozoon. In this study, we described the diversity of bats trypanosomes, inferring the phylogenetic relationships among the trypanosomes from bats caught Belo Monte Hydroeletric area (Brazilian Amazonia). Trypanosomes from bats were isolated by haemoculture, and the molecular phylogeny based on small subunit rDNA (SSU rDNA) and glycosomal-3-phosphate dehydrogenase (gGAPDH) gene sequences. Morphological characterization included light and scanning electron microscopy. A total of 157 bats were caught in the area belonging 6 Families (Emballonuridae, Furipteridae, Mormoopidae, Natalidae, Phyllostomidae and Vespertilionidae) and 34 species. The bat trypanosome prevalence, as evaluated through haemoculture, was 5,7%. Phylogenetic trees grouped the isolates in T. cruzi branch (TCI and TCbat lineage), T. cruzi marinkellei and Trypanosoma wauwau from Pteronotus parnellii. This is the first isolate from T. wauwau in Para state. The occurrence of T. cruzi in the ​​ Belo Monte Hydroeletric area (UHE Belo Monte) in Amazon/Brazil attentive to the risk of migration human population required for the works of the dam and new cities that grow in the vicinity of these businesses, but it is a zoonosis already known to the Amazon region, and the presence of unclassified Trypanosoma species, attend to the large parasitic biodiversity still unknown.

Phylogenetic analysis of the Trypanosoma genus based on the heat-shock protein 70 gene

Trypanosome evolution was so far essentially studied on the basis of phylogenetic analyses of small subunit ribosomal RNA (SSU-rRNA) and glycosomal glyceraldehyde-3-phosphate dehydrogenase (gGAPDH) genes. We used for the first time the 70kDa heat-shock protein gene (hsp70) to investigate the phylogenetic relationships among 11 Trypanosoma species on the basis of 1380 nucleotides from 76 sequences corresponding to 65 strains. We also constructed a phylogeny based on combined datasets of SSU-rDNA, gGAPDH and hsp70 sequences. The obtained clusters can be correlated with the sections and subgenus classifications of mammal-infecting trypanosomes except for Trypanosoma theileri and Trypanosoma rangeli. Our analysis supports the classification of Trypanosoma species into clades rather than in sections and subgenera, some of which being polyphyletic. Nine clades were recognized: Trypanosoma carassi, Trypanosoma congolense, Trypanosoma cruzi, Trypanosoma grayi, Trypanosoma lewisi, T. rangeli, T. theileri, Trypanosoma vivax and Trypanozoon. These results are consistent with existing knowledge of the genus' phylogeny. Within the T. cruzi clade, three groups of T. cruzi discrete typing units could be clearly distinguished, corresponding to TcI, TcIII, and TcII+V+VI, while support for TcIV was lacking. Phylogenetic analyses based on hsp70 demonstrated that this molecular marker can be applied for discriminating most of the Trypanosoma species and clades.

Phylogenomic reconstruction supports supercontinent origins for Leishmania

Leishmania, a genus of parasites transmitted to human hosts and mammalian/reptilian reservoirs by an insect vector, is the causative agent of the human disease complex leishmaniasis. The evolutionary relationships within the genus Leishmania and its origins are the source of ongoing debate, reflected in conflicting phylogenetic and biogeographic reconstructions. This study employs a recently described bioinformatics method, SISRS, to identify over 200,000 informative sites across the genome from newly sequenced and publicly available Leishmania data. This dataset is used to reconstruct the evolutionary relationships of this genus. Additionally, we constructed a large multi-gene dataset, using it to reconstruct the phylogeny and estimate divergence dates for species. We conclude that the genus Leishmania evolved at least 90-100 million years ago, supporting a modified version of the Multiple Origins hypothesis that we call the Supercontinent hypothesis. According to this scenario, separate Leishmania clades emerged prior to, and during, the breakup of Gondwana. Additionally, we confirm that reptile-infecting Leishmania are derived from mammalian forms and that the species that infect porcupines and sloths form a clade long separated from other species. Finally, we firmly place the guinea-pig infecting species, Leishmaniaenriettii, the globally dispersed Leishmaniasiamensis, and the newly identified Australian species from a kangaroo, as sibling species whose distribution arises from the ancient connection between Australia, Antarctica, and South America.

An overview on the ecology of Triatominae (Hemiptera:Reduviidae)

Chagas disease, the American trypanosomiasis, is an important neglected tropical illness caused by the flagellate protozoan Trypanosoma cruzi (Kinetoplastida, Trypanosomatidae) and transmitted by insects of the subfamily Triatominae (Hemiptera: Reduviidae). Here we provide an overview on the current knowledge about Triatominae ecology, its association with human, T. cruzi infection and the immediate consequences of habitat fragmentation. We also discuss the geographic distribution of the species and the importance of predicting their distributions to control programs.

Molecular characterization and classification of Trypanosoma spp. Venezuelan isolates based on microsatellite markers and kinetoplast maxicircle genes

BACKGROUND

Livestock trypanosomoses, caused by three species of the Trypanozoon subgenus, Trypanosoma brucei brucei, T. evansi and T. equiperdum is widely distributed throughout the world and constitutes an important limitation for the production of animal protein. T. evansi and T. equiperdum are morphologically indistinguishable parasites that evolved from a common ancestor but acquired important biological differences, including host range, mode of transmission, distribution, clinical symptoms and pathogenicity. At a molecular level, T. evansi is characterized by the complete loss of the maxicircles of the kinetoplastic DNA, while T. equiperdum has retained maxicircle fragments similar to those present in T. brucei. T. evansi causes the disease known as Surra, Derrengadera or "mal de cadeiras", while T. equiperdum is the etiological agent of dourine or "mal du coit", characterized by venereal transmission and white patches in the genitalia.

