Marine T4-type bacteriophages, a ubiquitous component of the dark matter of the biosphere

Isolation, characterization, and genomic analysis of phage MY02 targeting extended-spectrum beta-lactamase-producing Klebsiella pneumoniae

Abuse of antibiotics has led to increased rates of resistance in extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae and an acceleration in the emergence of drug-resistant strains, which can have serious consequences for nosocomial infections. In this study, phage MY02, which infects ESBL-producing Klebsiella pneumoniae, was isolated from sewage and characterized. Phage MY02 was found to have an optimal multiplicity of infection of 0.001, with a lysis period of up to 40 minutes and an average burst of about 80 plaque-forming units per cell. The phage was found to be stable over a temperature range of -20 to 60°C and a pH range of 3-11 and to have a broad host range. Whole-genome sequencing showed that the genome of phage MY02 is ??171,821?? bp in length and contains 293 open reading frames. Sequence comparisons and phylogenetic analysis showed that phage MY02 belongs to the genus Marfavirus in the class Caudoviricetes. This novel broad-spectrum Klebsiella pneumoniae phage has potential applications against bacterial infections.

New Bacteriophage Pseudomonas Phage Ka2 from a Tributary Stream of Lake Baikal

Pseudomonas aeruginosa, an opportunistic pathogen, causes various biofilm-associated infections like pneumonia, infections in cystic fibrosis patients, and urinary tract and burn infections with high morbidity and mortality, as well as low treatment efficacy due to the extremely wide spread of isolates with multidrug resistance. Here, we report the new bacteriophage Pseudomonas phage Ka2 isolated from a tributary stream of Lake Baikal and belonging to the Pbunavirus genus. Transmission electron microscopy resolved that Pseudomonas phage Ka2 has a capsid of 57 ± 9 nm and a contractile and inflexible tail of 115 ± 10 nm in the non-contracted state. The genome consists of 66,310 bp with a GC content of 55% and contains 96 coding sequences. Among them, 52 encode proteins have known functions, and none of them are potentially associated with lysogeny. The bacteriophage lyses 21 of 30 P. aeruginosa clinical isolates and decreases the MIC of amikacin, gentamicin, and cefepime up to 16-fold and the MIC of colistin up to 32-fold. When treating the biofilms with Ka2, the biomass was reduced by twice, and up to a 32-fold decrease in the antibiotics MBC against biofilm-embedded cells was achieved by the combination of Ka2 with cefepime for the PAO1 strain, along with a decrease of up to 16-fold with either amikacin or colistin for clinical isolates. Taken together, these data characterize the new Pseudomonas phage Ka2 as a promising tool for the combined treatment of infections associated with P. aeruginosa biofilms.

MAGqual: a stand-alone pipeline to assess the quality of metagenome-assembled genomes

BACKGROUND

Metagenomics, the whole genome sequencing of microbial communities, has provided insight into complex ecosystems. It has facilitated the discovery of novel microorganisms, explained community interactions and found applications in various fields. Advances in high-throughput and third-generation sequencing technologies have further fuelled its popularity. Nevertheless, managing the vast data produced and addressing variable dataset quality remain ongoing challenges. Another challenge arises from the number of assembly and binning strategies used across studies. Comparing datasets and analysis tools is complex as it requires the quantitative assessment of metagenome quality. The inherent limitations of metagenomic sequencing, which often involves sequencing complex communities, mean community members are challenging to interrogate with traditional culturing methods leading to many lacking reference sequences. MIMAG standards aim to provide a method to assess metagenome quality for comparison but have not been widely adopted.

RESULTS

To address the need for simple and quick metagenome quality assignation, here we introduce the pipeline MAGqual (Metagenome-Assembled Genome qualifier) and demonstrate its effectiveness at determining metagenomic dataset quality in the context of the MIMAG standards.

CONCLUSIONS

The MAGqual pipeline offers an accessible way to evaluate metagenome quality and generate metadata on a large scale. MAGqual is built in Snakemake to ensure readability and scalability, and its open-source nature promotes accessibility, community development, and ease of updates. MAGqual is built in Snakemake, R, and Python and is available under the MIT license on GitHub at https://github.com/ac1513/MAGqual . Video Abstract.

Biodiversity of microorganisms in the Baltic Sea: the power of novel methods in the identification of marine microbes

Until recently, the data on the diversity of the entire microbial community from the Baltic Sea were relatively rare and very scarce. However, modern molecular methods have provided new insights into this field with interesting results. They can be summarized as follows. (i) Although low salinity causes a reduction in the biodiversity of multicellular species relative to the populations of the North-East Atlantic, no such reduction occurs in bacterial diversity. (ii) Among cyanobacteria, the picocyanobacterial group dominates when considering gene abundance, while filamentous cyanobacteria dominate in means of biomass. (iii) The diversity of diatoms and dinoflagellates is significantly larger than described a few decades ago; however, molecular studies on these groups are still scarce. (iv) Knowledge gaps in other protistan communities are evident. (v) Salinity is the main limiting parameter of pelagic fungal community composition, while the benthic fungal diversity is shaped by water depth, salinity, and sediment C and N availability. (vi) Bacteriophages are the predominant group of viruses, while among viruses infecting eukaryotic hosts, Phycodnaviridae are the most abundant; the Baltic Sea virome is contaminated with viruses originating from urban and/or industrial habitats. These features make the Baltic Sea microbiome specific and unique among other marine environments.

DeGenPrime provides robust primer design and optimization unlocking the biosphere

Motivation

Polymerase chain reaction (PCR) is the world's most important molecular diagnostic with applications ranging from medicine to ecology. PCR can fail because of poor primer design. The nearest-neighbor thermodynamic properties, picking conserved regions, and filtration via penalty of oligonucleotides form the basis for good primer design.

Results

DeGenPrime is a console-based high-quality PCR primer design tool that can utilize MSA formats and degenerate bases expanding the target range for a single primer set. Our software utilizes thermodynamic properties, filtration metrics, penalty scoring, and conserved region finding of any proposed primer. It has degeneracy, repeated k-mers, relative GC content, and temperature range filters. Minimal penalty scoring is included according to secondary structure self-dimerization metrics, GC clamping, tri- and tetra-loop hairpins, and internal repetition. We compared PrimerDesign-M, DegePrime, ConsensusPrimer, and DeGenPrime on acceptable primer yield. PrimerDesign-M, DegePrime, and ConsensusPrimer provided 0%, 11%, and 17% yield, respectively, for the alternative iron nitrogenase (anfD) gene target. DeGenPrime successfully identified quality primers within the conserved regions of the T4-like phage major capsid protein (g23), conserved regions of molybdenum-based nitrogenase (nif), and its alternatives vanadium (vnf) and iron (anf) nitrogenase. DeGenPrime provides a universal and scalable primer design tool for the entire tree of life.

Availability and implementation

DeGenPrime is written in C++ and distributed under a BSD-3-Clause license. The source code for DeGenPrime is freely available on www.github.com/raw-lab/degenprime.

Evaluating endogenous viral targets as potential treatment monitoring surrogates for onsite non-potable water reuse

Onsite non-potable water reuse systems (ONWS) are decentralized systems that treat and repurpose locally collected waters (e.g. greywater or combined wastewater) for uses such as irrigation and flushing toilets. To ensure that treatment is meeting risk benchmarks, it is necessary to monitor the efficacy of pathogen removal. However, accurate assessment of pathogen reduction is hampered by their sporadic and low occurrence rates in source waters and concentrations in treated water that are generally below measurement detection limits. An alternative metric for evaluation of onsite water treatment is log reduction of a more abundant organism that can serve as a surrogate for the pathogen removal. Viruses endogenous to the decentralized system could serve as monitoring surrogates to verify that treatment meets the relevant viral log reduction targets. This study assesses eight candidate PCR targets representing potential monitoring surrogates from different viral classes to determine whether they could be used to verify the efficacy of treatment in onsite non-potable water reuse systems. Candidates tested include markers for Carjivirus (formerly CrAssphage), Pepper Mild Mottle Virus (PMMoV), Microviridae, and T4 Coliphage. We quantified these targets in untreated influent wastewater at three onsite non-potable water reuse systems, two that use greywater and one that uses combined wastewater. We also confirmed, using amplicon sequencing, that the widely used Carjivirus and PMMoV primers correctly target their respective regions of interest, and found sequence diversity within the amplicons including in the probe binding region. Ultimately, we found that the surrogates assessed are not abundant enough for end uses with higher exposure use and concomitant greater removal requirements (e.g., indoor non-potable uses), but may be effective for end uses where exposure risk is lower (e.g., irrigation).

