The not so universal tree of life or the place of viruses in the living world

Hazards of antiviral contamination in water: Dissemination, fate, risk and their impact on fish

Antiviral drugs are a cornerstone in the first line of antiviral therapy and their demand rises consistently with increments in viral infections and successive outbreaks. The drugs enter the waters due to improper disposal methods or via human excreta following their consumption; consequently, many of them are now classified as emerging pollutants. Hereby, we review the global dissemination of these medications throughout different water bodies and thoroughly investigate the associated risk they pose to the aquatic fauna, particularly our vertebrate relative fish, which has great economic and dietary importance and subsequently serves as a major doorway to the human exposome. Our risk assessment identifies eleven such drugs that presently pose high to moderate levels of risk to the fish. The antiviral drugs are likely to induce oxidative stress, alter the behaviour, affect different physiological processes and provoke various toxicological mechanisms. Many of the compounds exhibit elevated bioaccumulation potential, while, some have an increased tendency to leach through soil and contaminate the groundwater. Eight antiviral medications show a highly recalcitrant nature and would impact the aquatic life consistently in the long run and continue to influence the human exposome. Thereby, we call for urgent ecopharmacovigilance measures and modification of current water treatment methods.

Chapter 5: Major Biological Innovations in the History of Life on Earth

All organisms living on Earth descended from a single, common ancestral population of cells, known as LUCA-the last universal common ancestor. Since its emergence, the diversity and complexity of life have increased dramatically. This chapter focuses on four key biological innovations throughout Earth's history that had a significant impact on the expansion of phylogenetic diversity, organismal complexity, and ecospace habitation. First is the emergence of the last universal common ancestor, LUCA, which laid the foundation for all life-forms on Earth. Second is the evolution of oxygenic photosynthesis, which resulted in global geochemical and biological transformations. Third is the appearance of a new type of cell-the eukaryotic cell-which led to the origin of a new domain of life and the basis for complex multicellularity. Fourth is the multiple independent origins of multicellularity, resulting in the emergence of a new level of complex individuality. A discussion of these four key events will improve our understanding of the intertwined history of our planet and its inhabitants and better inform the extent to which we can expect life at different degrees of diversity and complexity elsewhere.

Four principles to establish a universal virus taxonomy

A universal taxonomy of viruses is essential for a comprehensive view of the virus world and for communicating the complicated evolutionary relationships among viruses. However, there are major differences in the conceptualisation and approaches to virus classification and nomenclature among virologists, clinicians, agronomists, and other interested parties. Here, we provide recommendations to guide the construction of a coherent and comprehensive virus taxonomy, based on expert scientific consensus. Firstly, assignments of viruses should be congruent with the best attainable reconstruction of their evolutionary histories, i.e., taxa should be monophyletic. This fundamental principle for classification of viruses is currently included in the International Committee on Taxonomy of Viruses (ICTV) code only for the rank of species. Secondly, phenotypic and ecological properties of viruses may inform, but not override, evolutionary relatedness in the placement of ranks. Thirdly, alternative classifications that consider phenotypic attributes, such as being vector-borne (e.g., "arboviruses"), infecting a certain type of host (e.g., "mycoviruses," "bacteriophages") or displaying specific pathogenicity (e.g., "human immunodeficiency viruses"), may serve important clinical and regulatory purposes but often create polyphyletic categories that do not reflect evolutionary relationships. Nevertheless, such classifications ought to be maintained if they serve the needs of specific communities or play a practical clinical or regulatory role. However, they should not be considered or called taxonomies. Finally, while an evolution-based framework enables viruses discovered by metagenomics to be incorporated into the ICTV taxonomy, there are essential requirements for quality control of the sequence data used for these assignments. Combined, these four principles will enable future development and expansion of virus taxonomy as the true evolutionary diversity of viruses becomes apparent.

Frequency and Content of the Last Fifty Years of Papers on Aristotle's Writings on Biological Phenomena

Aristotle is often named as the first zoologist or biologist because of his writings on animals. Although Aristotle's major intention in these books was to illustrate his ideas of how knowledge and understanding might advance, at least one modern biologist (C. Darwin) has recognized Aristotle's depth and breadth as being of surviving merit. Of greater surprise is the ongoing attention that his works continue to receive, including publications in contemporary scientific journals. This review identifies 38 peer-reviewed papers on various topics from Aristotle's biological writings that have been published during the last 50 years. These papers are described according to content (genetics, population biology, anatomy, brain, movement), specific creatures (fish, scorpions, elephants, insects, birds), publication outlet, distribution over the fifty year period surveyed, and visible trends in the topics studied. It is concluded that, in the highly-competitive field of peer-reviewed scientific publication and citation, Aristotle's biology continues to excite the interest of scientists and remains salient to modern science itself.

Virus finding tools: current solutions and limitations

MOTIVATION

The study of the Human Virome remains challenging nowadays. Viral metagenomics, through high-throughput sequencing data, is the best choice for virus discovery. The metagenomics approach is culture-independent and sequence-independent, helping search for either known or novel viruses. Though it is estimated that more than 40% of the viruses found in metagenomics analysis are not recognizable, we decided to analyze several tools to identify and discover viruses in RNA-seq samples.

RESULTS

We have analyzed eight Virus Tools for the identification of viruses in RNA-seq data. These tools were compared using a synthetic dataset of 30 viruses and a real one. Our analysis shows that no tool succeeds in recognizing all the viruses in the datasets. So we can conclude that each of these tools has pros and cons, and their choice depends on the application domain.

AVAILABILITY

Synthetic data used through the review and raw results of their analysis can be found at https://zenodo.org/record/6426147. FASTQ files of real data can be found in GEO (https://www.ncbi.nlm.nih.gov/gds) or ENA (https://www.ebi.ac.uk/ena/browser/home). Raw results of their analysis can be downloaded from https://zenodo.org/record/6425917.

Current Opinion in LAIV: A Matter of Parent Virus Choice

Influenza is still a frequent seasonal infection of the upper respiratory tract, which may have deadly consequences, especially for the elderly. This is in spite of the availability of vaccines suggested for persons above 65 years of age. Two types of conventional influenza vaccines are currently licensed for use-live attenuated and inactivated vaccines. Depending on local regulatory requirements, live attenuated vaccines are produced by the reverse genetics technique or by classical reassortment in embryonated chicken eggs. Sometimes, the efficiency of classical reassortment is complicated by certain properties of the wild-type parent virus. Cases of low efficacy of vaccines have been noted, which, among other reasons, may be associated with suboptimal properties of the wild-type parent virus that are not considered when recommendations for influenza vaccine composition are made. Unfortunately, knowledge surrounding the roles of properties of the circulating influenza virus and its impact on the efficacy of the reassortment process, vaccination efficiency, the infectivity of the vaccine candidates, etc., is now scattered in different publications. This review summarizes the main features of the influenza virus that may dramatically affect different aspects of the preparation of egg-derived live attenuated vaccine candidates and their effectiveness. The author expresses her personal view, which may not coincide with the opinion of other experts in the field of influenza vaccines.

