Phage puppet masters of the marine microbial realm

Influence of phytoplankton, bacteria and viruses on nutrient supply in tropical waters

Diel investigations of water environments are one means to holistically understand the dynamics and functional roles of phytoplankton, bacteria and viruses in these ecosystems. They have the potential to substantially impact carbon (C), nitrogen (N) and phosphorus (P) biogeochemistry through their respective roles. This study characterizes the phytoplankton, bacteria and virus communities and the elemental composition of various C, N and P nutrients flow over three diel cycles in tropical urban lake. Our results show that ratios of C:N:P fluctuated strongly from the lack of dissolved organic phosphorus (DOP) and PO4. Specifically, green algae peaked during day time and exudate dissolved organic matter (DOM) that strongly modulate dissolved organic carbon (DOC):DOP ratio to diel DOP limitation. Multiple linear regression and Stella modelling emphasize the roles of viruses together with Synechococcus as important nutrient recyclers of NH4 and PO4 in nutrients-limited waters. Respective normalised surface PO4 and combined surface and bottom NH4 concentration selected both viruses and Synechococcus as important drivers. Process model of N and P biogeochemical cycles can achieve 69% and 57% similar to observed concentration of NH4 and PO4, respectively. A short latent period of 9 hr was calculated, in addition to the calibrated high infectivity of viruses to Synechococcus. Taken together, the rapid turn-over between Synechococcus and viruses has biogeochemical significance, where the rapid recycling of essential nutrients allows for shortcuts in the N and P cycle, supporting a wide range of microbes.

vClean: assessing virus sequence contamination in viral genomes

Recent advancements in viral metagenomics and single-virus genomics have improved our ability to obtain the draft genomes of environmental viruses. However, these methods can introduce virus sequence contaminations into viral genomes when short, fragmented partial sequences are present in the assembled contigs. These contaminations can lead to incorrect analyses; however, practical detection tools are lacking. In this study, we introduce vClean, a novel automated tool that detects contaminations in viral genomes. By applying machine learning to the nucleotide sequence features and gene patterns of the input viral genome, vClean could identify contaminations. Specifically, for tailed double-stranded DNA phages, we attempted accurate predictions by defining single-copy-like genes and counting their duplications. We evaluated the performance of vClean using simulated datasets derived from complete reference genomes, achieving a binary accuracy of 0.932. When vClean was applied to 4693 genomes of medium or higher quality derived from public ocean metagenomic data, 1604 genomes (34.2%) were identified as contaminated. We also demonstrated that vClean can detect contamination in single-virus genome data obtained from river water. vClean provides a new benchmark for quality control of environmental viral genomes and has the potential to become an essential tool for environmental viral genome analysis.

To kill or to piggyback: Switching of viral lysis-lysogeny strategies depending on host dynamics

Viruses wield significant influence over microbial communities and ecosystem function in marine environments. However, the selection of viral life strategies and their impacts on microbial communities remains enigmatic. In this study, we utilized a large-scale macrocosm, established using water samples from a marine coastal region, to enable community-level investigation. Through a prolonged incubation experiment, we aimed to clarify the ramifications of lytic and lysogenic viral activities on microbial community dynamics. We observed a continuous succession in bacterial abundance, growth rate, and community diversity, tightly linked with time series switching between viral lysis and lysogeny. Elevated lytic viral production notably fostered greater bacterial diversity, whereas increased lysogenic viral production corresponded to bacterial communities characterized by heightened abundance and growth rate but reduced diversity. Moreover, discernible shifts in bacterial community compositions, associated with different abundant bacterial taxa, were synchronized with pronounced transitions between viral lysis and lysogeny. Notably, the switch from lysogeny to lysis facilitated the proliferation of initially rare bacterial populations. Our findings suggest that the Kill-the-Winner and Piggyback-the-Winner hypotheses, both elucidating dynamic patterns in virus-host interactions, can synergistically demonstrate the pivotal role of viruses in regulating microbial communities via the lysis-lysogeny switch in marine environments.