The structure and assembly mechanisms of T4-like cyanophages community in the South China Sea

Marine ecosystems contain an immense diversity of phages, many of which infect cyanobacteria (cyanophage) that are largely responsible for primary productivity. To characterize the genetic diversity and biogeographic distribution of the marine T4-like cyanophage community in the northern South China Sea, the T4-like cyanophage portal protein gene (g20) was amplified. Phylogenetic analysis revealed that marine T4-like cyanophages were highly diverse, with g20 operational taxonomic units being affiliated with five defined clades (Clusters I-V). Cluster II had a wide geographic distribution, Cluster IV was the most abundant in the open sea, and Cluster I was dominant in coastal shelf environments. Our results showed T4-like cyanophages (based on g20) community was generally shaped via heterogeneous selection. Highly variable environmental factors (such as salinity and temperature) can heterogeneously select different cyanophage communities. Nevertheless, the dominant drivers of the T4-like cyanophage community based on the g20 and g23 (T4-like phage major capsid protein gene) were different, probably due to different coverages by the primer sets. Furthermore, the community assembly processes of T4-like cyanophages were affected by host traits (abundance and distribution), viral traits (latent period, burst size, and host range), and environmental properties (temperature and salinity).IMPORTANCECyanophages are abundant and ubiquitous in the oceans, altering population structures and evolution of cyanobacteria, which account for a large portion of global carbon fixation, through host mortality, horizontal gene transfer, and the modulation of host metabolism. However, little is known about the biogeography and ecological drivers that shape the cyanophage community. Here, we use g20 and g23 genes to examine the biogeographic patterns and the assembly mechanisms of T4-like cyanophage community in the northern part of the South China Sea. The different coverages of primer sets might lead to the different dominant drivers of T4-like cyanophage community based on g20 and g23 genes. Our results showed that characteristics of viral traits (latent period, burst size, and host range) and host traits (abundance and distribution) were found to either limit or enhance the biogeographic distribution of T4-like cyanophages. Overall, both virus and host properties are critical to consider when determining rules of community assembly for viruses.

Temperature-dependent trophic associations modulate soil bacterial communities along latitudinal gradients

Understanding the environmental and biological mechanisms shaping latitudinal patterns in microbial diversity is challenging in the field of ecology. Although multiple hypotheses have been proposed to explain these patterns, a consensus has rarely been reached. Here, we conducted a large-scale field survey and microcosm experiments to investigate how environmental heterogeneity and putative trophic interactions (exerted by protist-bacteria associations and T4-like virus-bacteria associations) affect soil bacterial communities along a latitudinal gradient. We found that the microbial latitudinal diversity was kingdom dependent, showing decreasing, clumped, and increasing trends in bacteria, protists, and T4-like viruses, respectively. Climatic and edaphic drivers played predominant roles in structuring the bacterial communities; the intensity of the climatic effect increased sharply from 30°N to 32°N, whereas the intensity of the edaphic effect remained stable. Biotic associations were also essential in shaping the bacterial communities, with protist-bacteria associations showing a quadratic distribution, whereas virus-bacteria associations were significant only at high latitudes. The microcosm experiments further revealed that the temperature component, which is affiliated with climate conditions, is the primary regulator of trophic associations along the latitudinal gradient. Overall, our study highlights a previously underestimated mechanism of how the putative biotic interactions influence bacterial communities and their response to environmental gradients.

Spatiotemporal Shift of T4-Like Phage Community Structure in the Three Largest Estuaries of China

Estuaries are one of the most highly productive and economically important ecosystems at the continent-ocean interface. Estuary productivity is largely determined by the microbial community structure and activity. Viruses are major agents of microbial mortality and are key drivers of global geochemical cycles. However, the taxonomic diversity of viral communities and their spatial-temporal distribution in estuarine ecosystems have been poorly studied. In this study, we investigated the T4-like viral community composition at three major Chinese estuaries in winter and in summer. Diverse T4-like viruses, which were divided into three main clusters (Clusters I to III), were revealed. The Marine Group of Cluster III, with seven identified subgroups, was the most dominant (averaging 76.5% of the total sequences) in the Chinese estuarine ecosystems. Significant variations of T4-like viral community composition were observed among estuaries and seasons, with higher diversity occurring in winter. Among various environmental variables, temperature was a main driver of the viral communities. This study demonstrates viral assemblage diversification and seasonality in Chinese estuarine ecosystems. IMPORTANCE Viruses are ubiquitous but largely uncharacterized members of aquatic environments that cause significant mortality in microbial communities. Recent large-scale oceanic projects have greatly advanced our understanding of viral ecology in marine environments, but those studies mostly focused on oceanic regions. There have yet to be spatiotemporal studies of viral communities in estuarine ecosystems, which are unique habitats that play a significant role in global ecology and biogeochemistry. This work is the first comprehensive study that provides a detailed picture of the spatial and seasonal variation of viral communities (specifically, T4-like viral communities) in three major estuarine ecosystems in China. These findings provide much-needed knowledge regarding estuarine viral ecosystems, which currently lags in oceanic ecosystem research.

Effects of phytoplankton, viral communities, and warming on free-living and particle-associated marine prokaryotic community structure

Free-living and particle-associated marine prokaryotes have physiological, genomic, and phylogenetic differences, yet factors influencing their temporal dynamics remain poorly constrained. In this study, we quantify the entire microbial community composition monthly over several years, including viruses, prokaryotes, phytoplankton, and total protists, from the San-Pedro Ocean Time-series using ribosomal RNA sequencing and viral metagenomics. Canonical analyses show that in addition to physicochemical factors, the double-stranded DNA viral community is the strongest factor predicting free-living prokaryotes, explaining 28% of variability, whereas the phytoplankton (via chloroplast 16S rRNA) community is strongest with particle-associated prokaryotes, explaining 31% of variability. Unexpectedly, protist community explains little variability. Our findings suggest that biotic interactions are significant determinants of the temporal dynamics of prokaryotes, and the relative importance of specific interactions varies depending on lifestyles. Also, warming influenced the prokaryotic community, which largely remained oligotrophic summer-like throughout 2014-15, with cyanobacterial populations shifting from cold-water ecotypes to warm-water ecotypes.

Isolation and characterization of bacteriophage Ib_pec2 against shigatoxigenic Escherichia coli

This study was aimed to isolate and characterize bacteriophage against drug-resistant, shigatoxigenic Escherichia coli (STEC), one of the zoonotic, food-borne organisms associated with ruminants, mainly cattle. STEC were isolated (n = 35) from neonatal calves, dairy workers, and the surrounding environment and their antimicrobial resistance pattern was studied. Out of the 35 isolates tested, 17 isolates were found to be multidrug resistant to important antibiotics like ampicillin, amoxicillin-clavulanate, ciprofloxacin, streptomycin, and tetracycline. Bacteriophage namely Ib_pec2 was isolated against one of the STEC isolates and its morphology, genetic and proteomic characterization was done. Morphological analysis by TEM revealed bacteriophages belonging to myoviridae family. The genetic characterization of g23 gene revealed that the bacteriophage belonged to Tequatrovirus of myoviridae family. Proteomic analysis was able to identify five proteins identical to Tequatrovirus of myoviridae family. One-step growth curve experiment revealed a latency period of 40 min and a burst size of 893 pfu/bacteria. Temperature and pH ranging from 40°C to 50°C, pH 6-8, respectively. Phage could able to lyse majority of the STEC isolates. STEC are commensal organisms in the gastrointestinal tract of ruminants but are pathogenic in humans. Bacteriophages can be used as alternatives to antibiotics to control bacterial growth in ruminants and prevent its further spillage in the environment.