Towards understanding mechanisms and functional consequences of bacterial interactions with members of various kingdoms in complex biofilms that abound in nature

The microbial world represents a phenomenal diversity of microorganisms from different kingdoms of life which occupy an impressive set of ecological niches. Most, if not all, microorganisms once colonise a surface develop architecturally complex surface-adhered communities which we refer to as biofilms. They are embedded in polymeric structural scaffolds serve as a dynamic milieu for intercellular communication through physical and chemical signalling. Deciphering microbial ecology of biofilms in various natural or engineered settings has revealed co-existence of microorganisms from all domains of life, including Bacteria, Archaea and Eukarya. The coexistence of these dynamic microbes is not arbitrary, as a highly coordinated architectural setup and physiological complexity show ecological interdependence and myriads of underlying interactions. In this review, we describe how species from different kingdoms interact in biofilms and discuss the functional consequences of such interactions. We highlight metabolic advances of collaboration among species from different kingdoms, and advocate that these interactions are of great importance and need to be addressed in future research. Since trans-kingdom biofilms impact diverse contexts, ranging from complicated infections to efficient growth of plants, future knowledge within this field will be beneficial for medical microbiology, biotechnology, and our general understanding of microbial life in nature.

Viruses Defined by the Position of the Virosphere within the Replicator Space

Originally, viruses were defined as miniscule infectious agents that passed through filters that retain even the smallest cells. Subsequently, viruses were considered obligate intracellular parasites whose reproduction depends on their cellular hosts for energy supply and molecular building blocks. However, these features are insufficient to unambiguously define viruses as they are broadly understood today. We outline possible approaches to define viruses and explore the boundaries of the virosphere within the virtual space of replicators and the relationships between viruses and other types of replicators. Regardless of how, exactly, viruses are defined, viruses clearly have evolved on many occasions from nonviral replicators, such as plasmids, by recruiting host proteins to become virion components. Conversely, other types of replicators have repeatedly evolved from viruses. Thus, the virosphere is a dynamic entity with extensive evolutionary traffic across its boundaries. We argue that the virosphere proper, here termed orthovirosphere, consists of a distinct variety of replicators that encode structural proteins encasing the replicators' genomes, thereby providing protection and facilitating transmission among hosts. Numerous and diverse replicators, such as virus-derived but capsidless RNA and DNA elements, or defective viruses occupy the zone surrounding the orthovirosphere in the virtual replicator space. We define this zone as the perivirosphere. Although intense debates on the nature of certain replicators that adorn the internal and external boundaries of the virosphere will likely continue, we present an operational definition of virus that recently has been accepted by the International Committee on Taxonomy of Viruses.

A Place for Viruses on the Tree of Life

Viruses are ubiquitous. They infect almost every species and are probably the most abundant biological entities on the planet, yet they are excluded from the Tree of Life (ToL). However, there can be no doubt that viruses play a significant role in evolution, the force that facilitates all life on Earth. Conceptually, viruses are regarded by many as non-living entities that hijack living cells in order to propagate. A strict separation between living and non-living entities places viruses far from the ToL, but this may be theoretically unsound. Advances in sequencing technology and comparative genomics have expanded our understanding of the evolutionary relationships between viruses and cellular organisms. Genomic and metagenomic data have revealed that co-evolution between viral and cellular genomes involves frequent horizontal gene transfer and the occasional co-option of novel functions over evolutionary time. From the giant, ameba-infecting marine viruses to the tiny Porcine circovirus harboring only two genes, viruses and their cellular hosts are ecologically and evolutionarily intertwined. When deciding how, if, and where viruses should be placed on the ToL, we should remember that the Tree functions best as a model of biological evolution on Earth, and it is important that models themselves evolve with our increasing understanding of biological systems.

A novel cypovirus found in a betabaculovirus co-infection context contains a poxvirus immune nuclease (poxin)-related gene

The cassava hornworm Erinnyis ello ello (Lepidoptera: Sphingidae) is an important pest in Brazil. This insect feeds on host plants of several species, especially Manihot esculenta (cassava) and Hevia brasiliensis (rubber tree). Cassava hornworm outbreaks are quite common in Brazil and can cause great impact over crop production. Granulare and polyhedral-shaped occlusion bodies (OBs) were observed in extracts of dead E. ello larvae from rubber-tree plantations by light and scanning electron microscopy (SEM), suggesting a mixed infection. The polyhedral-shaped OB surface revealed indentations that resemble those found in cypovirus polyhedra. After OB nucleic acid extraction followed by cDNA production and Illumina deep-sequencing analysis, the results confirmed for the presence of a putative novel cypovirus that carries ten segments and also a betabaculovirus (Erinnyis ello granulovirus, ErelGV). Phylogenetic analysis of the predicted segment 1-enconded RdRP showed that the new cypovirus isolate is closely related to a member of species Cypovirus 2, which was isolated from Inachis io (Lepidoptera: Nymphalidae). Therefore, we named this new isolate Erinnyis ello cypovirus 2 (ErelCPV-2). Genome in silico analyses showed that ErelCPV-2 segment 8 (S8) has a predicted amino acid identity of 35.82 % to a hypothetical protein of betabaculoviruses. This putative protein has a cGAMP-specific nuclease domain related to the poxvirus immune nucleases (poxins) from the 2',3'-cGAMP-degrading enzyme family.

A distinct lineage of Caudovirales that encodes a deeply branching multi-subunit RNA polymerase

Bacteriophages play critical roles in the biosphere, but their vast genomic diversity has obscured their evolutionary origins, and phylogenetic analyses have traditionally been hindered by their lack of universal phylogenetic marker genes. In this study we mine metagenomic data and identify a clade of Caudovirales that encodes the β and β' subunits of multi-subunit RNA polymerase (RNAP), a high-resolution phylogenetic marker which enables detailed evolutionary analyses. Our RNAP phylogeny revealed that the Caudovirales RNAP forms a clade distinct from cellular homologs, suggesting an ancient acquisition of this enzyme. Within these multimeric RNAP-encoding Caudovirales (mReC), we find that the similarity of major capsid proteins and terminase large subunits further suggests they form a distinct clade with common evolutionary origin. Our study characterizes a clade of RNAP-encoding Caudovirales and suggests the ancient origin of this enzyme in this group, underscoring the important role of viruses in the early evolution of life on Earth.