METHODS

Nine Venezuelan Trypanosoma spp. isolates, from horse, donkey or capybara were genotyped and classified using microsatellite analyses and maxicircle genes. The variables from the microsatellite data and the Procyclin PE repeats matrices were combined using the Hill-Smith method and compared to a group of T. evansi, T. equiperdum and T. brucei reference strains from South America, Asia and Africa using Coinertia analysis. Four maxicircle genes (cytb, cox1, a6 and nd8) were amplified by PCRfrom TeAp-N/D1 and TeGu-N/D1, the two Venezuelan isolates that grouped with the T. equiperdum STIB841/OVI strain. These maxicircle sequences were analyzed by nucleotide BLAST and aligned toorthologous genes from the Trypanozoon subgenus by MUSCLE tools. Phylogenetic trees were constructed using Maximum Parsimony (MP) and Maximum Likelihood (ML) with the MEGA5.1® software.

RESULTS

We characterized microsatellite markers and Procyclin PE repeats of nine Venezuelan Trypanosoma spp. isolates with various degrees of virulence in a mouse model, and compared them to a panel of T. evansi and T. equiperdum reference strains. Coinertia analysis of the combined repeats and previously reported T. brucei brucei microsatellite genotypes revealed three distinct groups. Seven of the Venezuelan isolates grouped with globally distributed T. evansi strains, while TeAp-N/D1 and TeGu-N/D1 strains clustered in a separate group with the T. equiperdum STIB841/OVI strain isolated in South Africa. A third group included T. brucei brucei, two strains previously classified as T. evansi (GX and TC) and one as T. equiperdum (BoTat-1.1). Four maxicircle genes, Cytochrome b, Cythocrome Oxidase subunit 1, ATP synthase subunit 6 and NADH dehydrogenase subunit 8, were identified in the two Venezuelan strains clustering with the T. equiperdum STIB841/OVI strain. Phylogenetic analysis of the cox1 gene sequences further separated these two Venezuelan T. equiperdum strains: TeAp-N/D1 grouped with T. equiperdum strain STIB818 and T. brucei brucei, and TeGu-N/D1 with the T. equiperdum STIB841/OVI strain.

CONCLUSION

Based on the Coinertia analysis and maxicircle gene sequence phylogeny, TeAp-N/D1 and TeGu-N/D1 constitute the first confirmed T. equiperdum strains described from Latin America.

The Human-Animal Interface

The human-animal interface is as ancient as the first bipedal steps taken by humans. Born with the human species, it has grown and expanded with the human species' prehistoric and historical development to reach the unprecedented scope of current times. Several facets define the human-animal interface, guiding the scope and range of human interactions with animal species. These facets have not ceased to evolve and expand since their emergence, all the more favoring disease emergence. Placing the human-animal interface in its historical perspective allows us to realize its versatile and dynamic nature. Changes in the scope and range of domestication, agriculture, urbanization, colonization, trade, and industrialization have been accompanied by evolving risks for cross-species transmission of pathogens. Because these risks are unlikely to decrease, improving our technologies to identify and monitor pathogenic threats lurking at the human-animal interface should be a priority.

Morphological and molecular characterization and phylogenetic relationships of a new species of trypanosome in Tapirus terrestris (lowland tapir), Trypanosoma terrestris sp. nov., from Atlantic Rainforest of southeastern Brazil

Background

The Lowland tapir (Tapirus terrestris) is the largest Brazilian mammal and despite being distributed in various Brazilian biomes, it is seriously endangered in the Atlantic Rainforest. These hosts were never evaluated for the presence of Trypanosoma parasites.

Methods

The Lowland tapirs were captured in the Brazilian southeastern Atlantic Rainforest, Espírito Santo state. Trypanosomes were isolated by hemoculture, and the molecular phylogeny based on small subunit rDNA (SSU rDNA) and glycosomal-3-phosphate dehydrogenase (gGAPDH) gene sequences and the ultrastructural features seen via light microscopy and scanning and transmission electron microscopy are described.

Results

Phylogenetic trees using combined SSU rDNA and gGAPDH data sets clustered the trypanosomes of Lowland tapirs, which were highly divergent from other trypanosome species. The phylogenetic position and morphological discontinuities, mainly in epimastigote culture forms, made it possible to classify the trypanosomes from Lowland tapirs as a separate species.

Conclusions

The isolated trypanosomes from Tapirus terrestris are a new species, Trypanosoma terrestris sp. n., and were positioned in a new Trypanosoma clade, named T. terrestris clade.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-6-349) contains supplementary material, which is available to authorized users.