Improving high-throughput techniques for bacteriophage discovery in multi-well plates

Bacteriophages (also called phages) are viruses of bacteria that have numerous applications in medicine, agriculture, ecology, and molecular biology. With the increasing interest in phages for their many uses, it is now especially important to make phage discovery more efficient and economical. Using the host Mycobacterium smegmatis mc²155, which is a model organism for phage discovery research and is closely related to important pathogens of humans and other animals, we investigated three procedures that are an integral part of phage discovery: enrichment of environmental samples, phage isolation and detection (which can also be used for host range determination), and phage purification. Enrichment in 6-well plates was successful with most environmental samples, and enrichment in 24- and 96-well plates was successful with some environmental samples, demonstrating that larger sample volumes are preferred when possible, but smaller sample volumes may be acceptable if the starting concentration of phages is sufficiently high. Measuring absorbance in multi-well plates was at least as sensitive as the traditional plaque assay for the detection of phages. We also demonstrated a technique for the purification of single phage types from mixed cultures in liquid medium. Multi-well techniques can be used as alternatives or complementary approaches to traditional methods of phage discovery and characterization depending on the needs of the researcher in terms of time, available resources, host species, phage-bacteria matches, and specific goals. In the future, these techniques could be applied to the discovery of phages of aquatic mycobacteria and other hosts for which few phages have currently been isolated.

Microbial communities of halite deposits and other hypersaline environments

Large regions of Earth's surface are underlain by salt deposits that evaporated from ancient oceans and are populated by extreme halophilic microbes. While the microbiology of ancient evaporites has been well studied, the ecology of halite deposits and more recently formed NaCl "salticle" stalactite structures (speleothems) in a Triassic halite mine are less well characterized. The microbiome of Kilroot Salt Mine was profiled using conventional and enhanced culturing techniques. From this, 89 halophilic archaeal isolates from six known genera, and 55 halophilic or halotolerant bacterial isolates from 18 genera were obtained. Culture-independent metagenomic approaches also revealed that culturing techniques were inadvertently biased toward specific taxa, and the need for optimized isolation procedures are required to enhance cultivation diversity. Speleothems formed from saturated brines are unique structures that have the potential to entomb haloarchaea cells for thousands of years within fluid inclusions. The presence of such fluid inclusions, alongside the high abundance of genes related to glycerol metabolism, biofilm formation, and persister cell formation is highly suggestive of an environmental niche that could promote longevity and survivability. Finally, previous studies reporting the discovery of novel biocatalysts from the Kilroot mine microbiome, suggests that this environment may be an untapped source of chemical diversity with high biodiscovery potential.

The Beauty of Bacteriophage T4 Research: Lindsay W. Black and the T4 Head Assembly

Viruses are biochemically complex structures and mainly consist of folded proteins that contain nucleic acids. Bacteriophage T4 is one of most prominent examples, having a tail structure that contracts during the infection process. Intracellular phage multiplication leads to separate self-directed assembly reactions of proheads, tails and tail fibers. The proheads are packaged with concatemeric DNA produced by tandem replication reactions of the parental DNA molecule. Once DNA packaging is completed, the head is joined with the tail and six long fibers are attached. The mature particles are then released from the cell via lysis, another tightly regulated process. These processes have been studied in molecular detail leading to a fascinating view of the protein-folding dynamics that direct the structural interplay of assembled complexes. Lindsay W. Black dedicated his career to identifying and defining the molecular events required to form the T4 virion. He leaves us with rich insights into the astonishingly precise molecular clockwork that co-ordinates all of the players in T4 assembly, both viral and cellular. Here, we summarize Lindsay’s key research contributions that are certain to stimulate our future science for many years to come.

Unravelling the ecological complexity of soil viromes: Challenges and opportunities

Viruses are extremely abundant and ubiquitous in soil, and significantly contribute to various terrestrial ecosystem processes such as biogeochemical nutrient cycling, microbiome regulation and community assembly, and host evolutionary dynamics. Despite their numerous dominance and functional importance, understanding soil viral ecology is a formidable challenge, because of the technological challenges to characterize the abundance, diversity and community compositions of viruses, and their interactions with other organisms in the complex soil environment. Viruses may engage in a myriad of biological interactions within soil food webs across a broad range of spatiotemporal scales and are exposed to various biotic and abiotic disturbances. Current studies on the soil viromes, however, often describe the complexity of their tremendous diversity, but lack of exploring their potential ecological roles. In this article, we summarized the major methods to decipher the ecology of soil viruses, discussed biotic and abiotic factors and global change factors that shape the diversity and composition of soil viromes, and the ecological roles of soil viruses. We also proposed a new framework to understand the ecological complexity of viruses from micro to macro ecosystem scales and to predict and unravel their activities in terrestrial ecosystems.

Communities of T4-like bacteriophages associated with bacteria in Lake Baikal: diversity and biogeography

Lake Baikal phage communities are important for lake ecosystem functioning. Here we describe the diversity of T4-bacteriophage associated with the bacterial fraction of filtered water samples collected from the pelagic zone, coastal zone and shallow bays. Although the study of the diversity of phages for the g23 gene has been carried out at Lake Baikal for more than ten years, shallow bays that comprise a significant part of the lake’s area have been neglected, and this gene has not previously been studied in the bacterial fraction. Phage communities were probed using amplicon sequencing methods targeting the gene of major capsid protein (g23) and compared phylogenetically across sample locations and with sequences previously retrieved from non-bacterial fractions (<0.2 um) and biofilms (non-fractionated). In this study, we examined six water samples, in which 24 to 74 viral OTUs were obtained. The sequences from shallow bays largely differed from those in the pelagic and coastal samples and formed individual subcluster in the UPGMA tree that was obtained from the comparison of phylogenetic distances of g23 sequence sets from various ecosystems, reflecting differences in viral communities depending on the productivity of various sites of Lake Baikal. According to the RefSeq database, from 58.3 to 73% of sequences of each sample had cultivated closest relatives belonging to cyanophages. In this study, for phylogenetic analysis, we chose the closest relatives not only from the RefSeq and GenBank NR databases but also from two marine and one freshwater viromes: eutrophic Osaka Bay (Japan), oligotrophic area of the Pacific Ocean (Station ALOHA) and mesotrophic and ancient Lake Biwa (Japan), which allowed us to more fully compare the diversity of marine and freshwater phages. The identity with marine sequences at the amino acid level ranged from 35 to 80%, and with the sequences from the viral fraction and bacterial one from Lake Biwa—from 35.3 to 98% and from 33.9 to 89.1%, respectively. Therefore, the sequences from marine viromes had a greater difference than those from freshwater viromes, which may indicate a close relationship between freshwater viruses and differences from marine viruses.

Unique T4-like phages in high-altitude lakes above 4500 m on the Tibetan Plateau

Viruses are the most abundant biological entities in the biosphere; however, little is known about viral ecology in high altitude lakes. Here, we characterized viruses from 13 lakes, nine of which located ≥4500 m above sea level, on the Tibetan Plateau, the highest plateau on Earth. The abundance of virus-like particle (VLP) in Tibetan lakes ranged from 4.8 ± 0.2 × 10⁵ VLPs mL^-1 to 6.0 ± 0.2 × 10⁷ VLPs mL^-1 and the virus-to-bacterium ratio was in the lower range of values reported for other lakes. The viral population size was positively correlated with turbidity and negatively correlated with particulate organic carbon concentration. Highly diverse VLP morphologies, including large (~300 nm) morphotypes, were observed. Phylogenetic analysis of T4-like bacteriophages based on major capsid gene (g23) identified a novel viral group, which were detected in abundance in hyposaline and mesosaline Tibetan lakes. Adaptation to lake evolution, water source (glacier-fed or non-glacier-fed) and environmental conditions (e.g., salinity, phosphorus concentration and productivity) are likely responsible for the variation in T4-like myovirus community composition in contrasting Tibetan lakes. This first investigation of viruses in high-altitude alpine lakes above 4500 m could contribute to our understanding of viral ecology in global alpine lakes.

Going to extremes - a metagenomic journey into the dark matter of life

The Virus-X-Viral Metagenomics for Innovation Value-project was a scientific expedition to explore and exploit uncharted territory of genetic diversity in extreme natural environments such as geothermal hot springs and deep-sea ocean ecosystems. Specifically, the project was set to analyse and exploit viral metagenomes with the ultimate goal of developing new gene products with high innovation value for applications in biotechnology, pharmaceutical, medical, and the life science sectors. Viral gene pool analysis is also essential to obtain fundamental insight into ecosystem dynamics and to investigate how viruses influence the evolution of microbes and multicellular organisms. The Virus-X Consortium, established in 2016, included experts from eight European countries. The unique approach based on high throughput bioinformatics technologies combined with structural and functional studies resulted in the development of a biodiscovery pipeline of significant capacity and scale. The activities within the Virus-X consortium cover the entire range from bioprospecting and methods development in bioinformatics to protein production and characterisation, with the final goal of translating our results into new products for the bioeconomy. The significant impact the consortium made in all of these areas was possible due to the successful cooperation between expert teams that worked together to solve a complex scientific problem using state-of-the-art technologies as well as developing novel tools to explore the virosphere, widely considered as the last great frontier of life.