Huge bacteriophages: bridging the gap?

Huge bacteriophages display genome sizes that bridge the gap between viral and bacterial genomes. Large Pseudomonas phages elaborate a nucleus-like structure in the infected bacterial cell and a tubulin-like phage protein forms a kind of spindle apparatus. While this probably represents cases of convergent evolution, these observations revive the discussion on the origin of eukaryotic cells.

Giant Viruses-Big Surprises

Viruses are the most prevalent infectious agents, populating almost every ecosystem on earth. Most viruses carry only a handful of genes supporting their replication and the production of capsids. It came as a great surprise in 2003 when the first giant virus was discovered and found to have a >1 Mbp genome encoding almost a thousand proteins. Following this first discovery, dozens of giant virus strains across several viral families have been reported. Here, we provide an updated quantitative and qualitative view on giant viruses and elaborate on their shared and variable features. We review the complexity of giant viral proteomes, which include functions traditionally associated only with cellular organisms. These unprecedented functions include components of the translation machinery, DNA maintenance, and metabolic enzymes. We discuss the possible underlying evolutionary processes and mechanisms that might have shaped the diversity of giant viruses and their genomes, highlighting their remarkable capacity to hijack genes and genomic sequences from their hosts and environments. This leads us to examine prominent theories regarding the origin of giant viruses. Finally, we present the emerging ecological view of giant viruses, found across widespread habitats and ecological systems, with respect to the environment and human health.

Virus classification - where do you draw the line?

High-throughput sequencing (HTS) and its use in recovering and assembling novel virus sequences from environmental, human clinical, veterinary and plant samples has unearthed a vast new catalogue of viruses. Their classification, known by their sequences alone, sets a major challenge to traditional virus taxonomy, especially at the family and species levels, which have been historically based largely on descriptive taxon definitions. These typically entail some knowledge of their phenotypic properties, including replication strategies, virion structure and clinical and epidemiological features, such as host range, geographical distribution and disease outcomes. Little to no information on these attributes is available, however, for viruses identified in metagenomic datasets. If such viruses are to be included in virus taxonomy, their assignments will have to be guided largely or entirely by metrics of genetic relatedness. The immediate problem here is that the International Committee on Taxonomy of Viruses (ICTV), an organisation that authorises the taxonomic classification of viruses, provides little or no guidance on how similar or how divergent viruses must be in order to be considered members of new species or new families. We have recently developed a method for scoring genomic (dis)similarity between viruses (Genome Relationships Applied to Virus Taxonomy - GRAViTy) among the eukaryotic and prokaryotic viruses currently classified by the ICTV. At the family and genus levels, we found large-scale consistency between genetic relationships and their taxonomic assignments for eukaryotic viruses of all genome configurations and genome sizes. Family assignments of prokaryotic viruses have, however, been made at a quite different genetic level, and groupings currently classified as sub-families are a much better match to the eukaryotic virus family level. These findings support the ongoing reorganisation of bacteriophage taxonomy by the ICTV Phage Study Group. A rapid and objective means to explore metagenomic viral diversity and make evidence-based assignments for such viruses at each taxonomic layer is essential. Analysis of sequences by GRAViTy provides evidence that family (and genus) assignments of currently classified viruses are largely underpinned by genomic relatedness, and these features could serve as a guide towards an evidence-based classification of metagenomic viruses in the future.

Viral species, viral genomes and HIV vaccine design: is the rational design of biological complexity a utopia?

A common logical confusion is prevalent in the whole of biology, namely that biological species are viewed both as an abstract category in an hierarchical classification and as a concrete kind of organism. This is partly due to the fact that the vast majority of living organisms do not have common names that differ from the Latin name of the species to which the organism belongs. However, it is somewhat astonishing that the same confusion exists in virology since every virus has a common name, different from the species name to which the virus belongs, which could be used to refer to the infectious viral entity as a concrete material object. The original 1991 ICTV definition of virus species stated that a virus species is a polythetic class of viruses and thus that a species is a class, namely a conceptual construction of the mind and not a physical, real object located in space and time. In 2013, the ICTV redefined a virus species no longer as a class but as a material object consisting of a monophyletic group of viruses that were all physically part of the species. This new definition is reminiscent of an earlier school of thought known as bionominalism which considered species to be concrete individuals rather than classes. Both bionominalism and the new ICTV definition are based on the logical fallacy of reification which treats abstractions such as classes as if they were concrete physical entities. The implications of this new ontology of virus species for virus taxonomy and for the possibility of incorporating nucleotide metagenomic sequences in the current ICTV classification is discussed.

A clash of ideas - the varying uses of the 'species' term in virology and their utility for classifying viruses in metagenomic datasets

Species definitions of viruses are frequently descriptive, with assignments often being based on their disease manifestations, host range, geographical distribution and transmission routes. This method of categorizing viruses has recently been challenged by technology advances, such as high-throughput sequencing. These have dramatically increased knowledge of viral diversity in the wider environment that dwarfs the current catalogue of viruses classified by the International Committee for the Taxonomy of Viruses (ICTV). However, because such viruses are known only from their sequences without phenotypic information, it is unclear how they might be classified consistently with much of the existing taxonomy framework. This difficulty exposes deeper incompatibilities in how species are conceptualized. The original species assignments based on disease or other biological attributes were primarily descriptive, similar to principles used elsewhere in biology for species taxonomies. In contrast, purely sequence-based classifications rely on genetic metrics such as divergence thresholds that include or exclude viruses in individual species categories. These different approaches bring different preconceptions about the nature of a virus species, the former being more easily conceptualized as a category with a part/whole relationship of individuals and species, while species defined by divergence thresholds or other genetic metrics are essentially logically defined groups with specific inclusion and exclusion criteria. While descriptive species definitions match our intuitive division of viruses into natural kinds, rules-based genetic classifications are required for viruses known from sequence alone, whose incorporation into the ICTV taxonomy is essential if it is to represent the true diversity of viruses in nature.

Does the discovery of the mimivirus call into question attempts to define life?

