Phylogenomic study indicates widespread lateral gene transfer in Entamoeba and suggests a past intimate relationship with parabasalids

Phylogenomic workflow for uncultivable microbial eukaryotes using single-cell RNA sequencing - A case study with planktonic ciliates (Ciliophora, Oligotrichea)

Phylogenetic analyses increasingly rely on genomic and transcriptomic data to produce better supported inferences on the evolutionary relationships among microbial eukaryotes. Such phylogenomic analyses, however, require robust workflows, bioinformatic expertise and computational power. Microbial eukaryotes pose additional challenges given the complexity of their genomes and the presence of non-target sequences (e.g., symbionts, prey) in data obtained from single cells of uncultivable lineages. To address these challenges, we developed a phylogenomic workflow based on single-cell RNA sequencing, integrating all essential steps from cell isolation to data curation and species tree inference. We assessed our workflow by using publicly available and newly generated transcriptomes (11 and 28, respectively) from the Oligotrichea, a diverse group of marine planktonic ciliates. This group's phylogenetic relationships have been relatively well-studied based on ribosomal RNA gene markers, which we reconstructed by read mapping of transcriptome sequences and compared to our phylogenomic inferences. We also compared phylogenomic analyses based on single-copy protein-coding genes (well-curated orthologs) and multi-copy genes (including paralogs) by sequence concatenation and a coalescence approach (Asteroid), respectively. Finally, using subsets of up to 1,014 gene families (GFs), we assessed the influence of missing data in our phylogenomic inferences. All our analyses yielded similar results, and most inferred relationships were consistent and well-supported. Overall, we found that Asteroid provides robust support for species tree inferences, while simplifying curation steps, minimizing the effects of missing data and maximizing the number of GFs represented in the analyses. Our workflow can be adapted for phylogenomic analyses based on single-cell RNA sequencing of other uncultivable microbial eukaryotes.

Pathogenicity and virulence of Entamoeba histolytica, the agent of amoebiasis

The amoeba parasite Entamoeba histolytica is the causative agent of human amebiasis, an enteropathic disease affecting millions of people worldwide. This ancient protozoan is an elementary example of how parasites evolve with humans, e.g. taking advantage of multiple mechanisms to evade immune responses, interacting with microbiota for nutritional and protective needs, utilizing host resources for growth, division, and encystation. These skills of E. histolytica perpetuate the species and incidence of infection. However, in 10% of infected cases, the parasite turns into a pathogen; the host-parasite equilibrium is then disorganized, and the simple lifecycle based on two cell forms, trophozoites and cysts, becomes unbalanced. Trophozoites acquire a virulent phenotype which, when non-controlled, leads to intestinal invasion with the onset of amoebiasis symptoms. Virulent E. histolytica must cross mucus, epithelium, connective tissue and possibly blood. This highly mobile parasite faces various stresses and a powerful host immune response, with oxidative stress being a challenge for its survival. New emerging research avenues and omics technologies target gene regulation to determine human or parasitic factors activated upon infection, their role in virulence activation, and in pathogenesis; this research bears in mind that E. histolytica is a resident of the complex intestinal ecosystem. The goal is to eradicate amoebiasis from the planet, but the parasitic life of E. histolytica is ancient and complex and will likely continue to evolve with humans. Advances in these topics are summarized here.

Presence of CRISPR CAS-Like Sequences as a Proposed Mechanism for Horizontal Genetic Exchanges between Trichomonas vaginalis and Its Associated Virus: A Comparative Genomic Analysis with the First Report of a Putative CRISPR CAS Structures in Eukaryotic Cells

Introduction

Trichomonas vaginalis genome is among the largest genome size and coding capacities. Combinations of gene duplications, transposon, repeated sequences, and lateral gene transfers (LGTs) have contributed to the unexpected large genomic size and diversity. This study is aimed at investigating genomic exchange and seeking for presence of the CRISPR CAS system as one of the possible mechanisms for some level of genetic exchange. Material and Methods. In this comparative analysis, 398 publicly available Trichomonas vaginalis complete genomes were investigated for the presence of CRISPR CAS. Spacer sequences were also analyzed for their origin using BLAST.

Results

We identified a CRISPR CAS (Cas3). CRISPR spacers are highly similar to transposable genetic elements such as viruses of protozoan parasites, especially megavirals, some transposons, and, interestingly, papillomavirus and HIV-1 in a few cases. Discussion. There is a striking similarity between the prokaryotes/Archaean CRISPR and what we find as eukaryotic CRISPR. About 5-10% of the 398 T. vaginalis possess a CRISPR structure.