Characterization and in vitro activity of a lytic phage RDN37 isolated from community sewage water active against MDR Uropathogenic E. coli

PURPOSE

Due to the emergence of multidrug-resistant Uropathogenic E. coli (MDR-UPEC) strains, alternatives to antibiotics like phage therapy have been sought. The present study was planned to characterize and test the activity of a phage (RDN37) which was isolated from community sewage water of Chandigarh and was found to be active against MDR-UPEC.

MATERIALS AND METHODS

We studied the morphology of the phage by transmission electron microscopy and determined one-step growth curve analysis and stability of the phage at various temperature and pH ranges. PCR amplification and Sanger sequencing were performed to confirm the phage family. Genome sequences from 12 related phages (BLASTn identity >95%) were obtained from the NCBI database in GenBank format. A phylogenetic analysis was conducted using the neighbour-joining method in ClustalX2 and MEGAX. Host range and lytic activity were tested by spot assay and time-kill experiment, respectively.

RESULTS

Phage RDN37 had a large burst size and belonged to the Myoviridae family as per transmission electron microscopy and Sanger sequencing results. It was stable over wide range of temperature (-20°,4°, 25°, 37 °C) and pH (6,7,8). The phylogenetic analysis of amplified PCR product (major coat protein gp23) grouped the phage RDN37 with Escherichia phage vB_EcoM_IME537 (MT179807) isolated from community sewage water in China. RDN37 phage was active against MDR-UPEC strains resistant to third generation cephalosporins, aminoglycosides, carbapenems, fluoroquinolones and cotrimoxazole. The multiplicity of infection (MOI) of 0.01 was found to be optimum to reduce the bacterial cell density in the time-kill assay.

CONCLUSIONS

RDN37 is a stable lytic phage with large burst size, specific to E. coli, has a therapeutic potential to treat UTI caused by highly drug resistant UPEC. A cocktail of multiple phages will be required to overcome its narrow host range.

Role of Phylogenetic Structure in the Dynamics of Coastal Viral Assemblages

Marine microbes, including viruses, are an essential part of the marine ecosystem, forming the base of the food web and driving biogeochemical cycles. Within this system, the composition of viral assemblages changes markedly with time, and some of these changes are repeatable through time; however, the extent to which these dynamics are reflected within versus among evolutionarily related groups of viruses is largely unexplored. To examine these dynamics, changes in the composition of two groups of ecologically important viruses and communities of their potential hosts were sampled every 2 weeks for 13 months at a coastal site in British Columbia, Canada. We sequenced two marker genes for viruses-the gene encoding the major capsid protein of T4-like phages and their relatives (gp23) and the RNA-dependent RNA polymerase (RdRp) gene of marnavirus-like RNA viruses-as well as marker genes for their bacterial and eukaryotic host communities, the genes encoding 16S rRNA and 18S rRNA. There were strong lagged correlations between viral diversity and community similarity of putative hosts, implying that the viruses influenced the composition of the host communities. The results showed that for both viral assemblages, the dominant clusters of phylogenetically related viruses shifted over time, and this was correlated with environmental changes. Viral clusters contained many ephemeral taxa and few persistent taxa, but within a viral assemblage, the ephemeral and persistent taxa were closely related, implying ecological dynamics within these clusters. Furthermore, these dynamics occurred in both the RNA and DNA viral assemblages surveyed, implying that this structure is common in natural viral assemblages.IMPORTANCE Viruses are major agents of microbial mortality in marine systems, yet little is known about changes in the composition of viral assemblages in relation to those of the microbial communities that they infect. Here, we sampled coastal seawater every 2 weeks for 1 year and used high-throughput sequencing of marker genes to follow changes in the composition of two groups of ecologically important viruses, as well as the communities of bacteria and protists that serve as their respective hosts. Different subsets of genetically related viruses dominated at different times. These results demonstrate that although the genetic composition of viral assemblages is highly dynamic temporally, for the most part the shuffling of genotypes occurs within a few clusters of phylogenetically related viruses. Thus, it appears that even in temperate coastal waters with large seasonal changes, the highly dynamic shuffling of viral genotypes occurs largely within a few subsets of related individuals.

T4-like Phages Reveal the Potential Role of Viruses in Soil Organic Matter Mineralization

Viruses are the most abundant biological entities in the world, but their ecological functions in soil are virtually unknown. We hypothesized that greater abundance of T4-like phages will increase bacterial death and thereby suppress soil organic carbon (SOC) mineralization. A range of phage and bacterial abundances were established in sterilized soil by reinoculation with 10^-3 and 10^-6 dilutions of suspensions of unsterilized soil. The total and viable 16S rRNA gene abundance (a universal marker for bacteria) was measured by qPCR to determine bacterial abundance, with propidium monoazide (PMA) preapplication to eliminate DNA from non-viable cells. Abundance of the g23 marker gene was used to quantify T4-like phages. A close negative correlation between g23 abundance and viable 16S rRNA gene abundance was observed. High abundance of g23 led to lower viable ratios for bacteria, which suggested that phages drove microbial necromass production. The CO₂ efflux from soil increased with bacterial abundance but decreased with higher abundance of T4-like phages. Elimination of extracellular DNA by PMA strengthened the relationship between CO₂ efflux and bacterial abundance, suggesting that SOC mineralization by bacteria is strongly reduced by the T4-like phages. A random forest model revealed that abundance of T4-like phages and the abundance ratio of T4-like phages to bacteria are better predictors of SOC mineralization (measured as CO₂ efflux) than bacterial abundance. Our study provides experimental evidence of phages' role in organic matter turnover in soil: they can retard SOC decomposition but accelerate bacterial turnover.

Influence of Non-canonical DNA Bases on the Genomic Diversity of Tevenvirinae

The Tevenvirinae viruses are some of the most common viruses on Earth. Representatives of this subfamily have long been used in the molecular biology studies as model organisms – since the emergence of the discipline. Tevenvirinae are promising agents for phage therapy in animals and humans, since their representatives have only lytic life cycle and many of their host bacteria are pathogens. As confirmed experimentally, some Tevenvirinae have non-canonical DNA bases. Non-canonical bases can play an essential role in the diversification of closely related viruses. The article performs a comparative and evolutionary analysis of Tevenvirinae genomes and components of Tevenvirinae genomes. A comparative analysis of these genomes and the genes associated with the synthesis of non-canonical bases allows us to conclude that non-canonical bases have a major influence on the divergence of Tevenvirinae viruses within the same habitats. Supposedly, Tevenvirinae developed a strategy for changing HGT frequency in individual populations, which was based on the accumulation of proteins for the synthesis of non-canonical bases and proteins that used those bases as substrates. Owing to this strategy, ancestors of Tevenvirinae with the highest frequency of HGT acquired genes that allowed them to exist in a certain niche, and ancestors with the lowest HGT frequency preserved the most adaptive of those genes. Given the origin and characteristics of genes associated with the synthesis of non-canonical bases in Tevenvirinae, one can assume that other phages may have similar strategies. The article demonstrates the dependence of genomic diversity of closely related Tevenvirinae on non-canonical bases.

Complete genome analysis of an active prophage of Vibrio alginolyticus

An active prophage, Vibrio phage ValM-yong1, was isolated from pathogenic Vibrio alginolyticus by mitomycin C induction. This phage is a member of the family Myoviridae and contains a head approximately 90 nm in diameter and a retractable tail approximately 250 nm in length. The genome of the phage is 33,851 bp in length with a G+C content of 45.6%. The noteworthy features of Vibrio phage ValM-yong1 are its flower-like head and genomic mosaicism. Here, we focus on presenting the genomic characterization of the virus.