Despite biology being ‘The study of living organisms’ (Proffitt, 2017), there is no consensus between biologists on the definition of life (Bedau, 2010). Defining life has challenged and divided biologists and philosophers alike ever since Aristotle proposed the first definition. Emerging fields like synthetic biology and exobiology have rekindled attempts at establishing a definition of life for practical purposes. The question presents many challenges with each attempt thus far leading to unintended implications and strong counterexamples. It is an inherently multidisciplinary challenge with each approach giving wildly varying and often irreconcilable definitions. The given definitions of life are numerous with over 300 definitions published in books and journals. The unique characteristics of the mimivirus, discovered in 2003, and later giant viruses, rekindled the discussion in defining life, indicating other complications in a definition.

Aggregation/dispersion transitions of T4 phage triggered by environmental ion availability

Background

Bacteriophage survives in at least two extremes of ionic environments: bacterial host (high ionic-cytosol) and that of soil (low ionic-environmental water). The impact of ionic composition in the micro- and macro-environments has not so far been addressed in phage biology.

Results

Here, we discovered a novel mechanism of aggregation/disaggregation transitions by phage virions. When normal sodium levels in phage media (150 mM) were lowered to 10 mM, advanced imaging by scanning electron microscopy, atomic force microscopy and dynamic light scattering all revealed formation of viral packages, each containing 20–100 virions. When ionic strength was returned from low to high, the aggregated state of phage reversed to a dispersed state, and the change in ionic strength did not substantially affect infectivity of the phage. By providing the direct evidence, that lowering of the sodium ion below the threshold of 20 mM causes rapid aggregation of phage while returning Na⁺ concentration to the values above this threshold causes dispersion of phage, we identified a biophysical mechanism of phage aggregation.

Conclusions

Our results implicate operation of group behavior in phage and suggest a new kind of quorum sensing among its virions that is mediated by ions. Loss of ionic strength may act as a trigger in an evolutionary mechanism to improve the survival of bacteriophage by stimulating aggregation of phage when outside a bacterial host. Reversal of phage aggregation is also a promising breakthrough in biotechnological applications, since we demonstrated here the ability to retain viable virion aggregates on standard micro-filters.

Isolation and Genome Sequencing of a Novel Pseudoalteromonas Phage PH1

The family Pseudoalteromonas is highly adaptable to dissimilar ecological habitats and plays an important ecological role in the marine environment. In this study, a new Pseudoalteromonas phage PH1 was isolated from the Yellow Sea. To better understand the bacteriophage, its biological properties, including morphology, host range, growth phenotype, thermal and pH stability, and nucleic acid composition, were investigated in detail. The result showed that the phage PH1 is a Podoviridae-phage with an icosahedral head (60 nm of diameter) and a short tail (26 nm in length). The phage PH1 genome consists of 42,685 bp length double-stranded DNA with a G+C content of 42.24% and is predicted to have 55 open reading frames (ORFs) with an average length of 740 bp nucleotides each. The phage PH1 genome adds a new Podoviridae-phage genome to marine bacteriophage dataset, which will provide useful basic information for further molecular research on interaction mechanisms between bacteriophages and their hosts.

Eukaryotic association module in phage WO genomes from Wolbachia

Viruses are trifurcated into eukaryotic, archaeal and bacterial categories. This domain-specific ecology underscores why eukaryotic viruses typically co-opt eukaryotic genes and bacteriophages commonly harbour bacterial genes. However, the presence of bacteriophages in obligate intracellular bacteria of eukaryotes may promote DNA transfers between eukaryotes and bacteriophages. Here we report a metagenomic analysis of purified bacteriophage WO particles of Wolbachia and uncover a eukaryotic association module in the complete WO genome. It harbours predicted domains, such as the black widow latrotoxin C-terminal domain, that are uninterrupted in bacteriophage genomes, enriched with eukaryotic protease cleavage sites and combined with additional domains to forge one of the largest bacteriophage genes to date (14,256 bp). To the best of our knowledge, these eukaryotic-like domains have never before been reported in packaged bacteriophages and their phylogeny, distribution and sequence diversity imply lateral transfers between bacteriophage/prophage and animal genomes. Finally, the WO genome sequences and identification of attachment sites will potentially advance genetic manipulation of Wolbachia.

Viruses commonly exchange genetic material with their hosts, but not with species from other domains of life. Here, the authors find that the bacteriophage WO of Wolbachia contains eukaryotic-like genes, implicating lateral genetic transfer between eukaryotes and viruses infecting bacteria.

To be or not to be alive: How recent discoveries challenge the traditional definitions of viruses and life

Three major discoveries have recently profoundly modified our perception of the viral world: molecular ecologists have shown that viral particles are more abundant than cells in natural environments; structural biologists have shown that some viruses from the three domains of life, Bacteria, Eukarya and Archaea, are evolutionarily related, and microbiologists have discovered giant viruses that rival with cells in terms of size and gene content. I discuss here the scientific and philosophical impact of these discoveries on the debates over the definition, nature (living or not), and origin of viruses. I suggest that viruses have often been considered non-living, because they are traditionally assimilated to their virions. However, the term virus describes a biological process and should integrate all aspects of the viral reproduction cycle. It is especially important to focus on the intracellular part of this cycle, the virocell, when viral information is actively expressed and reproduced, allowing the emergence of new viral genes. The virocell concept theoretically removes roadblocks that prevent defining viruses as living organisms. However, defining a "living organism" remains challenging, as indicated by the case of organelles that evolved from intracellular bacteria. To bypass this problem, I suggest considering that all biological entities that actively participate in the process of life are living.

Genomic signatures in viral sequences by in-frame and out-frame mutual information

In order to understand the unique biology of viruses, we use the Mutual Information Function (MIF) to characterize 792 viral sequences comprising 458 viral whole genomes. A 3-base periodicity (3-bp) was observed only in DNA-viruses whereas RNA-viruses showed irregular patterns. The correlation of MIF values at frequencies of 3-bp (in-frame) with frequencies of 4 and 5bps (out-frame), turned out to be useful to distinguish viruses according to their respective taxonomic order, and whether they pertain to any of the three different kingdoms, Eubacteria, Archaea and Eukarya. The clustering of viruses was carried out by the use of a new statistics, namely, the pair of in- and out-frame values of the MIF. The clustering thus obtained turned out to be entirely consistent with the current viral taxonomy. As a result we were able to compare in a single plot both viral and cellular genomes unlike any given phylogenetic reconstruction.