Conclusion

According to sequences and their organization, we assume that these repeated sequences and spacer, along with their mentioned features, could be the eukaryotic homolog of prokaryotes and Archaean CRISPR systems and may involve in a process similar to the CRISPR function.

Old genes in new places: A taxon-rich analysis of interdomain lateral gene transfer events

Vertical inheritance is foundational to Darwinian evolution, but fails to explain major innovations such as the rapid spread of antibiotic resistance among bacteria and the origin of photosynthesis in eukaryotes. While lateral gene transfer (LGT) is recognized as an evolutionary force in prokaryotes, the role of LGT in eukaryotic evolution is less clear. With the exception of the transfer of genes from organelles to the nucleus, a process termed endosymbiotic gene transfer (EGT), the extent of interdomain transfer from prokaryotes to eukaryotes is highly debated. A common critique of studies of interdomain LGT is the reliance on the topology of single-gene trees that attempt to estimate more than one billion years of evolution. We take a more conservative approach by identifying cases in which a single clade of eukaryotes is found in an otherwise prokaryotic gene tree (i.e. exclusive presence). Starting with a taxon-rich dataset of over 13,600 gene families and passing data through several rounds of curation, we identify and categorize the function of 306 interdomain LGT events into diverse eukaryotes, including 189 putative EGTs, 52 LGTs into Opisthokonta (i.e. animals, fungi and their microbial relatives), and 42 LGTs nearly exclusive to anaerobic eukaryotes. To assess differential gene loss as an explanation for exclusive presence, we compare branch lengths within each LGT tree to a set of vertically-inherited genes subsampled to mimic gene loss (i.e. with the same taxonomic sampling) and consistently find shorter relative distance between eukaryotes and prokaryotes in LGT trees, a pattern inconsistent with gene loss. Our methods provide a framework for future studies of interdomain LGT and move the field closer to an understanding of how best to model the evolutionary history of eukaryotes.

Epigenetic influences of mobile genetic elements on ciliate genome architecture and evolution

Mobile genetic elements (MGEs) are transient genetic material that can move either within a single organism's genome or between individuals or species. While historically considered 'junk' DNA (i.e. deleterious or at best neutral), more recent studies reveal the adaptive advantages MGEs provide in lineages across the tree of life. Ciliates, a group of single-celled microbial eukaryotes characterized by nuclear dimorphism, exemplify how epigenetic influences from MGEs shape genome architecture and patterns of molecular evolution. Ciliate nuclear dimorphism may have evolved as a response to transposon invasion and ciliates have since co-opted transposons to carry out programmed DNA deletion. Another example of the effect of MGEs is in providing mechanisms for lateral gene transfer from bacteria, which introduces genetic diversity and, in several cases, drives ecological specialization in ciliates. As a third example, the integration of viral DNA, likely through transduction, provides new genetic material and can change the way host cells defend themselves against other viral pathogens. We argue that the acquisition of MGEs through non-Mendelian patterns of inheritance, coupled with their effects on ciliate genome architecture and expression and persistence throughout evolutionary history, exemplify how the transmission of mobile elements should be considered a mechanism of transgenerational epigenetic inheritance.

The Mastigamoeba balamuthi Genome and the Nature of the Free-Living Ancestor of Entamoeba

The transition of free-living organisms to parasitic organisms is a mysterious process that occurs in all major eukaryotic lineages. Parasites display seemingly unique features associated with their pathogenicity; however, it is important to distinguish ancestral preconditions to parasitism from truly new parasite-specific functions. Here, we sequenced the genome and transcriptome of anaerobic free-living Mastigamoeba balamuthi and performed phylogenomic analysis of four related members of the Archamoebae, including Entamoeba histolytica, an important intestinal pathogen of humans. We aimed to trace gene histories throughout the adaptation of the aerobic ancestor of Archamoebae to anaerobiosis and throughout the transition from a free-living to a parasitic lifestyle. These events were associated with massive gene losses that, in parasitic lineages, resulted in a reduction in structural features, complete losses of some metabolic pathways, and a reduction in metabolic complexity. By reconstructing the features of the common ancestor of Archamoebae, we estimated preconditions for the evolution of parasitism in this lineage. The ancestor could apparently form chitinous cysts, possessed proteolytic enzyme machinery, compartmentalized the sulfate activation pathway in mitochondrion-related organelles, and possessed the components for anaerobic energy metabolism. After the split of Entamoebidae, this lineage gained genes encoding surface membrane proteins that are involved in host–parasite interactions. In contrast, gene gains identified in the M. balamuthi lineage were predominantly associated with polysaccharide catabolic processes. A phylogenetic analysis of acquired genes suggested an essential role of lateral gene transfer in parasite evolution (Entamoeba) and in adaptation to anaerobic aquatic sediments (Mastigamoeba).