T4-like myovirus community shaped by dispersal and deterministic processes in the South China Sea

As the most abundant and genetically diverse biological entities, viruses significantly influence ecological, biogeographical and evolutionary processes in the ocean. However, the biogeography of marine viruses and the drivers shaping viral community are unclear. Here, the biogeographic patterns of T4-like viruses and the relative impacts of deterministic (environmental selection) and dispersal (spatial distance) processes were investigated in the northern South China Sea. The dominant viral operational taxonomic units were affiliated with previously defined Marine, Estuary, Lake and Paddy Groups. A clear viral biogeographic pattern was observed along the environmental gradient from the estuary to open sea. Marine Groups I and IV had a wide geographical distribution, whereas Marine Groups II, III and V were abundant in lower-salinity continental or eutrophic environments. A significant distance-decay pattern was noted for the T4-like viral community, especially for those infecting cyanobacteria. Both deterministic and dispersal processes influenced viral community assembly, although environmental selection (e.g. temperature, salinity, bacterial abundance and community, etc.) had a greater impact than spatial distance. Network analysis confirmed the strong association between viral and bacterial community composition, and suggested a diverse ecological relationship (e.g. lysis, co-infection or mutualistic) between and within viruses and their potential bacterial hosts.

Metagenome Mining Reveals Hidden Genomic Diversity of Pelagimyophages in Aquatic Environments

SAR11 clade members are among the most abundant bacteria on Earth. Their study is complicated by their great diversity and difficulties in being grown and manipulated in the laboratory. On the other hand, and due to their extraordinary abundance, metagenomic data sets provide enormous richness of information about these microbes. Given the major role played by phages in the lifestyle and evolution of prokaryotic cells, the contribution of several new bacteriophage genomes preying on this clade opens windows into the infection strategies and life cycle of its viruses. Such strategies could provide models of attack of large-genome phages preying on streamlined aquatic microbes.

The SAR11 clade is one of the most abundant bacterioplankton groups in surface waters of most of the oceans and lakes. However, only 15 SAR11 phages have been isolated thus far, and only one of them belongs to the Myoviridae family (pelagimyophages). Here, we have analyzed 26 sequences of myophages that putatively infect the SAR11 clade. They have been retrieved by mining ca. 45 Gbp aquatic assembled cellular metagenomes and viromes. Most of the myophages were obtained from the cellular fraction (0.2 μm), indicating a bias against this type of virus in viromes. We have found the first myophages that putatively infect Candidatus Fonsibacter (freshwater SAR11) and another group putatively infecting bathypelagic SAR11 phylogroup Ic. The genomes have similar sizes and maintain overall synteny in spite of low average nucleotide identity values, revealing high similarity to marine cyanomyophages. Pelagimyophages recruited metagenomic reads widely from several locations but always much more from cellular metagenomes than from viromes, opposite to what happens with pelagipodophages. Comparing the genomes resulted in the identification of a hypervariable island that is related to host recognition. Interestingly, some genes in these islands could be related to host cell wall synthesis and coinfection avoidance. A cluster of curli-related proteins was widespread among the genomes, although its function is unclear.

IMPORTANCE SAR11 clade members are among the most abundant bacteria on Earth. Their study is complicated by their great diversity and difficulties in being grown and manipulated in the laboratory. On the other hand, and due to their extraordinary abundance, metagenomic data sets provide enormous richness of information about these microbes. Given the major role played by phages in the lifestyle and evolution of prokaryotic cells, the contribution of several new bacteriophage genomes preying on this clade opens windows into the infection strategies and life cycle of its viruses. Such strategies could provide models of attack of large-genome phages preying on streamlined aquatic microbes.

Widespread cryptic viral infections in lotic biofilms

Viruses have important impacts on aquatic microbial ecology and have been studied at length in the global ocean. However, the roles of bacteriophages in lotic ecosystems, particularly in benthic biofilms, have been largely under-studied. The main goals of this work were to determine whether viruses are consistent members of natural benthic biofilm communities of freshwater streams; whether temperate phages are present and active in such biofilms; and whether community profiling approaches like RAPD-PCR can be adapted to characterize biofilm virus communities. Results from both field and laboratory experiments suggest that viruses are consistent members of lotic biofilm communities. Interestingly, prophage induction was statistically significant but only a small percentage of the total bacterial population appeared to harbor prophage or engaged in induction. Finally, while the use of RAPD-PCR for the community level profiling of biofilm viral communities suggests temporal change in response to biofilm maturity, further refinements are required for broad-scale quantitative application.

Isolation and Genome Sequencing of a Novel Pseudomonas aeruginosa Phage PA-YS35

Phage PA-YS35 is a novel lytic Pseudomonas aeruginosa phage belonging to the Myoviridae family and was isolated from the sewage of the First Hospital of Jilin University. The biological properties testing indicated that phage PA-YS35 is stable between - 20 and 60 °C and pH 4-9. The one-step growth curve shows that the latent period of PA-YS35 was 9 min, and the burst period was about 21 min by the size of approximately 380 progeny phages per host cell. The genome of phage PA-YS35 is linear double-stranded DNA with a size of 93,296 bp and a GC content of 49.35%. The results from RAST gene annotation analysis showed that the PA-YS35 genome contains 172 open reading frames (ORFs); the function of 41 ORFs can be predicted, whereas the product of remaining 131 ORFs are hypothetical proteins. According to phylogenetic tree of RNA ligase encoding sequence, phage PA-YS35 has a close evolutionary relationship with Pseudomonas phage PAK P1 because both of them are located on the same branch. The study of phage PA-YS35 genome will provide useful information for further research on the interaction between phages and their hosts.

Metagenomic Analysis of Virioplankton from the Pelagic Zone of Lake Baikal

This study describes two viral communities from the world’s oldest lake, Lake Baikal. For the analysis, we chose under-ice and late spring periods of the year as the most productive for Lake Baikal. These periods show the maximum seasonal biomass of phytoplankton and bacterioplankton, which are targets for viruses, including bacteriophages. At that time, the main group of viruses were tailed bacteriophages of the order Caudovirales that belong to the families Myoviridae, Siphoviridae and Podoviridae. Annotation of functional genes revealed that during the under-ice period, the “Phages, Prophages, Transposable Elements and Plasmids” (27.4%) category represented the bulk of the virome. In the late spring period, it comprised 9.6% of the virome. We assembled contigs by two methods: Separately assembled in each virome or cross-assembled. A comparative analysis of the Baikal viromes with other aquatic environments indicated a distribution pattern by soil, marine and freshwater groups. Viromes of lakes Baikal, Michigan, Erie and Ontario form the joint World’s Largest Lakes clade.

Genomic analyses of two novel biofilm-degrading methicillin-resistant Staphylococcus aureus phages

Background

Methicillin-resistant Staphylococcus aureus (MRSA) biofilm producers represent an important etiological agent of many chronic human infections. Antibiotics and host immune responses are largely ineffective against bacteria within biofilms. Alternative actions and novel antimicrobials should be considered. In this context, the use of phages to destroy MRSA biofilms presents an innovative alternative mechanism.

Results

Twenty-five MRSA biofilm producers were used as substrates to isolate MRSA-specific phages. Despite the difficulties in obtaining an isolate of this phage, two phages (UPMK_1 and UPMK_2) were isolated. Both phages varied in their ability to produce halos around their plaques, host infectivity, one-step growth curves, and electron microscopy features. Furthermore, both phages demonstrated antagonistic infectivity on planktonic cultures. This was validated in an in vitro static biofilm assay (in microtiter-plates), followed by the visualization of the biofilm architecture in situ via confocal laser scanning microscopy before and after phage infection, and further supported by phages genome analysis. The UPMK_1 genome comprised 152,788 bp coding for 155 putative open reading frames (ORFs), and its genome characteristics were between the Myoviridae and Siphoviridae family, though the morphological features confined it more to the Siphoviridae family. The UPMK_2 has 40,955 bp with 62 putative ORFs; morphologically, it presented the features of the Podoviridae though its genome did not show similarity with any of the S. aureus in the Podoviridae family. Both phages possess lytic enzymes that were associated with a high ability to degrade biofilms as shown in the microtiter plate and CLSM analyses.

Conclusions

The present work addressed the possibility of using phages as potential biocontrol agents for biofilm-producing MRSA.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1484-9) contains supplementary material, which is available to authorized users.