Functional and Evolutionary Characterization of a Gene Transfer Agent's Multilocus "Genome"

Gene transfer agents (GTAs) are phage-like particles that can package and transfer a random piece of the producing cell’s genome, but are unable to transfer all the genes required for their own production. As such, GTAs represent an evolutionary conundrum: are they selfish genetic elements propagating through an unknown mechanism, defective viruses, or viral structures “repurposed” by cells for gene exchange, as their name implies? In Rhodobacter capsulatus, production of the R. capsulatus GTA (RcGTA) particles is associated with a cluster of genes resembling a small prophage. Utilizing transcriptomic, genetic and biochemical approaches, we report that the RcGTA “genome” consists of at least 24 genes distributed across five distinct loci. We demonstrate that, of these additional loci, two are involved in cell recognition and binding and one in the production and maturation of RcGTA particles. The five RcGTA “genome” loci are widespread within Rhodobacterales, but not all loci have the same evolutionary histories. Specifically, two of the loci have been subject to frequent, probably virus-mediated, gene transfer events. We argue that it is unlikely that RcGTA is a selfish genetic element. Instead, our findings are compatible with the scenario that RcGTA is a virus-derived element maintained by the producing organism due to a selective advantage of within-population gene exchange. The modularity of the RcGTA “genome” is presumably a result of selection on the host organism to retain GTA functionality.

Horizontal transfer - imperative mission of acellular life forms, Acytota

Acytota is a kingdom of life covering satellites, plasmids, transposable elements, viroids and viruses, all outside the conventional tree of life but satisfying most life definitions. This review focuses on some aspects of Acytota, their "genomes" and life styles, the dominance of transposable elements and their evolutionary influence on other life forms in order to vindicate the Acytota as a life kingdom no more polyphyletic than other kingdoms and its members no more parasitic than other life forms.

Giant viruses: enfants terribles in the microbal world

ABSTRACT 

In the past decade knowledge about Megaviruses, also denoted as nucleocytoplasmic large DNA viruses (NCLDVs) has been growing quickly. In the current paper, we present a general description of NCLDVs including their genome size, gene functions and homologies to other forms of life and viruses. Evolution of giant viruses from the fourth domain of life (now extinct) and a genomic complexification from smaller DNA viruses are described. Undeniable is the fact that Megaviruses in terms of their size and genomic capacity belong in between cellular and viral worlds breaking several ‘viral dogmas.’ The host range of NCLDVs goes far beyond unicellular organisms and a major challenge in the future is to establish their pathogenicity in human population.

When Competing Viruses Unify: Evolution, Conservation, and Plasticity of Genetic Identities

In the early 1970s, Manfred Eigen and colleagues developed the quasispecies model (qs) for the population-based origin of RNAs representing the early genetic code. The Eigen idea is basically that a halo of mutants is generated by error-prone replication around the master fittest type which will behave similarly as a biological population. But almost from the start, very interesting and unexpected observations were made regarding competition versus co-operation which suggested more complex interactions. It thus became increasingly clear that although viruses functioned similar to biological species, their behavior was much more complex than the original theory could explain, especially adaptation without changing the consensus involving minority populations. With respect to the origin of natural codes, meaning, and code-use in interactions (communication), it also became clear that individual fittest type-based mechanisms were likewise unable to explain the origin of natural codes such as the genetic code with their context- and consortia-dependence (pragmatic nature). This, instead, required the participation of groups of agents competent in the code and able to edit code because natural codes do not code themselves. Three lines of inquiry, experimental virology, quasispecies theory, and the study of natural codes converged to indicate that consortia of co-operative RNA agents such as viruses must be involved in the fitness of RNA and its involvement in communication, i.e., code-competent interactions. We called this co-operative form quasispecies consortia (qs-c). They are the essential agents that constitute the possibility of evolution of biological group identity. Finally, the basic interactional motifs for the emergence of group identity, communication, and co-operation-together with its opposing functions-are explained by the "Gangen" hypothesis.

Absence of lysogeny in wild populations of Erwinia amylovora and Pantoea agglomerans

Lytic bacteriophages are in development as biological control agents for the prevention of fire blight disease caused by Erwinia amylovora. Temperate phages should be excluded as biologicals since lysogeny produces the dual risks of host resistance to phage attack and the transduction of virulence determinants between bacteria. The extent of lysogeny was estimated in wild populations of E. amylovora and Pantoea agglomerans with real-time polymerase chain reaction primers developed to detect E. amylovora phages belonging to the Myoviridae and Podoviridae families. Pantoea agglomerans, an orchard epiphyte, is easily infected by Erwinia spp. phages, and it serves as a carrier in the development of the phage-mediated biological control agent. Screening of 161 E. amylovora isolates from 16 distinct geographical areas in North America, Europe, North Africa and New Zealand and 82 P. agglomerans isolates from southern Ontario, Canada showed that none possessed prophage. Unstable phage resistant clones or lysogens were produced under laboratory conditions. Additionally, a stable lysogen was recovered from infection of bacterial isolate Ea110R with Podoviridae phage ΦEa35-20. These laboratory observations suggested that while lysogeny is possible in E. amylovora, it is rare or absent in natural populations, and there is a minimal risk associated with lysogenic conversion and transduction by Erwinia spp. phages.

Gene acquisition convergence between entomopoxviruses and baculoviruses

Organisms from diverse phylogenetic origins can thrive within the same ecological niches. They might be induced to evolve convergent adaptations in response to a similar landscape of selective pressures. Their genomes should bear the signature of this process. The study of unrelated virus lineages infecting the same host panels guarantees a clear identification of phyletically independent convergent adaptation. Here, we investigate the evolutionary history of genes in the accessory genome shared by unrelated insect large dsDNA viruses: the entomopoxviruses (EPVs, Poxviridae) and the baculoviruses (BVs). EPVs and BVs have overlapping ecological niches and have independently evolved similar infection processes. They are, in theory, subjected to the same selective pressures from their host’s immune responses. Their accessory genomes might, therefore, bear analogous genomic signatures of convergent adaption and could point out key genomic mechanisms of adaptation hitherto undetected in viruses. We uncovered 32 homologous, yet independent acquisitions of genes originating from insect hosts, different eukaryotes, bacteria and viruses. We showed different evolutionary levels of gene acquisition convergence in these viruses, underlining a continuous evolutionary process. We found both recent and ancient gene acquisitions possibly involved to the adaptation to both specific and distantly related hosts. Multidirectional and multipartite gene exchange networks appear to constantly drive exogenous gene assimilations, bringing key adaptive innovations and shaping the life histories of large DNA viruses. This evolutionary process might lead to genome level adaptive convergence.