The improbable transmission of Trypanosoma cruzi to human: the missing link in the dynamics and control of Chagas disease

Chagas disease has a major impact on human health in Latin America and is becoming of global concern due to international migrations. Trypanosoma cruzi, the etiological agent of the disease, is one of the rare human parasites transmitted by the feces of its vector, as it is unable to reach the salivary gland of the insect. This stercorarian transmission is notoriously poorly understood, despite its crucial role in the ecology and evolution of the pathogen and the disease. The objective of this study was to quantify the probability of T. cruzi vectorial transmission to humans, and to use such an estimate to predict human prevalence from entomological data. We developed several models of T. cruzi transmission to estimate the probability of transmission from vector to host. Using datasets from the literature, we estimated the probability of transmission per contact with an infected triatomine to be 5.8 × 10(-4) (95%CI: [2.6 ; 11.0] × 10(-4)). This estimate was consistent across triatomine species, robust to variations in other parameters, and corresponded to 900-4,000 contacts per case. Our models subsequently allowed predicting human prevalence from vector abundance and infection rate in 7/10 independent datasets covering various triatomine species and epidemiological situations. This low probability of T. cruzi transmission reflected well the complex and unlikely mechanism of transmission via insect feces, and allowed predicting human prevalence from basic entomological data. Although a proof of principle study would now be valuable to validate our models' predictive ability in an even broader range of entomological and ecological settings, our quantitative estimate could allow switching the evaluation of disease risk and vector control program from purely entomological indexes to parasitological measures, as commonly done for other major vector borne diseases. This might lead to different quantitative perspectives as these indexes are well known not to be proportional one to another.

The importance of understanding the human-animal interface : from early hominins to global citizens

The complex relationships between the human and animal species have never ceased to evolve since the emergence of the human species and have resulted in a human-animal interface that has promoted the cross-species transmission, emergence and eventual evolution of a plethora of infectious pathogens. Remarkably, most of the characteristics of the human-animal interface-as we know it today-have been established long before the end of our species pre-historical development took place, to be relentlessly shaped throughout the history of our species. More recently, changes affecting the modern human population worldwide as well as their dramatic impact on the global environment have taken domestication, agriculture, urbanization, industrialization, and colonization to unprecedented levels. This has created a unique global multi-faceted human-animal interface, associated with a major epidemiological transition that is accompanied by an unexpected rise of new and emerging infectious diseases. Importantly, these developments are largely paralleled by medical, technological, and scientific progress, continuously spurred by our never-ending combat against pathogens. The human-animal interface has most likely contributed significantly to the evolutionary shaping and historical development of our species. Investment in a better understanding of this human-animal interface will offer humankind a future head-start in the never-ending battle against infectious diseases.

The evolution of Trypanosoma cruzi: the 'bat seeding' hypothesis

Recent discussions on the evolution of Trypanosoma cruzi have been dominated by the southern super-continent hypothesis, whereby T. cruzi and related parasites evolved in isolation in the mammals of South America, Antarctica and Australia. Here, we consider recent molecular evidence suggesting that T. cruzi evolved from within a broader clade of bat trypanosomes, and that bat trypanosomes have successfully made the switch into other mammalian hosts in both the New and Old Worlds. Accordingly, we propose an alternative hypothesis--the bat seeding hypothesis--whereby lineages of bat trypanosomes have switched into terrestrial mammals, thereby seeding the terrestrial lineages within the clade. One key implication of this finding is that T. cruzi may have evolved considerably more recently than previously envisaged.

Molecular survey of rodent-borne Trypanosoma in Niger with special emphasis on T. lewisi imported by invasive black rats

Invading rodent species can harbor parasites with potential transmission to native rodents and/or humans. To investigate trypanosomes prevalence in rodents, the spleen of 76 rodents from Niger identified by their karyotype was used as a DNA source for Trypanosoma detection using a newly developed qPCR assay. Of the invasive black rat, Rattus rattus, 71% (10/14) were PCR positive as well as 6% (4/62) of native African rodents. Sequences of ~400bp of the SSU rDNA gene identified phylogenetically close Trypanosoma lineages. Trypanosoma lewisi was present in all positive black rats and the sequences displayed 100% similarity with T. lewisi-infected humans in Senegal. T. lewisi was also detected in one Acomys johannis, suggesting a possible transmission to native species. In addition to improved knowledge of Trypanosoma diversity in rodents, our data underscore the introduction of the potentially pathogenic T. lewisi kinetoplastid through the human-mediated invasion of black rats all over West Africa.

Increased expression of recombinant human tissue plasminogen activator in Leishmania tarentolae

Recombinant tissue plasminogen activator (rt-PA) is one of the most important thrombolytic agents for treating cardiovascular obstructions such as stroke. Glycoprotein rt-PA is a serine protease, consisting of 527 amino acids of which 35 are cysteine residues. A variety of recombinant protein expression systems have been developed for heterologous gene expression in prokaryotic and eukaryotic hosts. In recent years, Leishmania tarentolae has been considered because of its safety aspects and special attributes in expression of complex proteins. In this study, two expression cassettes, each one including two copies of t-PA cDNA, were used for integration into the L. tarentolae genome by electroporation. Transformed clones were selected in the presence of appropriate antibiotics. Expression of active rt-PA was confirmed by Western blot and Zymography tests. Real-time PCR analysis was applied to investigate the presence of multiple t-PA gene copies in the parasite genome. Correlation of t-PA gene dosage and production rate was confirmed with real-time PCR. It was shown that the expression level of rt-PA in L. tarentolae is at least 480 IU/mL of culture media. This concentration of rt-PA is seven times higher than what was reported in previous studies in L. tarentolae and some other eukaryotic systems.