Unravelling viral ecology and evolution over 20 years in a freshwater lake

As freshwater lakes undergo rapid anthropogenic change, long-term studies reveal key microbial dynamics, evolutionary shifts and biogeochemical interactions, yet the vital role of viruses remains overlooked. Here, leveraging a 20 year time series from Lake Mendota, WI, USA, we characterized 1.3 million viral genomes across time, seasonality and environmental factors. Double-stranded DNA phages from the class Caudoviricetes dominated the community. We identified 574 auxiliary metabolic gene families representing over 140,000 auxiliary metabolic genes, including important genes such as psbA (photosynthesis), pmoC (methane oxidation) and katG (hydrogen peroxide decomposition), which were consistently present and active across decades and seasons. Positive associations and niche differentiation between virus-host pairs, including keystone Cyanobacteria, methanotrophs and Nanopelagicales, emerged during seasonal changes. Inorganic carbon and ammonium influenced viral abundances, underscoring viral roles in both 'top-down' and 'bottom-up' interactions. Evolutionary processes favoured fitness genes, reduced genomic heterogeneity and dominant sub-populations. This study transforms understanding of viral ecology and evolution in Earth's microbiomes.

Mapping the metagenomic diversity of the multi-kingdom glacier-fed stream microbiome

Glacier-fed streams (GFS) feature among Earth's most extreme aquatic ecosystems marked by pronounced oligotrophy and environmental fluctuations. Microorganisms mainly organize in biofilms within them, but how they cope with such conditions is unknown. Here, leveraging 156 metagenomes from the Vanishing Glaciers project obtained from sediment samples in GFS from 9 mountains ranges, we report thousands of metagenome-assembled genomes (MAGs) encompassing prokaryotes, algae, fungi and viruses, that shed light on biotic interactions within glacier-fed stream biofilms. A total of 2,855 bacterial MAGs were characterized by diverse strategies to exploit inorganic and organic energy sources, in part via functional redundancy and mixotrophy. We show that biofilms probably become more complex and switch from chemoautotrophy to heterotrophy as algal biomass increases in GFS owing to glacier shrinkage. Our MAG compendium sheds light on the success of microbial life in GFS and provides a resource for future research on a microbiome potentially impacted by climate change.

Abundance measurements reveal the balance between lysis and lysogeny in the human gut microbiome

The human gut contains diverse communities of bacteriophage, whose interactions with the broader microbiome and potential roles in human health are only beginning to be uncovered. Here, we combine multiple types of data to quantitatively estimate gut phage population dynamics and lifestyle characteristics in human subjects. Unifying results from previous studies, we show that an average human gut contains a low ratio of phage particles to bacterial cells (~1:100), but a much larger ratio of phage genomes to bacterial genomes (~4:1), implying that most gut phage are effectively temperate (e.g., integrated prophage, phage-plasmids, etc.). By integrating imaging and sequencing data with a generalized model of temperate phage dynamics, we estimate that phage induction and lysis occurs at a low average rate (~0.001-0.01 per bacterium per day), imposing only a modest fitness burden on their bacterial hosts. Consistent with these estimates, we find that the phage composition of a diverse synthetic community in gnotobiotic mice can be quantitatively predicted from bacterial abundances alone, while still exhibiting phage diversity comparable to native human microbiomes. These results provide a foundation for interpreting existing and future studies on links between the gut virome and human health.

Inferring strain-level mutational drivers of phage-bacteria interaction phenotypes arising during coevolutionary dynamics

The enormous diversity of bacteriophages and their bacterial hosts presents a significant challenge to predict which phages infect a focal set of bacteria. Infection is largely determined by complementary-and largely uncharacterized-genetics of adsorption, injection, cell take-over, and lysis. Here we present a machine learning approach to predict phage-bacteria interactions trained on genome sequences of and phenotypic interactions among 51 Escherichia coli strains and 45 phage λ strains that coevolved in laboratory conditions for 37 days. Leveraging multiple inference strategies and without a priori knowledge of driver mutations, this framework predicts both who infects whom and the quantitative levels of infections across a suite of 2,295 potential interactions. We found that the most effective approach inferred interaction phenotypes from independent contributions from phage and bacteria mutations, accurately predicting 86% of interactions while reducing the relative error in the estimated strength of the infection phenotype by 40%. Feature selection revealed key phage λ and Escherchia coli mutations that have a significant influence on the outcome of phage-bacteria interactions, corroborating sites previously known to affect phage λ infections, as well as identifying mutations in genes of unknown function not previously shown to influence bacterial resistance. The method's success in recapitulating strain-level infection outcomes arising during coevolutionary dynamics may also help inform generalized approaches for imputing genetic drivers of interaction phenotypes in complex communities of phage and bacteria.

Phage-induced disturbance of a marine sponge microbiome

BACKGROUND

Bacteriophages are known modulators of community composition and activity in environmental and host-associated microbiomes. However, the impact single phages have on bacterial community dynamics under viral predation, the extent and duration of their effect, are not completely understood. In this study, we combine morphological and genomic characterization of a novel marine phage, isolated from the Baltic sponge Halichondria panicea, and report on first attempts of controlled phage-manipulation of natural sponge-associated microbiomes.