The Environment and Cyanophage Diversity: Insights From Environmental Sequencing of DNA Polymerase

Globally distributed and abundant cyanophages in the family Myoviridae have dsDNA genomes with variable gene content, including host-derived auxiliary metabolic genes (AMGs) that potentially can facilitate viral replication. However, it is not well understood how this variation in gene content interacts with environmental variables to shape cyanomyovirus communities. This project correlated the genetic repertoire of cyanomyoviruses with their phyologeny, and investigated cyanomyovirus ecotype distribution as a function of environmental conditions across locations and seasons. Reference cyanomyovirus genomes were compared for their overlap in gene content to infer phyologenetic distances, and these distances were compared to distances calculated based on DNA polymerase (gp43) gene sequences. In turn, gp43 partial gene sequences amplified from natural cyanophage communities were used to describe cyanomyovirus community composition and to assess the relationship between environmental variables. The results showed the following: (1) DNA polymerase gene phylogeny generally correlated with the similarity in gene content among reference cyanomyoviruses, and thus can be used to describe environmental cyanomyovirus communities; (2) spatial and seasonal patterns in cyanomyovirus communities were related to environmental variables; (3) salinity and temperature, combined with nutrient concentration were predictors of cyanomyovirus richness, diversity and community composition. This study shows that environmental variables shape viral communities by drawing on a diverse seed bank of viral genotypes. From these results it is evident that that viral ecotypes with their corresponding genetic repertoires underlie selection pressures. However, the mechanisms involved in selecting for specific viral genotypes remain to be fully understood.

Survey of the bacteriophage phoH gene in wetland sediments in northeast China

PhoH is a host-derived auxiliary metabolic gene that can be used as a new biomarker for surveying phage diversity in marine and paddy waters. However, the applicability of this gene in other environments has not been addressed. In this paper, we surveyed the phoH gene in four wetland sediments in northeast China. DNA was extracted directly from sediments and used for PCR amplification with the degenerate primers vPhoHf and vPhoHr. In total, 44 and 58 phoH sequences were identified as belonging to bacteria and phages, respectively, suggesting that this primer set is not highly specific to the phage phoH gene. A BLASTp search showed that the 58 phage phoH sequences had the highest identity to the known viral sequences, ranging from 48% to 100%. Phylogenetic analysis showed that all phage sequences from wetlands distributed into the previously designated Groups 2, 3, 4 and 6. In addition, two new subgroups, Groups 2c and 4c, which contained sequences exclusively from wetlands, were detected in this study. Nonmetric multidimensional scaling analysis showed that the phage phoH assemblage from a coastal wetland was similar to that in marine environments, while the phage phoH assemblage from a lake wetland was similar to that in paddy waters. These findings indicated that different types of wetlands had distinct phage phoH compositions.

Seasonality Drives Microbial Community Structure, Shaping both Eukaryotic and Prokaryotic Host⁻Viral Relationships in an Arctic Marine Ecosystem

The Arctic marine environment experiences dramatic seasonal changes in light and nutrient availability. To investigate the influence of seasonality on Arctic marine virus communities, five research cruises to the west and north of Svalbard were conducted across one calendar year, collecting water from the surface to 1000 m in depth. We employed metabarcoding analysis of major capsid protein g23 and mcp genes in order to investigate T4-like myoviruses and large dsDNA viruses infecting prokaryotic and eukaryotic picophytoplankton, respectively. Microbial abundances were assessed using flow cytometry. Metabarcoding results demonstrated that seasonality was the key mediator shaping virus communities, whereas depth exerted a diversifying effect within seasonal virus assemblages. Viral diversity and virus-to-prokaryote ratios (VPRs) dropped sharply at the commencement of the spring bloom but increased across the season, ultimately achieving the highest levels during the winter season. These findings suggest that viral lysis may be an important process during the polar winter, when productivity is low. Furthermore, winter viral communities consisted of Operational Taxonomic Units (OTUs) distinct from those present during the spring-summer season. Our data provided a first insight into the diversity of viruses in a hitherto undescribed marine habitat characterized by extremes in light and productivity.

Novel T4 bacteriophages associated with black band disease in corals

Research into causative agents underlying coral disease have focused primarily on bacteria, whereas potential roles of viruses have been largely unaddressed. Bacteriophages may contribute to diseases through the lysogenic introduction of virulence genes into bacteria, or prevent diseases through lysis of bacterial pathogens. To identify candidate phages that may influence the pathogenicity of black band disease (BBD), communities of bacteria (16S rRNA) and T4-bacteriophages (gp23) were simultaneously profiled with amplicon sequencing among BBD-lesions and healthy-coral-tissue of Montipora hispida, as well as seawater (study site: the central Great Barrier Reef). Bacterial community compositions were distinct among BBD-lesions, healthy coral tissue and seawater samples, as observed in previous studies. Surprisingly, however, viral beta diversities based on both operational taxonomic unit (OTU)-compositions and overall viral community compositions of assigned taxa did not differ statistically between the BBD-lesions and healthy coral tissue. Nonetheless, relative abundances of three bacteriophage OTUs, affiliated to Cyanophage PRSM6 and Prochlorococcus phages P-SSM2, were significantly higher in BBD-lesions than in healthy tissue. These OTUs associated with BBD samples suggest the presence of bacteriophages that infect members of the cyanobacteria-dominated BBD community, and thus have potential roles in BBD pathogenicity.

In vitro reconstitution of DNA replication initiated by genetic recombination: a T4 bacteriophage model for a type of DNA synthesis important for all cells

Using a mixture of 10 purified DNA replication and DNA recombination proteins encoded by the bacteriophage T4 genome, plus two homologous DNA molecules, we have reconstituted the genetic recombination–initiated pathway that initiates DNA replication forks at late times of T4 bacteriophage infection. Inside the cell, this recombination-dependent replication (RDR) is needed to produce the long concatemeric T4 DNA molecules that serve as substrates for packaging the shorter, genome-sized viral DNA into phage heads. The five T4 proteins that catalyze DNA synthesis on the leading strand, plus the proteins required for lagging-strand DNA synthesis, are essential for the reaction, as are a special mediator protein (gp59) and a Rad51/RecA analogue (the T4 UvsX strand-exchange protein). Related forms of RDR are widespread in living organisms—for example, they play critical roles in the homologous recombination events that can restore broken ends of the DNA double helix, restart broken DNA replication forks, and cross over chromatids during meiosis in eukaryotes. Those processes are considerably more complex, and the results presented here should be informative for dissecting their detailed mechanisms.

Characterization and Genomic Analyses of Pseudomonas aeruginosa Podovirus TC6: Establishment of Genus Pa11virus

Phages have attracted a renewed interest as alternative to chemical antibiotics. Although the number of phages is 10-fold higher than that of bacteria, the number of genomically characterized phages is far less than that of bacteria. In this study, phage TC6, a novel lytic virus of Pseudomonas aeruginosa, was isolated and characterized. TC6 consists of an icosahedral head with a diameter of approximately 54 nm and a short tail with a length of about 17 nm, which are characteristics of the family Podoviridae. TC6 can lyse 86 out of 233 clinically isolated P. aeruginosa strains, thus showing application potentials for phage therapy. The linear double-stranded genomic DNA of TC6 consisted of 49796 base pairs and was predicted to contain 71 protein-coding genes. A total of 11 TC6 structural proteins were identified by mass spectrometry. Comparative analysis revealed that the P. aeruginosa phages TC6, O4, PA11, and IME180 shared high similarity at DNA sequence and proteome levels, among which PA11 was the first phage discovered and published. Meanwhile, these phages contain 54 core genes and have very close phylogenetic relationships, which distinguish them from other known phage genera. We therefore proposed that these four phages can be classified as Pa11virus, comprising a new phage genus of Podoviridae that infects Pseudomonas spp. The results of this work promoted our understanding of phage biology, classification, and diversity.

MARVEL, a Tool for Prediction of Bacteriophage Sequences in Metagenomic Bins

Here we present MARVEL, a tool for prediction of double-stranded DNA bacteriophage sequences in metagenomic bins. MARVEL uses a random forest machine learning approach. We trained the program on a dataset with 1,247 phage and 1,029 bacterial genomes, and tested it on a dataset with 335 bacterial and 177 phage genomes. We show that three simple genomic features extracted from contig sequences were sufficient to achieve a good performance in separating bacterial from phage sequences: gene density, strand shifts, and fraction of significant hits to a viral protein database. We compared the performance of MARVEL to that of VirSorter and VirFinder, two popular programs for predicting viral sequences. Our results show that all three programs have comparable specificity, but MARVEL achieves much better performance on the recall (sensitivity) measure. This means that MARVEL should be able to identify many more phage sequences in metagenomic bins than heretofore has been possible. In a simple test with real data, containing mostly bacterial sequences, MARVEL classified 58 out of 209 bins as phage genomes; other evidence suggests that 57 of these 58 bins are novel phage sequences. MARVEL is freely available at https://github.com/LaboratorioBioinformatica/MARVEL.