The Leishmania amazonensis TRF (TTAGGG repeat-binding factor) homologue binds and co-localizes with telomeres

BACKGROUND

Telomeres are specialized structures at the end of chromosomes essential for maintaining genome stability and cell viability. The importance of telomeric proteins for telomere maintenance has increased our interest in the identification of homologues within the genus Leishmania. The mammalian TRF1 and TRF2 proteins, for example, bind double-stranded telomeres via a Myb-like DNA-binding domain and are involved with telomere length regulation and chromosome end protection. In addition, TRF2 can modulate the activity of several enzymes and influence the conformation of telomeric DNA. In this work, we identified and characterized a Leishmania protein (LaTRF) homologous to both mammalian TRF1 and TRF2.

RESULTS

LaTRF was cloned using a PCR-based strategy. ClustalW and bl2seq sequence analysis showed that LaTRF shared sequence identity with the Trypanosoma brucei TRF (TbTRF) protein and had the same degree of sequence similarities with the dimerization (TRFH) and the canonical DNA-binding Myb-like domains of both mammalian TRFs. LaTRF was predicted to be an 82.5 kDa protein, indicating that it is double the size of the trypanosome TRF homologues. Western blot and indirect immunofluorescence combined with fluorescence in situ hybridization showed that LaTRF, similarly to hTRF2, is a nuclear protein that also associates with parasite telomeres. Native and full length LaTRF and a mutant bearing the putative Myb-like domain expressed in bacteria bound double-stranded telomeric DNA in vitro. Chromatin immunoprecipitation showed that LaTRF interacted specifically with telomeres in vivo.

CONCLUSION

The nuclear localization of LaTRF, its association and co-localization with parasite telomeres and its high identity with TbTRF protein, support the hypothesis that LaTRF is a Leishmania telomeric protein.

Herpetomonas trimorpha sp. nov. (Trypanosomatidae, Kinetoplastida), a parasite of the biting midge Culicoides truncorum (Ceratopogonidae, Diptera)

Monoxenous trypanosomatid Herpetomonas trimorpha sp. nov. was isolated from the digestive tract of the biting midge Culicoides truncorum (Ceratopogonidae, Diptera). This species forms three distinct morphotypes in culture: the microflagellate promastigote, the small promastigote and the long promastigote. The last form is unique for the newly described species. Phylogenetic analyses of SSU rRNA and glycosomal glyceraldehyde phosphate dehydrogenase genes showed that H. trimorpha sp. nov. is the closest relative of Herpetomonas ztiplika, another monoxenous trypanosomatid isolated from biting midges. However, morphological and randomly amplified polymorphic DNA analyses confirmed that H. trimorpha sp. nov. is distinct from H. ztiplika.

Genetic diversity of Trypanosoma evansi in buffalo based on internal transcribed spacer (ITS) regions

The nucleotide sequences of 18S rDNA and internal transcribed spacer (ITS) regions were used for studying the relationships of Trypanosoma evansi isolate from a buffalo. The sequences were analyzed and compared to 18S rDNA and the ITS regions of the other Trypanosoma spp. Maximum likelihood phylogenetic trees were constructed using Leishmania major as the outgroup. The tree of 18S rDNA indicated that T. evansi (buffalo B18) isolate was closely related to those of Taiwan and T. brucei stock. The ITS tree showed the genetic diversity among 32 clones of T. evansi (B18) within a single host. This data will be useful for epidemiological and dynamic studies for designing the rational control programs of the disease.

Trypanosoma evansi: molecular homogeneity as inferred by phenetical analysis of ribosomal internal transcribed spacers DNA of an eclectic parasite

The protozoan Trypanosoma evansi is described as presenting high morphological and genetic similarities among the isolates despite its biological heterogeneity and wide geographical distribution. PCR amplification of the internal transcribed spacers of the ribosomal gene in combination with the coding region of the 5.8S ribosomal subunit further submitted to restriction enzymes digestion were carried out in DNAs extracted from 41 T. evansi strains isolated from horses, dogs, coatis and capybaras from two distinct regions of the Brazilian Pantanal. We also used one T. evansi isolate from Africa, one from Asia and one isolate of T. b. brucei from Africa. Analysis of the RFLP profiles yielded a unique "riboprinting" that does not vary intraspecifically. These results provide insights on the ribosomal gene organization of T. evansi and showed that ITS analysis by RFLP show high genetic similarity of this locus among isolates of this protozoan parasite.

LaTBP1: A Leishmania amazonensis DNA-binding protein that associates in vivo with telomeres and GT-rich DNA using a Myb-like domain

Different species of Leishmania can cause a variety of medically important diseases, whose control and treatment are still health problems. Telomere binding proteins (TBPs) have potential as targets for anti-parasitic chemotherapy because of their importance for genome stability and cell viability. Here, we describe LaTBP1 a protein that has a Myb-like DNA-binding domain, a feature shared by most double-stranded telomeric proteins. Binding assays using full-length and truncated LaTBP1 combined with spectroscopy analysis were used to map the boundaries of the Myb-like domain near to the protein only tryptophan residue. The Myb-like domain of LaTBP1 contains a conserved hydrophobic cavity implicated in DNA-binding activity. A hypothetical model helped to visualize that it shares structural homology with domains of other Myb-containing proteins. Competition assays and chromatin immunoprecipitation confirmed the specificity of LaTBP1 for telomeric and GT-rich DNAs, suggesting that LaTBP1 is a new TBP.