Genomic characteristics and environmental distributions of the uncultivated Far-T4 phages

Viral metagenomics (viromics) is a tremendous tool to reveal viral taxonomic and functional diversity across ecosystems ranging from the human gut to the world's oceans. As with microbes however, there appear vast swaths of “dark matter” yet to be documented for viruses, even among relatively well-studied viral types. Here, we use viromics to explore the “Far-T4 phages” sequence space, a neighbor clade from the well-studied T4-like phages that was first detected through PCR study in seawater and subsequently identified in freshwater lakes through 454-sequenced viromes. To advance the description of these viruses beyond this single marker gene, we explore Far-T4 genome fragments assembled from two deeply-sequenced freshwater viromes. Single gene phylogenetic trees confirm that the Far-T4 phages are divergent from the T4-like phages, genome fragments reveal largely collinear genome organizations, and both data led to the delineation of five Far-T4 clades. Three-dimensional models of major capsid proteins are consistent with a T4-like structure, and highlight a highly conserved core flanked by variable insertions. Finally, we contextualize these now better characterized Far-T4 phages by re-analyzing 196 previously published viromes. These suggest that Far-T4 are common in freshwater and seawater as only four of 82 aquatic viromes lacked Far-T4-like sequences. Variability in representation across the five newly identified clades suggests clade-specific niche differentiation may be occurring across the different biomes, though the underlying mechanism remains unidentified. While complete genome assembly from complex communities and the lack of host linkage information still bottleneck virus discovery through viromes, these findings exemplify the power of metagenomics approaches to assess the diversity, evolutionary history, and genomic characteristics of novel uncultivated phages.

Defending definitions of life

Over the past 10 years, it has become unpopular to talk about definitions of life, under the assumption that attempts at a precise definition are counterproductive. Recent attempts have failed to meet strict philosophical criteria for definitions and have failed to reach consensus. I argue that provisional definitions are necessary for clear communications. Our current knowledge of biology justifies a number of universal claims about the category of life. Whether or not "life" represents a natural category, it maps to a number of important, observable processes. Given the importance of those processes and the extent of our knowledge, plural explicit definitions of life (and related categories) will be necessary for progress in astrobiology and origin-of-life studies as well as biology in general. I propose concrete categories related to, but not necessarily coextensive with, life for clear communication and hypothesis formation: Woese life, Darwin life, Haldane life.

Goods-thinking vs. tree-thinking: Finding a place for mobile genetic elements

While it has become increasingly clear that the Tree of Life hypothesis has limitations in its ability to describe the evolution of all evolving entities on the planet, there has been a marked reluctance to move away from the tree-based language. Ironically, while modifying the idea of the Tree of Life to the extent that it is only very distantly related to its original descriptions, there has been a very careful attempt to retain the language of tree-thinking. The recent movement away from a tree-thinking language toward a goods-thinking language and perspective is a significant improvement. In this commentary, we describe how goods-thinking can provide better descriptions of evolution, can integrate evolution with environment more closely and can offer an equal place for Mobile Genetic Elements and chromosomal elements in discussions of evolutionary history.

Phages in nature

Bacteriophages or phages are the most abundant organisms in the biosphere and they are a ubiquitous feature of prokaryotic existence. A bacteriophage is a virus which infects a bacterium. Archaea are also infected by viruses, whether these should be referred to as 'phages' is debatable, but they are included as such in the scope this article. Phages have been of interest to scientists as tools to understand fundamental molecular biology, as vectors of horizontal gene transfer and drivers of bacterial evolution, as sources of diagnostic and genetic tools and as novel therapeutic agents. Unraveling the biology of phages and their relationship with their hosts is key to understanding microbial systems and their exploitation. In this article we describe the roles of phages in different host systems and show how modeling, microscopy, isolation, genomic and metagenomic based approaches have come together to provide unparalleled insights into these small but vital constituents of the microbial world.

Cellular domains and viral lineages

It has been claimed that giant DNA viruses represent a separate, fourth domain of life in addition to the domains of Bacteria, Archaea, and Eukarya. Such classification disregards fundamental differences between the two types of living entities - viruses and cells - and results in confusion and controversies in evolutionary scenarios. We highlight these problems and emphasize the importance of restricting the term 'domain' to the descendants of the last universal cellular ancestor (LUCA), based on the shared ribosome structure. We suggest tracing phylogeny of viruses along evolutionary lineages primarily defined by virion architectures and the structures of the major capsid proteins.

Bacteriophage behavioral ecology: How phages alter their bacterial host's habits

Bacteriophages have an essential gene kit that enables their invasion, replication, and production. In addition to this "core" genome, they can carry "accessory" genes that dramatically impact bacterial biology, and presumably boost their own success. The content of phage genomes continue to surprise us by revealing new ways that viruses impact bacterial biology. The genome of a Clostridium difficile myovirus, phiCDHM1, contains homologs of three bacterial accessory gene regulator (agr) genes. The agr system is a type of quorum sensing (QS), via which the phage may modify C. difficile interactions with its environment. Although their mechanism of action is unknown, mutants in bacterial versions of these genes impact sporulation and virulence. To explore how phage QS genes may influence C. difficile biology, we examine the main categories of bacterial behavior that phages have been shown to influence and discuss how interactions via QS could influence behavior at a wider level.

Modeling the infection dynamics of bacteriophages in enteric Escherichia coli: estimating the contribution of transduction to antimicrobial gene spread

Animal-associated bacterial communities are infected by bacteriophages, although the dynamics of these infections are poorly understood. Transduction by bacteriophages may contribute to transfer of antimicrobial resistance genes, but the relative importance of transduction among other gene transfer mechanisms is unknown. We therefore developed a candidate deterministic mathematical model of the infection dynamics of enteric coliphages in commensal Escherichia coli in the large intestine of cattle. We assumed the phages were associated with the intestine and were predominantly temperate. Model simulations demonstrated how, given the bacterial ecology and infection dynamics, most (>90%) commensal enteric E. coli bacteria may become lysogens of enteric coliphages during intestinal transit. Using the model and the most liberal assumptions about transduction efficiency and resistance gene frequency, we approximated the upper numerical limits ("worst-case scenario") of gene transfer through specialized and generalized transduction in E. coli by enteric coliphages when the transduced genetic segment is picked at random. The estimates were consistent with a relatively small contribution of transduction to lateral gene spread; for example, generalized transduction delivered the chromosomal resistance gene to up to 8 E. coli bacteria/hour within the population of 1.47 × 10(8) E. coli bacteria/liter luminal contents. In comparison, the plasmidic blaCMY-2 gene carried by ~2% of enteric E. coli was transferred by conjugation at a rate at least 1.4 × 10(3) times greater than our generalized transduction estimate. The estimated numbers of transductants varied nonlinearly depending on the ecology of bacteria available for phages to infect, that is, on the assumed rates of turnover and replication of enteric E. coli.