Fungal evolution: cellular, genomic and metabolic complexity

The question of how phenotypic and genomic complexity are inter-related and how they are shaped through evolution is a central question in biology that historically has been approached from the perspective of animals and plants. In recent years, however, fungi have emerged as a promising alternative system to address such questions. Key to their ecological success, fungi present a broad and diverse range of phenotypic traits. Fungal cells can adopt many different shapes, often within a single species, providing them with great adaptive potential. Fungal cellular organizations span from unicellular forms to complex, macroscopic multicellularity, with multiple transitions to higher or lower levels of cellular complexity occurring throughout the evolutionary history of fungi. Similarly, fungal genomes are very diverse in their architecture. Deep changes in genome organization can occur very quickly, and these phenomena are known to mediate rapid adaptations to environmental changes. Finally, the biochemical complexity of fungi is huge, particularly with regard to their secondary metabolites, chemical products that mediate many aspects of fungal biology, including ecological interactions. Herein, we explore how the interplay of these cellular, genomic and metabolic traits mediates the emergence of complex phenotypes, and how this complexity is shaped throughout the evolutionary history of Fungi.

Lateral Acquisitions Repeatedly Remodel the Oxygen Detoxification Pathway in Diplomonads and Relatives

Oxygen and reactive oxygen species (ROS) are important stress factors for cells because they can oxidize many large molecules. Fornicata, a group of flagellated protists that includes diplomonads, have anaerobic metabolism but are still able to tolerate fluctuating levels of oxygen. We identified 25 protein families putatively involved in detoxification of oxygen and ROS in this group using a bioinformatics approach and propose how these interact in an oxygen detoxification pathway. These protein families were divided into a central oxygen detoxification pathway and accessory pathways for the synthesis of nonprotein thiols. We then used a phylogenetic approach to investigate the evolutionary origin of the components of this putative pathway in Diplomonadida and other Fornicata species. Our analyses suggested that the diplomonad ancestor was adapted to low-oxygen levels, was able to reduce O₂ to H₂O in a manner similar to extant diplomonads, and was able to synthesize glutathione and l-cysteine. Several genes involved in the pathway have complex evolutionary histories and have apparently been repeatedly acquired through lateral gene transfer and subsequently lost. At least seven genes were acquired independently in different Fornicata lineages, leading to evolutionary convergences. It is likely that acquiring these oxygen detoxification proteins helped anaerobic organisms (like the parasitic Giardia intestinalis) adapt to low-oxygen environments (such as the digestive tract of aerobic hosts).

PhyloToL: A Taxon/Gene-Rich Phylogenomic Pipeline to Explore Genome Evolution of Diverse Eukaryotes

Estimating multiple sequence alignments (MSAs) and inferring phylogenies are essential for many aspects of comparative biology. Yet, many bioinformatics tools for such analyses have focused on specific clades, with greatest attention paid to plants, animals, and fungi. The rapid increase in high-throughput sequencing (HTS) data from diverse lineages now provides opportunities to estimate evolutionary relationships and gene family evolution across the eukaryotic tree of life. At the same time, these types of data are known to be error-prone (e.g., substitutions, contamination). To address these opportunities and challenges, we have refined a phylogenomic pipeline, now named PhyloToL, to allow easy incorporation of data from HTS studies, to automate production of both MSAs and gene trees, and to identify and remove contaminants. PhyloToL is designed for phylogenomic analyses of diverse lineages across the tree of life (i.e., at scales of >100 My). We demonstrate the power of PhyloToL by assessing stop codon usage in Ciliophora, identifying contamination in a taxon- and gene-rich database and exploring the evolutionary history of chromosomes in the kinetoplastid parasite Trypanosoma brucei, the causative agent of African sleeping sickness. Benchmarking PhyloToL’s homology assessment against that of OrthoMCL and a published paper on superfamilies of bacterial and eukaryotic organellar outer membrane pore-forming proteins demonstrates the power of our approach for determining gene family membership and inferring gene trees. PhyloToL is highly flexible and allows users to easily explore HTS data, test hypotheses about phylogeny and gene family evolution and combine outputs with third-party tools (e.g., PhyloChromoMap, iGTP).