Haemoparasites of common shrews (Sorex araneus) in Northwest England

The presence of haemoparasites belonging to the taxa Anaplasma, Bartonella and Trypanosoma was determined among 76 common shrews (Sorex araneus) from Northwest England. Anaplasma phagocytophilum DNA was recovered from the blood of 1 shrew (1.3%), with the amplified 16S rRNA sequence identical to one previously reported from a bank vole (Clethrionomys glareolus). Trypanosoma spp. DNA was detected in 9 shrews (11.8%), the amplified 18S rDNA fragments being indistinguishable from one another, and distinct from previously published data. This represents the first report of trypanosome infection in S. araneus and suggests they are susceptible to an uncharacterized Trypanosoma species. Blood from 11 shrews (14.5%) yielded Bartonella spp., with characterization of isolates using comparative sequence analysis of partial gltA and 16S-23S rRNA intergenic spacer regions revealing 2 different genotypes. Phylogenetic inference from alignment of partial gltA sequences found that both UK S. araneus types formed a well-supported cluster with Bartonella sp. isolated from S. araneus in Sweden. No significant effect of host age, sex, or year of collection was found on prevalence of Bartonella or trypanosome infections. The results of this survey demonstrate that common shrews in the UK are susceptible to haemoparasitic infections, at prevalences similar to those reported from sympatric rodents.

Identification of novel snRNA-specific Sm proteins that bind selectively to U2 and U4 snRNAs in Trypanosoma brucei

In eukaryotes the seven Sm core proteins bind to U1, U2, U4, and U5 snRNAs. In Trypanosoma brucei, Sm proteins have been implicated in binding both spliced leader (SL) and U snRNAs. In this study, we examined the function of these Sm proteins using RNAi silencing and protein purification. RNAi silencing of each of the seven Sm genes resulted in accumulation of SL RNA as well as reduction of several U snRNAs. Interestingly, U2 was unaffected by the loss of SmB, and both U2 and U4 snRNAs were unaffected by the loss of SmD3, suggesting that these snRNAs are not bound by the heptameric Sm complex that binds to U1, U5, and SL RNA. RNAi silencing and protein purification showed that U2 and U4 snRNAs were bound by a unique set of Sm proteins that we termed SSm (specific spliceosomal Sm proteins). This is the first study that identifies specific core Sm proteins that bind only to a subset of spliceosomal snRNAs.

The Marine Pathogenic Genotype of Spironucleus barkhanus from Farmed Salmonids Redescribed as Spironucleus salmonicida n. sp

There are two genotypes of the diplomonad Spironucleus barkhanus. Based on sequence data from the small subunit ribosomal RNA gene the conspecificity of these two genotypes has been questioned. Therefore, we have sampled Spironucleus from 27 fish, representing 14 populations, five species, and four genera. Partial nucleotide sequences from the three genes; small subunit ribosomal DNA, glutamate dehydrogenase 1 and alpha-tubulin were compared. The pathogenic isolates of S. barkhanus, which causes systemic spironucleosis in Atlantic salmon, Chinook salmon, and Arctic charr, all farmed in sea water, were genetically very different from the commensal isolate found in wild freshwater populations of Arctic charr and grayling. The genetic distances between the genotypes were of the same magnitude as those separating species of Giardia. Based on these genetic and ecological data, the pathogenic genotype from farmed salmonids is described as a new species, Spironucleus salmonicida n. sp. Scanning and transmission electron microscopy showed no specific morphological or ultrastructural features distinguishing S. salmonicida n. sp. from S. barkhanus. The present study clearly demonstrates the value of applying genetics in identification of Spironucleus species. Phylogenetic analyses that included the isolates of S. salmonicida n. sp. did not change the phylogenetic relationship within the genus Spironucleus.

Leptomonas costaricensis sp. n. (Kinetoplastea: Trypanosomatidae), a member of the novel phylogenetic group of insect trypanosomatids closely related to the genus Leishmania

A flagellate isolated from the intestinal tract of a reduviid bug Ricolla simillima (Heteroptera) in Costa Rica was found to represent a new trypanosomatid species by the phylogenetic analysis of small subunit ribosomal RNA (SSU rRNA), glyceraldehyde phosphate dehydrogenase (GAPDH) and large subunit of RNA polymerase II (RPOIILS) genes. The phylogenetic position of this trypanosomatid, together with its typical promastigote morphology and the host identity, allowed its classification as a species that belongs to the polyphyletic genus Leptomonas. Interestingly, the new species was revealed as a member of the novel phylogenetic clade representing the closest known relative of Leishmania. With the new species used as an outgroup to root the Leishmania RPOIILS phylogenetic tree, the lineage of the Neotropical species L. enriettii was found to branch off early, and was followed by a deep split between the Old World and the remaining New World species. This tree topology supports the hypothesis that the initial transition to dixenous parasitism in this group pre-dated the continental split and that afterwards the Neotropical and the Old World groups evolved largely independently.