Water Masses and Depth Structure Prokaryotic and T4-Like Viral Communities Around Hydrothermal Systems of the Nordic Seas

The oceanographic features of the Nordic Seas, situated between Iceland and Svalbard, have been extensively studied over the last decades. As well, the Nordic Seas hydrothermal systems situated on the Arctic Mid-Ocean Ridge System have received an increasing interest. However, there is very little knowledge on the microbial communities inhabiting the water column of the Nordic Seas, and nothing is known about the influence of the different water masses and hydrothermal plumes on the microbial community structures. In this study, we aimed at characterizing the impact of hydrothermal plumes on prokaryotic and T4-like viral communities around the island of Jan Mayen. To this end, we used 16S rRNA-gene and g23-gene profiling as well as flow cytometry counts to examine prokaryotic and viral communities in 27 samples obtained from different water masses in this area. While Thaumarchaeota and Marine group II Archaea dominated the waters deeper than 500 m, members of Flavobacteria generally dominated the shallower waters. Furthermore, extensive chemical and physical characteristics of all samples were obtained, including temperature measurements and concentrations of major ions and gases. The effect of these physiochemical variables on the communities was measured by using constrained and unconstrained multivariate analyzes, Mantel tests, network analyzes, phylogenetic analyzes, taxonomic analyzes and temperature-salinity (Θ-S) plots. Our results suggest that hydrothermal activity has little effect on pelagic microbial communities in hydrothermal plumes of the Nordic Seas. However, we provide evidences that observed differences in prokaryotic community structure can largely be attributed to which water mass each sample was taken from. In contrast, depth was the major factor structuring the T4-like viral communities. Our results also show that it is crucial to include water masses when studying the influence of hydrothermal plumes on microbial communities, as it could prevent to falsely associate a change in community structure with the presence of a plume.

High Diversity of Myocyanophage in Various Aquatic Environments Revealed by High-Throughput Sequencing of Major Capsid Protein Gene With a New Set of Primers

Myocyanophages, a group of viruses infecting cyanobacteria, are abundant and play important roles in elemental cycling. Here we investigated the particle-associated viral communities retained on 0.2 μm filters and in sediment samples (representing ancient cyanophage communities) from four ocean and three lake locations, using high-throughput sequencing and a newly designed primer pair targeting a gene fragment (∼145-bp in length) encoding the cyanophage gp23 major capsid protein (MCP). Diverse viral communities were detected in all samples. The fragments of 142-, 145-, and 148-bp in length were most abundant in the amplicons, and most sequences (>92%) belonged to cyanophages. Additionally, different sequencing depths resulted in different diversity estimates of the viral community. Operational taxonomic units obtained from deep sequencing of the MCP gene covered the majority of those obtained from shallow sequencing, suggesting that deep sequencing exhibited a more complete picture of cyanophage community than shallow sequencing. Our results also revealed a wide geographic distribution of marine myocyanophages, i.e., higher dissimilarities of the myocyanophage communities corresponded with the larger distances between the sampling sites. Collectively, this study suggests that the newly designed primer pair can be effectively used to study the community and diversity of myocyanophage from different environments, and the high-throughput sequencing represents a good method to understand viral diversity.

Co-existence of freshwater and marine T4-like myoviruses in a typical subtropical estuary

Viruses are the most abundant biological entities on Earth and play an important role in microbial community dynamics and biogeochemical cycling, yet their ecological characteristics in estuarine ecosystems are unclear. Here, virioplankton communities in a typical subtropical estuary, the Jiulong River estuary (JRE) in China, were investigated. The abundance of virioplankton ranged from 1.01 ± 0.05 × 107 to 1.62 ± 0.09 × 107 particles mL-1 in JRE, and the population size of viruses was correlated with temperature and nutrient levels. Three tailed viral morphotypes (myovirus, siphovirus and podovirus) were observed. Phylogenetic analysis showed that most of the g23 sequences in the JRE fell into three previously established groups (Marine, Paddy and Lake Groups) and two potential Estuary Groups. This demonstrates the co-existence of typical freshwater and marine T4-like myoviruses in the estuarine ecosystem, suggesting the movement of viruses and their hosts among biomes. Additionally, the spatial variation of g23 sequences suggests a geographic distribution pattern of T4-like myoviruses in the JRE, which might be shaped by the environmental gradient and/or their host distribution. These results provide valuable insights into the abundance, diversity and distribution patterns of virioplankton, as well as the factors influencing them, in subtropical estuarine ecosystems.

Assessing the diversity of the g23 gene of T4-like bacteriophages from Lake Baikal with high-throughput sequencing

Based on second generation sequencing (MiSeq platform, Illumina), we determined the genetic diversity of T4-like bacteriophages of the family Myoviridae by analysing fragments of the major capsid protein gene g23 in the plankton of Lake Baikal. The sampling depth in our study was significantly higher than in those obtained by the Sanger method before. We obtained 33 701 sequences of the g23 gene fragments, 141 operational taxonomic units (OTUs) of which were identified. 86 OTUs (60.9%) had the closest relatives from lakes Bourget and Annecy, and 28 OTUs (19.8%) had the highest identity with the Baikal g23 clones, which had been previously identified in the northern and southern basins of the lake by the Sanger method. The remaining OTUs were similar to the clones from other ecosystems. We showed a high genetic diversity of T4-type bacteriophages and a genetic difference with the phage communities from other ecosystems.

Astrovirology: Viruses at Large in the Universe

Viruses are the most abundant biological entities on modern Earth. They are highly diverse both in structure and genomic sequence, play critical roles in evolution, strongly influence terran biogeochemistry, and are believed to have played important roles in the origin and evolution of life. However, there is yet very little focus on viruses in astrobiology. Viruses arguably have coexisted with cellular life-forms since the earliest stages of life, may have been directly involved therein, and have profoundly influenced cellular evolution. Viruses are the only entities on modern Earth to use either RNA or DNA in both single- and double-stranded forms for their genetic material and thus may provide a model for the putative RNA-protein world. With this review, we hope to inspire integration of virus research into astrobiology and also point out pressing unanswered questions in astrovirology, particularly regarding the detection of virus biosignatures and whether viruses could be spread extraterrestrially. We present basic virology principles, an inclusive definition of viruses, review current virology research pertinent to astrobiology, and propose ideas for future astrovirology research foci. Key Words: Astrobiology-Virology-Biosignatures-Origin of life-Roadmap. Astrobiology 18, 207-223.

MARVEL, a Tool for Prediction of Bacteriophage Sequences in Metagenomic Bins

Here we present MARVEL, a tool for prediction of double-stranded DNA bacteriophage sequences in metagenomic bins. MARVEL uses a random forest machine learning approach. We trained the program on a dataset with 1,247 phage and 1,029 bacterial genomes, and tested it on a dataset with 335 bacterial and 177 phage genomes. We show that three simple genomic features extracted from contig sequences were sufficient to achieve a good performance in separating bacterial from phage sequences: gene density, strand shifts, and fraction of significant hits to a viral protein database. We compared the performance of MARVEL to that of VirSorter and VirFinder, two popular programs for predicting viral sequences. Our results show that all three programs have comparable specificity, but MARVEL achieves much better performance on the recall (sensitivity) measure. This means that MARVEL should be able to identify many more phage sequences in metagenomic bins than heretofore has been possible. In a simple test with real data, containing mostly bacterial sequences, MARVEL classified 58 out of 209 bins as phage genomes; other evidence suggests that 57 of these 58 bins are novel phage sequences. MARVEL is freely available at https://github.com/LaboratorioBioinformatica/MARVEL.

Viruses in Soil Ecosystems: An Unknown Quantity Within an Unexplored Territory

Viral abundance in soils can range from below detection limits in hot deserts to over 1 billion per gram in wetlands. Abundance appears to be strongly influenced by water availability and temperature, but a lack of informational standards creates difficulties for cross-study analysis. Soil viral diversity is severely underestimated and undersampled, although current measures of viral richness are higher for soils than for aquatic ecosystems. Both morphometric and metagenomic analyses have raised questions about the prevalence of nontailed, ssDNA viruses in soils. Soil is complex and critically important to terrestrial biodiversity and human civilization, but impacts of viral activities on soil ecosystem services are poorly understood. While information from aquatic systems and medical microbiology suggests the potential for viral influences on nutrient cycles, food web interactions, gene transfer, and other key processes in soils, very few empirical data are available. To understand the soil virome, much work remains.