Transposable Elements Cross Kingdom Boundaries and Contribute to Inflammation and Ageing: Somatic Acquisition of Foreign Transposable Elements as a Catalyst of Genome Instability, Epigenetic Dysregulation, Inflammation, Senescence, and Ageing

The de-repression of transposable elements (TEs) in mammalian genomes is thought to contribute to genome instability, inflammation, and ageing, yet is viewed as a cell-autonomous event. In contrast to mammalian cells, prokaryotes constantly exchange genetic material through TEs, crossing both cell and species barriers, contributing to rapid microbial evolution and diversity in complex communities such as the mammalian gut. Here, it is proposed that TEs released from prokaryotes in the microbiome or from pathogenic infections regularly cross the kingdom barrier to the somatic cells of their eukaryotic hosts. It is proposed this horizontal transfer of TEs from microbe to host is a stochastic, ongoing catalyst of genome destabilization, resulting in structural and epigenetic variations, and activation of well-evolved host defense mechanisms contributing to inflammation, senescence, and biological ageing. It is proposed that innate immunity pathways defend against the horizontal acquisition of microbial TEs, and that activation of this pathway during horizontal transposon transfer promotes chronic inflammation during ageing. Finally, it is suggested that horizontal acquisition of prokaryotic TEs into mammalian genomes has been masked and subsequently under-reported due to flaws in current sequencing pipelines, and new strategies to uncover these events are proposed.

Horizontal Gene Transfer as an Indispensable Driver for Evolution of Neocallimastigomycota into a Distinct Gut-Dwelling Fungal Lineage

Survival and growth of the anaerobic gut fungi (AGF; Neocallimastigomycota) in the herbivorous gut necessitate the possession of multiple abilities absent in other fungal lineages. We hypothesized that horizontal gene transfer (HGT) was instrumental in forging the evolution of AGF into a phylogenetically distinct gut-dwelling fungal lineage. The patterns of HGT were evaluated in the transcriptomes of 27 AGF strains, 22 of which were isolated and sequenced in this study, and 4 AGF genomes broadly covering the breadth of AGF diversity. We identified 277 distinct incidents of HGT in AGF transcriptomes, with subsequent gene duplication resulting in an HGT frequency of 2 to 3.5% in AGF genomes. The majority of HGT events were AGF specific (91.7%) and wide (70.8%), indicating their occurrence at early stages of AGF evolution. The acquired genes allowed AGF to expand their substrate utilization range, provided new venues for electron disposal, augmented their biosynthetic capabilities, and facilitated their adaptation to anaerobiosis. The majority of donors were anaerobic fermentative bacteria prevalent in the herbivorous gut. This study strongly indicates that HGT indispensably forged the evolution of AGF as a distinct fungal phylum and provides a unique example of the role of HGT in shaping the evolution of a high-rank taxonomic eukaryotic lineage.IMPORTANCE The anaerobic gut fungi (AGF) represent a distinct basal phylum lineage (Neocallimastigomycota) commonly encountered in the rumen and alimentary tracts of herbivores. Survival and growth of anaerobic gut fungi in these anaerobic, eutrophic, and prokaryote-dominated habitats necessitates the acquisition of several traits absent in other fungal lineages. We assess here the role of horizontal gene transfer as a relatively fast mechanism for trait acquisition by the Neocallimastigomycota postsequestration in the herbivorous gut. Analysis of 27 transcriptomes that represent the broad diversity of Neocallimastigomycota identified 277 distinct HGT events, with subsequent gene duplication resulting in an HGT frequency of 2 to 3.5% in AGF genomes. These HGT events have allowed AGF to survive in the herbivorous gut by expanding their substrate utilization range, augmenting their biosynthetic pathway, providing new routes for electron disposal by expanding fermentative capacities, and facilitating their adaptation to anaerobiosis. HGT in the AGF is also shown to be mainly a cross-kingdom affair, with the majority of donors belonging to the bacteria. This study represents a unique example of the role of HGT in shaping the evolution of a high-rank taxonomic eukaryotic lineage.