Telomere structure and shortening in telomerase-deficient Trypanosoma brucei

Telomerase consists of a reverse transcriptase (TERT) and an RNA that contains a template for telomere-repeat extension. Telomerase is required to prevent telomere erosion and its activity or lack thereof is important for tumorigenesis and ageing. Telomerase has been identified in numerous organisms but it has not been studied in kinetoplastid protozoa. Trypanosoma brucei, the causative agent of African sleeping sickness, evades the host immune response by frequently changing its variant surface glycoprotein (VSG). The single expressed VSG is transcribed from one of ∼20 subtelomeric ‘Expression Sites’, but the role telomeres might play in regulating VSG transcription and switching is unknown. We identified and sequenced the T.brucei TERT gene. Deleting TERT resulted in progressive telomere shortening of 3–6 bp per generation. In other organisms, the rate of telomere shortening is proportional to the length of the terminal 3′ single-strand overhang. In T.brucei, G-overhangs were undetectable (<30 nt) by in-gel hybridization. The rate of telomere shortening therefore, agrees with the predicted shortening due to the end replication problem, and is consistent with our observation that G-overhangs are short. Trypanosomes whose telomere length can be manipulated provide a new tool to investigate the role of telomeres in antigenic variation.

Trypanosome telomeres are protected by a homologue of mammalian TRF2

Putative TTAGGG repeat-binding factor (TRF) homologues in the genomes of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major were identified. They have significant sequence similarity to higher eukaryotic TRFs in their C-terminal DNA-binding myb domains but only weak similarity in their N-terminal domains. T. brucei TRF (tbTRF) is essential and was shown to bind to duplex TTAGGG repeats. The RNA interference-mediated knockdown of tbTRF arrested bloodstream cells at G(2)/M and procyclic cells partly at S phase. Functionally, tbTRF resembles mammalian TRF2 more than TRF1, as knockdown diminished telomere single-stranded G-overhang signals. This suggests that tbTRF, like vertebrate TRF2, is essential for telomere end protection, and this also supports the hypothesis that TRF rather than Rap1 is the more ancient DNA-binding component of the telomere protein complex. Identification of the first T. brucei telomere DNA-binding protein and characterization of its function provide a new route to explore the roles of telomeres in pathogenesis of this organism. This work also establishes T. brucei as an attractive model for telomere biology.

Characterization of SSU and LSU rRNA genes of three Trypanosoma (Herpetosoma) grosi isolates maintained in Mongolian jirds

Trypanosoma (Herpetosoma) grosi, which naturally parasitizes Apodemus spp., can experimentally infect Mongolian jirds (Meriones unguiculatus). Three isolates from A. agrarius, A. peninsulae, and A. speciosus (named SESUJI, HANTO, and AKHA isolates, respectively) of different geographical origin (AKHA from Japan, and the others from Vladivostok), exhibited different durations of parasitaemia in laboratory jirds (2 weeks for HANTO, and 3 weeks for the others). To assess the genetic background of these T. grosi isolates, their small (SSU) and large subunit (LSU) ribosomal RNA genes (rDNA) were sequenced along with those of 2 other Herpetosoma species from squirrels. The SSU rDNA sequences of these 3 species along with available sequences of 3 other Herpetosoma trypanosomes (T. lewisi, T. musculi and T. microti) seemed to reflect well the phylogenetic relationship of their hosts. Three isolates of T. grosi exhibited base changes at 2-6 positions of 2019-base 18S rDNA, at 5-29 positions of 1817/1818-base 28Salpha rDNA, or 1-5 positions of 1557-1559-base 28Sbeta rDNA, and none was separated from the other 2 isolates by rDNA nucleotide sequences. Since base changes of Herpetosoma trypanosomes at the level of inter- and intra-species might occur frequently in specified rDNA regions, the molecular analysis on these regions of rodent trypanosomes could help species/strain differentiation and systematic revision of Herpetosoma trypanosome species, which must be more abundant than presently known.

A new lineage of trypanosomes from Australian vertebrates and terrestrial bloodsucking leeches (Haemadipsidae)

Little is known about the trypanosomes of indigenous Australian vertebrates and their vectors. We surveyed a range of vertebrates and blood-feeding invertebrates for trypanosomes by parasitological and PCR-based methods using primers specific to the small subunit ribosomal RNA (SSU rRNA) gene of genus Trypanosoma. Trypanosome isolates were obtained in culture from two common wombats, one swamp wallaby and an Australian bird (Strepera sp.). By PCR, blood samples from three wombats, one brush-tailed wallaby, three platypuses and a frog were positive for trypanosome DNA. All the blood-sucking invertebrates screened were negative for trypanosomes both by microscopy and PCR, except for specimens of terrestrial leeches (Haemadipsidae). Of the latter, two Micobdella sp. specimens from Victoria and 18 Philaemon sp. specimens from Queensland were positive by PCR. Four Haemadipsa zeylanica specimens from Sri Lanka and three Leiobdella jawarerensis specimens from Papua New Guinea were also PCR positive for trypanosome DNA. We sequenced the SSU rRNA and glycosomal glyceraldehyde phosphate dehydrogenase (gGAPDH) genes in order to determine the phylogenetic positions of the new vertebrate and terrestrial leech trypanosomes. In trees based on these genes, Australian vertebrate trypanosomes fell in several distinct clades, for the most part being more closely related to trypanosomes outside Australia than to each other. Two previously undescribed wallaby trypanosomes fell in a clade with Trypanosoma theileri, the cosmopolitan bovid trypanosome, and Trypanosoma cyclops from a Malaysian primate. The terrestrial leech trypanosomes were closely related to the wallaby trypanosomes, T. cyclops and a trypanosome from an Australian frog. We suggest that haemadipsid leeches may be significant and widespread vectors of trypanosomes in Australia and Asia.