Benchmarking viromics: an in silico evaluation of metagenome-enabled estimates of viral community composition and diversity

Background

Viral metagenomics (viromics) is increasingly used to obtain uncultivated viral genomes, evaluate community diversity, and assess ecological hypotheses. While viromic experimental methods are relatively mature and widely accepted by the research community, robust bioinformatics standards remain to be established. Here we used in silico mock viral communities to evaluate the viromic sequence-to-ecological-inference pipeline, including (i) read pre-processing and metagenome assembly, (ii) thresholds applied to estimate viral relative abundances based on read mapping to assembled contigs, and (iii) normalization methods applied to the matrix of viral relative abundances for alpha and beta diversity estimates.

Results

Tools specifically designed for metagenomes, specifically metaSPAdes, MEGAHIT, and IDBA-UD, were the most effective at assembling viromes. Read pre-processing, such as partitioning, had virtually no impact on assembly output, but may be useful when hardware is limited. Viral populations with 2–5 × coverage typically assembled well, whereas lesser coverage led to fragmented assembly. Strain heterogeneity within populations hampered assembly, especially when strains were closely related (average nucleotide identity, or ANI ≥97%) and when the most abundant strain represented <50% of the population. Viral community composition assessments based on read recruitment were generally accurate when the following thresholds for detection were applied: (i) ≥10 kb contig lengths to define populations, (ii) coverage defined from reads mapping at ≥90% identity, and (iii) ≥75% of contig length with ≥1 × coverage. Finally, although data are limited to the most abundant viruses in a community, alpha and beta diversity patterns were robustly estimated (±10%) when comparing samples of similar sequencing depth, but more divergent (up to 80%) when sequencing depth was uneven across the dataset. In the latter cases, the use of normalization methods specifically developed for metagenomes provided the best estimates.

Conclusions

These simulations provide benchmarks for selecting analysis cut-offs and establish that an optimized sample-to-ecological-inference viromics pipeline is robust for making ecological inferences from natural viral communities. Continued development to better accessing RNA, rare, and/or diverse viral populations and improved reference viral genome availability will alleviate many of viromics remaining limitations.

Phylogenetic Diversity of T4-Type Phages in Sediments from the Subtropical Pearl River Estuary

Viruses are an abundant and active component of marine sediments and play a significant role in microbial ecology and biogeochemical cycling at local and global scales. To obtain a better understanding of the ecological characteristics of the viriobenthos, the abundance and morphology of viruses and the diversity and community structure of T4-type phages were systematically investigated in the surface sediments of the subtropical Pearl River Estuary (PRE). Viral abundances ranged from 4.49 × 10⁸ to 11.7 × 10⁸ viruses/g and prokaryotic abundances ranged from 2.63 × 10⁸ to 9.55 × 10⁸ cells/g, and both decreased from freshwater to saltwater. Diverse viral morphotypes, including tailed, spherical, filamentous, and rod-shaped viruses, were observed using transmission electron microscopy. Analysis of the major capsid gene (g23) indicated that the sediment T4-type phages were highly diverse and, similar to the trend in viral abundances, their diversity decreased as the salinity increased. Phylogenetic analysis suggested that most of the g23 operational taxonomic units were affiliated with marine, paddy soil, and lake groups. The T4-type phage communities in freshwater and saltwater sediments showed obvious differences, which were related to changes in the Pearl River discharge. The results of this study demonstrated both allochthonous and autochthonous sources of the viral community in the PRE sediments and the movement of certain T4-type viral groups between the freshwater and saline water biomes.

Suppression of Enteric Bacteria by Bacteriophages: Importance of Phage Polyvalence in the Presence of Soil Bacteria

Bacteriophages are widely recognized for their importance in microbial ecology and bacterial control. However, little is known about how phage polyvalence (i.e., broad host range) affects bacterial suppression and interspecies competition in environments harboring enteric pathogens and soil bacteria. Here we compare the efficacy of polyvalent phage PEf1 versus coliphage T4 in suppressing a model enteric bacterium (E. coli K-12) in mixtures with soil bacteria (Pseudomonas putida F1 and Bacillus subtilis 168). Although T4 was more effective than PEf1 in infecting E. coli K-12 in pure cultures, PEf1 was 20-fold more effective in suppressing E. coli under simulated multispecies biofilm conditions because polyvalence enhanced PEf1 propagation in P. putida. In contrast, soil bacteria do not propagate coliphages and hindered T4 diffusion through the biofilm. Similar tests were also conducted under planktonic conditions to discern how interspecies competition contributes to E. coli suppression without the confounding effects of restricted phage diffusion. Significant synergistic suppression was observed by the combined effects of phages plus competing bacteria. T4 was slightly more effective in suppressing E. coli in these planktonic mixed cultures, even though PEf1 reached higher concentrations by reproducing also in P. putida (7.2 ± 0.4 vs 6.0 ± 1.0 log₁₀PFU/mL). Apparently, enhanced suppression by higher PEf1 propagation was offset by P. putida lysis, which decreased stress from interspecies competition relative to incubations with T4. In similar planktonic tests with more competing soil bacteria species, P. putida lysis was less critical in mitigating interspecies competition and PEf1 eliminated E. coli faster than T4 (36 vs 42 h). Overall, this study shows that polyvalent phages can propagate in soil bacteria and significantly enhance suppression of co-occurring enteric species.

The use of informativity in the development of robust viromics-based examinations

Metagenomics-based studies have provided insight into many of the complex microbial communities responsible for maintaining life on this planet. Sequencing efforts often uncover novel genetic content; this is most evident for phage communities, in which upwards of 90% of all sequences exhibit no similarity to any sequence in current data repositories. For the small fraction that can be identified, the top BLAST hit is generally posited as being representative of a viral taxon present in the sample of origin. Homology-based classification, however, can be misleading as sequence repositories capture but a small fraction of phage diversity. Furthermore, lateral gene transfer is pervasive within phage communities. As such, the presence of a particular gene may not be indicative of the presence of a particular viral species. Rather, it is just that: an indication of the presence of a specific gene. To circumvent this limitation, we have developed a new method for the analysis of viral metagenomic datasets. BLAST hits are weighted, integrating the sequence identity and length of alignments as well as a taxonomic signal, such that each gene is evaluated with respect to its information content. Through this quantifiable metric, predictions of viral community structure can be made with confidence. As a proof-of-concept, the approach presented here was implemented and applied to seven freshwater viral metagenomes. While providing a robust method for evaluating viral metagenomic data, the tool is versatile and can easily be customized to investigations of any environment or biome.

Ecological dynamics and co-occurrence among marine phytoplankton, bacteria and myoviruses shows microdiversity matters

Numerous ecological processes, such as bacteriophage infection and phytoplankton-bacterial interactions, often occur via strain-specific mechanisms. Therefore, studying the causes of microbial dynamics should benefit from highly resolving taxonomic characterizations. We sampled daily to weekly over 5 months following a phytoplankton bloom off Southern California and examined the extent of microdiversity, that is, significant variation within 99% sequence similarity clusters, operational taxonomic units (OTUs), of bacteria, archaea, phytoplankton chloroplasts (all via 16S or intergenic spacer (ITS) sequences) and T4-like-myoviruses (via g23 major capsid protein gene sequence). The extent of microdiversity varied between genes (ITS most, g23 least) and only temporally common taxa were highly microdiverse. Overall, 60% of taxa exhibited microdiversity; 59% of these had subtypes that changed significantly as a proportion of the parent taxon, indicating ecologically distinct taxa. Pairwise correlations between prokaryotes and myoviruses or phytoplankton (for example, highly microdiverse Chrysochromulina sp.) improved when using single-base variants. Correlations between myoviruses and SAR11 increased in number (172 vs 9, Spearman>0.65) and became stronger (0.61 vs 0.58, t-test: P<0.001) when using SAR11 ITS single-base variants vs OTUs. Whole-community correlation between SAR11 and myoviruses was much improved when using ITS single-base variants vs OTUs, with Mantel rho=0.49 vs 0.27; these results are consistent with strain-specific interactions. Mantel correlations suggested >1 μm (attached/large) prokaryotes are a major myovirus source. Consideration of microdiversity improved observation of apparent host and virus networks, and provided insights into the ecological and evolutionary factors influencing the success of lineages, with important implications to ecosystem resilience and microbial function.