RESULTS

We used culture-based and culture-independent (16S rRNA gene amplicon sequencing) methods to investigate bacterial community composition and dynamics in sponge microbiomes with and without the addition of phages. Upon application of a novel Maribacter specialist phage Panino under controlled conditions, we were able to detect community-wide shifts in the microbiome composition and load after 72 h. While bacterial community composition became more dissimilar over time in the presence of phages, species evenness and richness were maintained. Upon phage exposure, we observed the loss of several low-abundance constituent taxa of the resident microbiota, while other originally underrepresented taxa increased. Virulent phages likely induce community-wide disturbances, evident in changes in the total sponge microbial profile by specific elimination of constituent taxa, which leads to an increase in bacterial abundance of opportunistic taxa, such as the genera Vibrio, Pseudoalteromonas, and Photobacterium.

CONCLUSIONS

Our findings suggest that sponge microbiome diversity and, by extension, its resilience depend on the maintenance of resident bacterial community members, irrespective of their abundance. Phage-induced disturbances can significantly alter community structure by promoting the growth of opportunistic bacteria like Vibrio and shifting the microbiome to a dysbiotic state. These insights highlight the role of bacteriophages in shaping microbiome dynamics and underscore the potential for phage application in managing bacterial community composition in marine host-associated environments.

Inferring strain-level mutational drivers of phage-bacteria interaction phenotypes arising during coevolutionary dynamics

The enormous diversity of bacteriophages and their bacterial hosts presents a significant challenge to predict which phages infect a focal set of bacteria. Infection is largely determined by complementary - and largely uncharacterized - genetics of adsorption, injection, cell take-over and lysis. Here we present a machine learning approach to predict phage-bacteria interactions trained on genome sequences of and phenotypic interactions amongst 51 Escherichia coli strains and 45 phage λ strains that coevolved in laboratory conditions for 37 days. Leveraging multiple inference strategies and without a priori knowledge of driver mutations, this framework predicts both who infects whom and the quantitative levels of infections across a suite of 2,295 potential interactions. We found that the most effective approach inferred interaction phenotypes from independent contributions from phage and bacteria mutations, accurately predicting 86 % of interactions while reducing the relative error in the estimated strength of the infection phenotype by 40 % . Feature selection revealed key phage λ and E. coli mutations that have a significant influence on the outcome of phage-bacteria interactions, corroborating sites previously known to affect phage λ infections, as well as identifying mutations in genes of unknown function not previously shown to influence bacterial resistance. The method's success in recapitulating strain-level infection outcomes arising during coevolutionary dynamics may also help inform generalized approaches for imputing genetic drivers of interaction phenotypes in complex communities of phage and bacteria.

Mitomycin C eliminates cyanobacterial transcription without detectable lysogen induction in a Microcystis -dominated bloom in Lake Erie

Although evidence indicates that viruses are important in the ecology of Microcystis spp., many questions remain. For example, how does Microcystis exist at high, bloom-associated cell concentrations in the presence of viruses that infect it? The phenomenon of lysogeny and associated homoimmunity offer possible explanations to this question. Virtually nothing is known about lysogeny in Microcystis , but a metatranscriptomic study suggests that widespread, transient lysogeny is active during blooms. These observations lead us to posit that lysogeny is important in modulating Microcystis blooms. Using a classic mitomycin C-based induction study, we tested for lysogeny in a Microcystis -dominated community in Lake Erie in 2019. Treated communities were incubated with 1 mg L -1 mitomycin C for 48 h alongside unamended controls. We compared direct counts of virus-like-particles (VLPs) and examined community transcription for active infection by cyanophage. Mitomycin C treatment did not increase VLP count. Mitomycin C effectively eliminated transcription in the cyanobacterial community, while we detected no evidence of induction. Metatranscriptomic analysis demonstrated that the standard protocol of 1 mg L -1 was highly-toxic to the cyanobacterial population, which likely inhibited induction of any prophage present. Follow-up lab studies indicated that 0.1 mg L -1 may be more appropriate for use in freshwater cyanobacterial studies. These findings will guide future efforts to detect lysogeny in Microcystis blooms.