[The great virus comeback]

Viruses have been considered for a long time as by-products of biological evolution. This view is changing now as a result of several recent discoveries. Viral ecologists have shown that viral particles are the most abundant biological entities on our planet, whereas metagenomic analyses have revealed an unexpected abundance and diversity of viral genes in the biosphere. Comparative genomics have highlighted the uniqueness of viral sequences, in contradiction with the traditional view of viruses as pickpockets of cellular genes. On the contrary, cellular genomes, especially eukaryotic ones, turned out to be full of genes derived from viruses or related elements (plasmids, transposons, retroelements and so on). The discovery of unusual viruses infecting archaea has shown that the viral world is much more diverse than previously thought, ruining the traditional dichotomy between bacteriophages and viruses. Finally, the discovery of giant viruses has blurred the traditional image of viruses as small entities. Furthermore, essential clues on virus history have been obtained in the last ten years. In particular, structural analyses of capsid proteins have uncovered deeply rooted homologies between viruses infecting different cellular domains, suggesting that viruses originated before the last universal common ancestor (LUCA). These studies have shown that several lineages of viruses originated independently, i.e., viruses are polyphyletic. From the time of LUCA, viruses have coevolved with their hosts, and viral lineages can be viewed as lianas wrapping around the trunk, branches and leaves of the tree of life. Although viruses are very diverse, with genomes encoding from one to more than one thousand proteins, they can all be simply defined as organisms producing virions. Virions themselves can be defined as infectious particles made of at least one protein associated with the viral nucleic acid, endowed with the capability to protect the viral genome and ensure its delivery to the infected cell. These definitions, which clearly distinguish viruses from plasmids, suggest that infectious RNA molecules that only encode an RNA replicase presently classified among viruses by the ICTV (International Committee for the Taxonomy of Viruses) into families of Endornaviridae and Hypoviridae are in fact RNA plasmids. Since a viral genome should encode for at least one structural protein, these definitions also imply that viruses originated after the emergence of the ribosome in an RNA-protein cellular world. Although virions are the hallmarks of viruses, viruses and virions should not be confused. The infection transforms the ribocell (cell encoding ribosomes and dividing by binary fission) into a virocell (cell producing virions) or ribovirocell (cell that produces virions but can still divide by binary fission). In the ribovirocell, two different organisms, defined by their distinct evolutionary histories, coexist in symbiosis in the same cell. The virocells or ribovirocells are the living forms of the virus, which can be in fine considered to be a living organism. In the virocell, the metabolism is reorganized for the production of virions, while the ability to capture and store free energy is retained, as in other cellular organisms. In the virocell, viral genomes replicate, recombine and evolve, leading to the emergence of new viral proteins and potentially novel functions. Some of these new functions can be later on transferred to the cell, explaining how viruses can play a major (often underestimated) role in the evolution of cellular organisms. The virocell concept thus helps to understand recent hypotheses suggesting that viruses played a critical role in major evolutionary transitions, such as the origin of DNA genomes or else the origin of the eukaryotic nucleus. Finally, it is more and more recognized that viruses are the major source of variation and selection in living organisms (both viruses and cells), the two pillars of darwinism. One can thus conclude that the continuous interaction between viruses and cells, all along the history of life, has been, and still is, a major engine of biological evolution.

The major role of viruses in cellular evolution: facts and hypotheses

Viral particles are much more abundant than cells and viral genes outnumber cellular ones in the biosphere. Cellular genomes also harbour many integrated viruses whereas cellular genes are rare in viral genomes. The gene flux from virus to cell is thus overwhelming if compared with the opposite event. Novel viral genes continuously arose during replication/recombination of viral genomes in the virocell. These genes can become 'cellular genes' when viral genomes integrate into cellular ones. Together with the arm race between viruses and cells, this explains why viruses have played a major role in shaping cellular gene contents. Several documented cases show that viruses have been involved in the emergence of evolutionary innovations. This gives credit to hypotheses suggesting that viruses have played an important role in the formation of modern cells.

EGN: a wizard for construction of gene and genome similarity networks

Background

Increasingly, similarity networks are being used for evolutionary analyses of molecular datasets. These networks are very useful, in particular for the analysis of gene sharing, lateral gene transfer and for the detection of distant homologs. Currently, such analyses require some computer programming skills due to the limited availability of user-friendly freely distributed software. Consequently, although appealing, the construction and analyses of these networks remain less familiar to biologists than do phylogenetic approaches.

Results

In order to ease the use of similarity networks in the community of evolutionary biologists, we introduce a software program, EGN, that runs under Linux or MacOSX. EGN automates the reconstruction of gene and genome networks from nucleic and proteic sequences. EGN also implements statistics describing genetic diversity in these samples, for various user-defined thresholds of similarities. In the interest of studying the complexity of evolutionary processes affecting microbial evolution, we applied EGN to a dataset of 571,044 proteic sequences from the three domains of life and from mobile elements. We observed that, in Borrelia, plasmids play a different role than in most other eubacteria. Rather than being genetic couriers involved in lateral gene transfer, Borrelia’s plasmids and their genes act as private genetic goods, that contribute to the creation of genetic diversity within their parasitic hosts.

Conclusion

EGN can be used for constructing, analyzing, and mining molecular datasets in evolutionary studies. The program can help increase our knowledge of the processes through which genes from distinct sources and/or from multiple genomes co-evolve in lineages of cellular organisms.