Phylogeny, taxonomy and grouping of Trypanosoma rangeli isolates from man, triatomines and sylvatic mammals from widespread geographical origin based on SSU and ITS ribosomal sequences

Phylogenetic relationships among Trypanosoma rangeli isolates from man, wild mammals and triatomine bugs from widespread geographical origin were inferred by comparison of the small subunit of ribosomal gene sequences. The phylogenetic trees indicated that the subgenus Herpetosoma is polyphyletic and strongly supported division of this group into two monophyletic lineages, one made up of T. rangeli, T. rangeli-like and allied species and other consisting of T. lewisi and related taxa. Based on phylogenetic analysis, morphology, behaviour in vertebrate and invertebrate hosts and epidemiology we propose: a) the validation of Herpetosoma as a taxon comprised only for species of group lewisi and the maintenance of T. lewisi as the type-species of this subgenus; b) the classification of T. rangeli, T. rangeli-like and allied species into a ‘T. rangeli-clade’ more closely related to Schizotrypanum than to T. lewisi or T. brucei. The phylogenetic tree disclosed at least 4 groups within the clade T. rangeli, all confirmed by polymorphism of the internal transcribed spacer, thus conferring for the first time phylogenetic support to groups of T. rangeli and corroborating the high complexity of this taxon. Grouping was independent of their mammalian host-species and geographical origin, indicating that other factors are determining this segregation.

RNA-interference silencing of the adenosine transporter-1 gene in Trypanosoma evansi confers resistance to diminazene aceturate

Drug resistance of trypanosomes is now a problem, but its underlying mechanisms are not fully understood. Cellular uptake of the major trypanocidal drugs is thought to occur through an adenosine transporter. The adenosine transporter-1 gene, TbAT1, encoding a P2-like nucleoside transporter has previously been cloned from Trypanosoma brucei brucei, and when expressed in yeast, it showed very similar substrate specificity to the P2-nucleoside transporter, but could not transport diamidines (pentamidine and diminazene). We have cloned and sequenced a similar gene (TevAT1) from Trypanosoma evansi and found it to have 99.7% identity to the TbAT1 gene. To elucidate the role of the TevAT1 gene on diamidine trypanocidal effect, we genetically engineered T. evansi for conditional knock-out of the TevAT1 gene by RNA interference (RNAi). Induction of the RNAi resulted in 10-fold depletion of TevAT1 mRNA, with concomitantly significant resistance to diminazene aceturate (berenil). The induced parasites propagated normally and attained peak cell density at an in vitro concentration of berenil, 5.5-fold higher than the IC(100) of the wild-type. TevAT1 knock-out had no effect on the trypanocidal activity of suramin and antrycide, but conferred some resistance to samorin. Our findings validate the significance of the TevAT1 adenosine transporter-1 gene in mediating the trypanocidal effect of diamidines in T. evansi. Further, we show for the first time that RNAi gene silencing in T. evansi can be induced using plasmids designed for T. brucei. We also demonstrate the usefulness of real-time PCR in rapidly quantifying mRNA levels in trypanosomes.

Small nucleolar RNAs that guide modification in trypanosomatids: repertoire, targets, genome organisation, and unique functions

Small nucleolar RNAs constitute a family of newly discovered non-coding small RNAs, most of which function in guiding RNA modifications. Two prevalent types of modifications are 2'-O-methylation and pseudouridylation. The modification is directed by the formation of a canonical small nucleolar RNA-target duplex. Initially, RNA-guided modification was shown to take place on rRNA, but recent studies suggest that small nuclear RNA, mRNA, tRNA, and the trypanosome spliced leader RNA also undergo guided modifications. Trypanosomes contain more modifications and potentially more small nucleolar RNAs than yeast, and the increased number of modifications may help to preserve ribosome function under adverse environmental conditions during the cycling between the insect and mammalian host. The genome organisation in clusters carrying the two types of small nucleolar RNAs, C/D and H/ACA-like RNAs, resembles that in plants. However, the trypanosomatid H/ACA RNAs are similar to those found in Archaea and are composed of a single hairpin that may represent the primordial H/ACA RNA. In this review we summarise this new field of trypanosome small nucleolar RNAs, emphasising the open questions regarding the number of small nucleolar RNAs, the repertoire, genome organisation, and the unique function of guided modifications in these protozoan parasites.