Atypical Evolution of the F1Fo Adenosine Triphosphate Synthase Regulatory ATP6 subunit in Glacier Ice Worms (Annelida: Clitellata: Mesenchytraeus)

The glacier ice worm, Mesenchytraeus solifugus, is among a few animals that reside permanently in glacier ice. Their adaptation to cold temperature has been linked to relatively high intracellular adenosine triphosphate (ATP) levels, which compensate for reductions in molecular motion at low physiological temperatures. Here, we show that ATP6-the critical regulatory subunit of the F1Fo-ATP synthase and primary target of mitochondrial disease-acquired an unprecedented histidine-rich, 18-amino acid carboxy-terminal extension, which counters the strong evolutionary trend of mitochondrial genome compaction. Furthermore, sequence analysis suggests that this insertion is not of metazoan origin, but rather is a product of horizontal gene transfer from a microbial dietary source, and may act as a proton shuttle to accelerate the rate of ATP synthesis.

The evolutionary origin and possible functional roles of FNIII domains in two Microbacterium aurum B8.A granular starch degrading enzymes, and in other carbohydrate acting enzymes

Fibronectin type III (FNIII) domains were first identified in the eukaryotic plasma protein fibronectin, where they act as structural spacers or enable protein-protein interactions. Recently we characterized two large and multi-domain amylases in Microbacterium aurum B8.A that both carry multiple FNIII and carbohydrate binding modules (CBMs). The role of (multiple) FNIII domains in such carbohydrate acting enzymes is currently unclear. Four hypothetical functions are considered here: a substrate surface disruption domain, a carbohydrate binding module, as a stable linker, or enabling protein-protein interactions. We performed a phylogenetic analysis of all FNIII domains identified in proteins listed in the CAZy database. These data clearly show that the FNIII domains in eukaryotic and archaeal CAZy proteins are of bacterial origin and also provides examples of interkingdom gene transfer from Bacteria to Archaea and Eucarya. FNIII domains occur in a wide variety of CAZy enzymes acting on many different substrates, suggesting that they have a non-specific role in these proteins. While CBM domains are mostly found at protein termini, FNIII domains are commonly located between other protein domains. FNIII domains in carbohydrate acting enzymes thus may function mainly as stable linkers to allow optimal positioning and/or flexibility of the catalytic domain and other domains, such as CBM.

Widespread Inter- and Intra-Domain Horizontal Gene Transfer of d-Amino Acid Metabolism Enzymes in Eukaryotes

Analysis of the growing number of available fully-sequenced genomes has shown that Horizontal Gene Transfer (HGT) in eukaryotes is more common than previously thought. It has been proposed that genes with certain functions may be more prone to HGT than others, but we still have a very poor understanding of the selective forces driving eukaryotic HGT. Recent work uncovered that d-amino acid racemases have been commonly transferred from bacteria to fungi, but their role in the receiving organisms is currently unknown. Here, we set out to assess whether d-amino acid racemases are commonly transferred to and between eukaryotic groups. For this we performed a global survey that used a novel automated phylogeny-based HGT-detection algorithm (Abaccus). Our results revealed that at least 7.0% of the total eukaryotic racemase repertoire is the result of inter- or intra-domain HGT. These transfers are significantly enriched in plant-associated fungi. For these, we hypothesize a possible role for the acquired racemases allowing to exploit minoritary nitrogen sources in plant biomass, a nitrogen-poor environment. Finally, we performed experiments on a transferred aspartate-glutamate racemase in the fungal human pathogen Candida glabrata, which however revealed no obvious biological role.

Cymbomonas tetramitiformis - a peculiar prasinophyte with a taste for bacteria sheds light on plastid evolution

Cymbomonas tetramitiformis is a peculiar green alga that unites in one cell the abilities of photosynthesis and phagocytosis, which makes it a very useful model for the study of the evolution of plastid endosymbiosis. We have pondered over this issue and propose an evolutionary scenario of trophic strategies in eukaryotes, including primary and secondary plastid endosymbioses. C. tetramitiformis is a prototroph, just like the common ancestor of Archaeplastida was, and can synthesize most small organic molecules contrary to other eukaryotic phagotrophs, e.g. some metazoans, amoebozoans, and ciliates, which have not evolved tight endosymbiotic relationships. In order to establish a permanent photosynthetic endosymbiont they do not have to become prototrophs, but have to acquire the genes necessary for plastid retention via horizontal (including endosymbiotic) gene transfer. Such processes occurred successfully in the ancestors of eukaryotes with permanent secondary plastids and thus led to their great diversification. The preservation of phagocytosis in Cymbomonas (and some other prasinophytes as well) seems to result from nutrient deficiency in their oligotrophic habitats. This forces them to supplement their diet with phagocytized prey, in contrasts to the thecate amoeba Paulinella chromatophora, which also successfully transformed cyanobacteria into permanent organelles. Although Paulinella endosymbionts were acquired very recently in comparison to primary plastids, Paulinella has lost the ability to phagocytose, most probably due to the fact that it inhabits nutrient-rich environments, which renders the phagotrophy nonessential.