Bacteriophage electron microscopy

Since the advent of the electron microscope approximately 70 years ago, bacterial viruses and electron microscopy are inextricably linked. Electron microscopy proved that bacteriophages are particulate and viral in nature, are complex in size and shape, and have intracellular development cycles and assembly pathways. The principal contribution of electron microscopy to bacteriophage research is the technique of negative staining. Over 5500 bacterial viruses have so far been characterized by electron microscopy, making bacteriophages, at least on paper, the largest viral group in existence. Other notable contributions are cryoelectron microcopy and three-dimensional image reconstruction, particle counting, and immunoelectron microscopy. Scanning electron microscopy has had relatively little impact. Transmission electron microscopy has provided the basis for the recognition and establishment of bacteriophage families and is one of the essential criteria to classify novel viruses into families. It allows for instant diagnosis and is thus the fastest diagnostic technique in virology. The most recent major contribution of electron microscopy is the demonstration that the capsid of tailed phages is monophyletic in origin and that structural links exist between some bacteriophages and viruses of vertebrates and archaea. DNA sequencing cannot replace electron microscopy and vice versa.

Fake virus particles generated by fluorescence microscopy

Many laboratories are actively studying the abundance and roles of viruses in natural ecosystems. In these studies, the presence and number of viral particles is usually determined using fluorescent dyes. However, DNA associated with membrane-derived vesicles (MVs), gene transfer agents (GTAs), or cell debris can produce fluorescent dots that can be confused with viral particles. We suspect that fluorescence counting can lead to overestimation of virus numbers and even suggest the presence of viruses when there are none. Future studies in environmental virology should acknowledge this point and consider how to bypass this problem. Besides trying to improve discrimination between virions and MVs, we suggest adopting less holistic approaches, focusing on the detection of known virus groups and the isolation of new viruses from a broader range of hosts.

Abstract profiles of structural stability point to universal tendencies, family-specific factors, and ancient connections between languages

Language is the best example of a cultural evolutionary system, able to retain a phylogenetic signal over many thousands of years. The temporal stability (conservatism) of basic vocabulary is relatively well understood, but the stability of the structural properties of language (phonology, morphology, syntax) is still unclear. Here we report an extensive Bayesian phylogenetic investigation of the structural stability of numerous features across many language families and we introduce a novel method for analyzing the relationships between the "stability profiles" of language families. We found that there is a strong universal component across language families, suggesting the existence of universal linguistic, cognitive and genetic constraints. Against this background, however, each language family has a distinct stability profile, and these profiles cluster by geographic area and likely deep genealogical relationships. These stability profiles seem to show, for example, the ancient historical relationships between the Siberian and American language families, presumed to be separated by at least 12,000 years, and possible connections between the Eurasian families. We also found preliminary support for the punctuated evolution of structural features of language across families, types of features and geographic areas. Thus, such higher-level properties of language seen as an evolutionary system might allow the investigation of ancient connections between languages and shed light on the peopling of the world.

Darwin's goldmine is still open: variation and selection run the world

The scientific contribution of Darwin, still agonized in many religious circles, has now been recognized and celebrated by scientists from various disciplines. However, in recent years, several evolutionists have criticized Darwin as outdated, arguing that "Darwinism," assimilated to the "tree of life," cannot explain microbial evolution, or else was not operating in early life evolution. These critics either confuse "Darwinism" and old versions of "neo-Darwinism" or misunderstand the role of gene transfers in evolution. The core of Darwin explanation of evolution (variation/selection) remains necessary and sufficient to decipher the history of life. The enormous diversity of mechanisms underlying variations has been successfully interpreted by evolutionists in this framework and has considerably enriched the corpus of evolutionary biology without the necessity to kill the father. However, it remains for evolutionists to acknowledge interactions between cells and viruses (unknown for Darwin) as a major driving force in life evolution.

Metagenomics and future perspectives in virus discovery

Monitoring the emergence and re-emergence of viral diseases with the goal of containing the spread of viral agents requires both adequate preparedness and quick response. Identifying the causative agent of a new epidemic is one of the most important steps for effective response to disease outbreaks. Traditionally, virus discovery required propagation of the virus in cell culture, a proven technique responsible for the identification of the vast majority of viruses known to date. However, many viruses cannot be easily propagated in cell culture, thus limiting our knowledge of viruses. Viral metagenomic analyses of environmental samples suggest that the field of virology has explored less than 1% of the extant viral diversity. In the last decade, the culture-independent and sequence-independent metagenomic approach has permitted the discovery of many viruses in a wide range of samples. Phylogenetically, some of these viruses are distantly related to previously discovered viruses. In addition, 60-99% of the sequences generated in different viral metagenomic studies are not homologous to known viruses. In this review, we discuss the advances in the area of viral metagenomics during the last decade and their relevance to virus discovery, clinical microbiology and public health. We discuss the potential of metagenomics for characterization of the normal viral population in a healthy community and identification of viruses that could pose a threat to humans through zoonosis. In addition, we propose a new model of the Koch's postulates named the 'Metagenomic Koch's Postulates'. Unlike the original Koch's postulates and the Molecular Koch's postulates as formulated by Falkow, the metagenomic Koch's postulates focus on the identification of metagenomic traits in disease cases. The metagenomic traits that can be traced after healthy individuals have been exposed to the source of the suspected pathogen.

Philosophy and evolution: minding the gap between evolutionary patterns and tree-like patterns

Ever since Darwin, the familiar genealogical pattern known as the Tree of Life (TOL) has been prominent in evolutionary thinking and has dominated not only systematics, but also the analysis of the units of evolution. However, recent findings indicate that the evolution of DNA, especially in prokaryotes and such DNA vehicles as viruses and plasmids, does not follow a unique tree-like pattern. Because evolutionary patterns track a greater range of processes than those captured in genealogies, genealogical patterns are in fact only a subset of a broader set of evolutionary patterns. This fact suggests that evolutionists who focus exclusively on genealogical patterns are blocked from providing a significant range of genuine evolutionary explanations. Consequently, we highlight challenges to tree-based approaches, and point the way toward more appropriate methods to study evolution (although we do not present them in technical detail). We argue that there is significant benefit in adopting wider range of models, evolutionary representations, and evolutionary explanations, based on an analysis of the full range of evolutionary processes. We introduce an ecosystem orientation into evolutionary thinking that highlights the importance of "type 1 coalitions" (functionally related units with genetic exchanges, aka "friends with genetic benefits"), "type 2 coalitions" (functionally related units without genetic exchanges), "communal interactions," and "emergent evolutionary properties." On this basis, we seek to promote the study of (especially prokaryotic) evolution with dynamic evolutionary networks, which are less constrained than the TOL, and to provide new ways to analyze an expanded range of evolutionary units (genetic modules, recombined genes, plasmids, phages and prokaryotic genomes, pangenomes, microbial communities) and evolutionary processes. Finally, we discuss some of the conceptual and practical questions raised by such network-based representation.