Identification and functional characterization of lsm proteins in Trypanosoma brucei

RNA interference of Sm proteins in Trypanosoma brucei demonstrated that the stability of the small nuclear RNAs (U1, U2, U4, U5) and the spliced leader RNA, but not U6 RNA, were affected upon Sm depletion (Mandelboim, M., Barth, S., Biton, M., Liang, X. H., and Michaeli, S. (2003) J. Biol. Chem. 278, 51469-51478), suggesting that Lsm proteins that bind and stabilize U6 RNA in other eukaryotes should exist in trypanosomes. In this study, we identified seven Lsm proteins (Lsm2p to Lsm8p) and examined the function of Lsm3p and Lsm8p by RNA interference silencing. Both Lsm proteins were found to be essential for U6 stability and mRNA decay. Silencing was lethal, and cis- and trans-splicing were inhibited. Importantly, silencing also affected the level of U4.U6 and the U4.U6/U5 tri-small nuclear ribonucleoprotein complexes. The presence of Lsm proteins in trypanosomes that diverged early in the eukaryotic lineage suggests that these proteins are highly conserved in both structure and function among eukaryotes. Interestingly, however, Lsm1p that is specific to the mRNA decay complex was not identified in the genome data base of any kinetoplastidae, and the Lsm8p that in other eukaryotes exclusively functions in U6 stability was found to function in trypanosomes also in mRNA decay. These data therefore suggest that in trypanosomes only a single Lsm complex may exist.

A new species of trypanosome, Trypanosoma desterrensis sp. n., isolated from South American bats

Trypanosomes isolated from South American bats include the human pathogen Trypanosoma cruzi. Other Trypanosoma spp. that have been found exclusively in bats are not well characterized at the DNA sequence level and we have therefore used the SL RNA gene to differentiate and characterize kinetoplastids isolated from bats in South America. A Trypanosoma sp. isolated from hats in southern Brazil was compared with the geographically diverse isolates T. cruzi marinkellei, T. vespertilionis, and T. dionisii. Analysis of the SL RNA gene repeats revealed size and sequence variability among these bat trypanosomes. We have developed hybridization probes to separate these bat isolates and have analysed the DNA sequence data to estimate their relatedness. A new species, Trypanosoma desterrensis sp. n., is proposed, for which a 5S rRNA gene was also found within the SL RNA repeat.

Non-pathogenic trypanosomatid protozoa as a platform for protein research and production

All currently existing eukaryotic protein expression systems are based on autonomous life forms. To exploit the potential practical benefits associated with parasitic organisms we have developed a new protein expression system based on Leishmania tarentolae (Trypanosomatidae), a protozoan parasite of lizards. To achieve strong transcription, the genes of interest were integrated into the small subunit ribosomal RNA gene. Expression levels obtained were up to 30 mg of recombinant protein per liter of suspension culture and increased linearly with the number of integrated gene copies. To assess the system's potential for production of post-translationally modified proteins, we have expressed human erythropoietin in L. tarentolae. The recombinant protein isolated from the culture supernatants was biologically active, natively processed at the N-terminus, and N-glycosylated. The N-glycosylation was exceptionally homogeneous, with a mammalian-type biantennary oligosaccharide and the Man(3)GlcNAc(2) core structure accounting for >90% of the glycans present. L. tarentolae is thus the first described biotechnologically useful unicellular eukaryotic organism producing biantennary fully galactosylated, core-alpha-1,6-fucosylated N-glycans.

Evidence for a wide occurrence of proton-translocating pyrophosphatase genes in parasitic and free-living protozoa

Proton-translocating inorganic pyrophosphatases (H(+)-PPase, EC 3.6.1.1) are integral membrane proteins that have been extensively studied in higher plants, the photosynthetic bacterium Rhodospirillum rubrum and, more recently, in some human pathogenic protozoa. By using a PCR-based approach, fragments of genes coding for H(+)-PPases in a number of protists, both free-living and parasites of animals and plants, that belong to diverse taxonomic groups (trypanosomatids, ciliates, apicomplexans, euglenoids, amoeboid mycetozoa, heterokonts) have been isolated. The experimental procedure involved the use of degenerate oligonucleotides designed from protein domains conserved in H(+)-PPases from plants and bacteria. The PCR-amplified DNA fragments exhibited the characteristic genomic structure and codon usage of the corresponding protozoan group. Paralogous genes were found in some species suggesting the occurrence of protein isoforms. These results indicate that H(+)-PPases are more widely distributed among protozoa than previously thought.

Phylogenetic position of the giant anuran trypanosomes Trypanosoma chattoni, Trypanosoma fallisi, Trypanosoma mega, Trypanosoma neveulemairei, and Trypanosoma ranarum inferred from 18S rRNA gene sequences

Phylogenetic relationships within the kinetoplastid flagellates were inferred from comparisons of small-subunit ribosomal RNA gene sequences. These included 5 new gene sequences, Trypanosoma fallisi (2,239 bp), Trypanosoma chattoni (2,180 bp), Trypanosoma mega (2,211 bp), Trypanosoma neveulemairei (2,197 bp), and Trypanosoma ranarum (2,203 bp). Trees produced using maximum-parsimony and distance-matrix methods (least-squares, neighbor-joining, and maximum-likelihood), supported by strong bootstrap and quartet-puzzle analyses, indicated that the trypanosomes are a monophyletic group that divides into 2 major lineages, the salivarian trypanosomes and the nonsalivarian trypanosomes. The nonsalivarian trypanosomes further divide into 2 lineages, 1 containing trypanosomes of birds, mammals, and reptiles and the other containing trypanosomes of fish, reptiles, and anurans. Among the giant trypanosomes, T. chattoni is clearly shown to be distantly related to all the other anuran trypanosome species. Trypanosoma mega is closely associated with T. fallisi and T. ranarum, whereas T. neveulemairei and Trypanosoma rotatorium are sister taxa. The branching order of the anuran trypanosomes suggests that some toad trypanosomes may have evolved by host switching from frogs to toads.