A natural barrier to lateral gene transfer from prokaryotes to eukaryotes revealed from genomes: the 70 % rule

BACKGROUND

The literature harbors many claims for lateral gene transfer (LGT) from prokaryotes to eukaryotes. Such claims are typically founded in analyses of genome sequences. It is undisputed that many genes entered the eukaryotic lineage via the origin of mitochondria and the origin of plastids. Claims for lineage-specific LGT to eukaryotes outside the context of organelle origins and claims of continuous LGT to eukaryotic lineages are more problematic. If eukaryotes acquire genes from prokaryotes continuously during evolution, then sequenced eukaryote genomes should harbor evidence for recent LGT, like prokaryotic genomes do.

RESULTS

Here we devise an approach to investigate 30,358 eukaryotic sequences in the context of 1,035,375 prokaryotic homologs among 2585 phylogenetic trees containing homologs from prokaryotes and eukaryotes. Prokaryote genomes reflect a continuous process of gene acquisition and inheritance, with abundant recent acquisitions showing 80-100 % amino acid sequence identity to their phylogenetic sister-group homologs from other phyla. By contrast, eukaryote genomes show no evidence for either continuous or recent gene acquisitions from prokaryotes. We find that, in general, genes in eukaryotic genomes that share ≥70 % amino acid identity to prokaryotic homologs are genome-specific; that is, they are not found outside individual genome assemblies.

CONCLUSIONS

Our analyses indicate that eukaryotes do not acquire genes through continual LGT like prokaryotes do. We propose a 70 % rule: Coding sequences in eukaryotic genomes that share more than 70 % amino acid sequence identity to prokaryotic homologs are most likely assembly or annotation artifacts. The findings further uncover that the role of differential loss in eukaryote genome evolution has been vastly underestimated.

Bulky Trichomonad Genomes: Encoding a Swiss Army Knife

The trichomonads are a remarkably successful lineage of ancient, predominantly parasitic protozoa. Recent molecular analyses have revealed extensive duplication of certain genetic loci in trichomonads. Consequently, their genomes are exceptionally large compared to other parasitic protozoa. Retention of these large gene expansions across different trichomonad families raises the question: do these duplications afford an advantage? Many duplicated genes are linked to the parasitic lifestyle and some are regulated differently to their paralogues, suggesting they have acquired new functions. It is proposed that these large genomes encode a Swiss army knife of sorts, packed with a multitude of tools for use in many different circumstances. This may have bestowed trichomonads with the extraordinary versatility that has undoubtedly contributed to their success.

Recent events dominate interdomain lateral gene transfers between prokaryotes and eukaryotes and, with the exception of endosymbiotic gene transfers, few ancient transfer events persist

While there is compelling evidence for the impact of endosymbiotic gene transfer (EGT; transfer from either mitochondrion or chloroplast to the nucleus) on genome evolution in eukaryotes, the role of interdomain transfer from bacteria and/or archaea (i.e. prokaryotes) is less clear. Lateral gene transfers (LGTs) have been argued to be potential sources of phylogenetic information, particularly for reconstructing deep nodes that are difficult to recover with traditional phylogenetic methods. We sought to identify interdomain LGTs by using a phylogenomic pipeline that generated 13 465 single gene trees and included up to 487 eukaryotes, 303 bacteria and 118 archaea. Our goals include searching for LGTs that unite major eukaryotic clades, and describing the relative contributions of LGT and EGT across the eukaryotic tree of life. Given the difficulties in interpreting single gene trees that aim to capture the approximately 1.8 billion years of eukaryotic evolution, we focus on presence-absence data to identify interdomain transfer events. Specifically, we identify 1138 genes found only in prokaryotes and representatives of three or fewer major clades of eukaryotes (e.g. Amoebozoa, Archaeplastida, Excavata, Opisthokonta, SAR and orphan lineages). The majority of these genes have phylogenetic patterns that are consistent with recent interdomain LGTs and, with the notable exception of EGTs involving photosynthetic eukaryotes, we detect few ancient interdomain LGTs. These analyses suggest that LGTs have probably occurred throughout the history of eukaryotes, but that ancient events are not maintained unless they are associated with endosymbiotic gene transfer among photosynthetic lineages.

Horizontal Gene Transfers from Bacteria to Entamoeba Complex: A Strategy for Dating Events along Species Divergence

Horizontal gene transfer has proved to be relevant in eukaryotic evolution, as it has been found more often than expected and related to adaptation to certain niches. A relatively large list of laterally transferred genes has been proposed and evaluated for the parasite Entamoeba histolytica. The goals of this work were to elucidate the importance of lateral gene transfer along the evolutionary history of some members of the genus Entamoeba, through identifying donor groups and estimating the divergence time of some of these events. In order to estimate the divergence time of some of the horizontal gene transfer events, the dating of some Entamoeba species was necessary, following an indirect dating strategy based on the fossil record of plausible hosts. The divergence between E. histolytica and E. nuttallii probably occurred 5.93 million years ago (Mya); this lineage diverged from E. dispar 9.97 Mya, while the ancestor of the latter separated from E. invadens 68.18 Mya. We estimated times for 22 transferences; the most recent occurred 31.45 Mya and the oldest 253.59 Mya. Indeed, the acquisition of genes through lateral transfer may have triggered a period of adaptive radiation, thus playing a major role in the evolution of the Entamoeba genus.

Horizontal gene transfer: building the web of life

Horizontal gene transfer (HGT) is the sharing of genetic material between organisms that are not in a parent-offspring relationship. HGT is a widely recognized mechanism for adaptation in bacteria and archaea. Microbial antibiotic resistance and pathogenicity are often associated with HGT, but the scope of HGT extends far beyond disease-causing organisms. In this Review, we describe how HGT has shaped the web of life using examples of HGT among prokaryotes, between prokaryotes and eukaryotes, and even between multicellular eukaryotes. We discuss replacement and additive HGT, the proposed mechanisms of HGT, selective forces that influence HGT, and the evolutionary impact of HGT on ancestral populations and existing populations such as the human microbiome.

The biology of Trichomonas vaginalis in the light of urogenital tract infection

The human pathogen Trichomonas vaginalis is a parasitic protist. It is a representative of the eukaryotic supergroup Excavata that includes a few other protist parasites such as Leishmania, Trypanosoma and Giardia. T. vaginalis is the agent of trichomoniasis and in the US alone, one in 30 women tests positive for this parasite. The disease is easily treated with metronidazole in most cases, but resistant strains are on the rise. The biology of Trichomonas is remarkable: it includes for example the biggest protist genome currently sequenced, the expression of about 30,000 protein-encoding genes (and thousands of lncRNAs and pseudogenes), anaerobic hydrogenosomes, rapid morphogenesis during infection, the secretion of exosomes, the manipulation of the vaginal microbiota through phagocytosis and a rich strain-dependent diversity. Here we provide an overview of Trichomonas biology with a focus on its relevance for pathogenicity and summarise the most recent advances. With some respect this parasite offers the opportunity to serve as a model system to study certain aspects of cell and genome biology, but tackling the complex biology of T. vaginalis is also important to better understand the effects that accompany infection and direct symptoms.

Lateral gene transfers and the origins of the eukaryote proteome: a view from microbial parasites

Our knowledge of the extent and functional impact of lateral gene transfer (LGT) from prokaryotes to eukaryotes, outside of endosymbiosis, is still rather limited. Here we review the recent literature, focusing mainly on microbial parasites, indicating that LGT from diverse prokaryotes has played a significant role in the evolution of a number of lineages, and by extension throughout eukaryotic evolution. As might be expected, taxonomic biases for donor prokaryotes indicate that shared habitat is a major factor driving transfers. The LGTs identified predominantly affect enzymes from metabolic pathways, but over a third of LGT are genes for putative proteins of unknown function. Finally, we discuss the difficulties in analysing LGT among eukaryotes and suggest that high-throughput methodologies integrating different approaches are needed to achieve a more global understanding of the importance of LGT in eukaryotic evolution.