Importance

Harmful algal blooms dominated by Microcystis spp. occur throughout the world's freshwater ecosystems leading to detrimental effects on ecosystem services that are well documented. After decades of research, the scientific community continues to struggle to understand the ecology of Microcystis blooms. The phenomenon of lysogeny offers an attractive, potential explanation to several ecological questions surrounding blooms. However, almost nothing is known about lysogeny in Microcystis . We attempted to investigate lysogeny in a Microcystis bloom in Lake Erie and found that the standard protocols used to study lysogeny in aquatic communities are inappropriate for use in Microcystis studies, and perhaps freshwater cyanobacterial studies more broadly. This work can be used to design better methods to study the viral ecology of Microcystis blooms.

Diverse microviruses circulating in invertebrates within a lake ecosystem

Microviruses are single-stranded DNA bacteriophages and members of the highly diverse viral family Microviridae. Microviruses have a seemingly ubiquitous presence across animal gut microbiomes and other global environmental ecosystems. Most of the studies on microvirus diversity so far have been associated with vertebrate gut viromes. In this study, we investigate the less explored invertebrate microviruses in a freshwater ecosystem. We analysed microviruses from invertebrates in the Chironomidae, Gastropoda, Odonata, Sphaeriidae, Unionidae clades, as well as from water and benthic sediment sampled from a lake ecosystem in New Zealand. Using gene-sharing networks and an expanded framework of informal and proposed microvirus subfamilies, the 463 distinct microvirus genomes identified in this study were grouped as follows: 382 genomes in the Gokushovirinae subfamily and 47 in the Pichovirinae subfamily clade, 18 belonging to Group D, 3 belonging to the proposed Alpavirinae subfamily clade, 1 belonging to the proposed Occultatumvirinae/Tainavirinae subfamilies clade and 12 belonging to an undefined viral cluster VC 1. Inverse associations of microviruses were noted between environmental benthic sediment samples and the Odonata group, while 'defended' invertebrates in the Gastropoda, Sphaeriidae and Unionidae groups showed correlative associations in the principal coordinate analysis of unique microvirus genomes (each genome sharing <98% genome-wide pairwise identity with each other) across sample types. This study expands the known diversity of microviruses and highlights the diversity of these relatively poorly classified bacteriophages.

Time Series Data Provide Insights into the Evolution and Abundance of One of the Most Abundant Viruses in the Marine Virosphere: The Uncultured Pelagiphages vSAG 37-F6

Viruses play a pivotal role in ecosystems by influencing biochemical cycles and impacting the structure and evolution of their host cells. The widespread pelagiphages infect Pelagibacter spp., the most abundant marine microbe on Earth, and thus play a significant role in carbon transformation through the viral shunt. Among these viruses, the uncultured lytic pelagiphage vSAG 37-F6, uncovered by single-virus genomics, is likely the most numerous virus in the ocean. While previous research has delved into the diversity and spatial distribution of vSAG 37-F6, there is still a gap in understanding its temporal dynamics, hindering our insight into its ecological impact. We explored the temporal dynamics of vSAG 37-F6, assessing periodic fluctuations in abundance and evolutionary patterns using long- and short-term data series. In the long-term series (7 years), metagenomics showed negative selection acting on all viral genes, with a highly conserved overall diversity over time composed of a pool of yearly emergent, highly similar novel strains that exhibited a seasonal abundance pattern with two peaks during winter and fall and a decrease in months with higher UV radiation. Most non-synonymous polymorphisms occurred in structural viral proteins located in regions with low conformational restrictions, suggesting that many of the viral genes of this population are highly purified over its evolution. At the fine-scale resolution (24 h time series), combining digital PCR and metagenomics, we identified two peaks of cellular infection for the targeted vSAG 37-F6 viral strain (up to approximately 103 copies/ng of prokaryotic DNA), one before sunrise and the second shortly after midday. Considering the high number of co-occurring strains of this microdiverse virus, the abundance values at the species or genus level could be orders of magnitudes higher. These findings represent a significant advancement in understanding the dynamics of the potentially most abundant oceanic virus, providing valuable insights into ecologically relevant marine viruses.

MVP: a modular viromics pipeline to identify, filter, cluster, annotate, and bin viruses from metagenomes

While numerous computational frameworks and workflows are available for recovering prokaryote and eukaryote genomes from metagenome data, only a limited number of pipelines are designed specifically for viromics analysis. With many viromics tools developed in the last few years alone, it can be challenging for scientists with limited bioinformatics experience to easily recover, evaluate quality, annotate genes, dereplicate, assign taxonomy, and calculate relative abundance and coverage of viral genomes using state-of-the-art methods and standards. Here, we describe Modular Viromics Pipeline (MVP) v.1.0, a user-friendly pipeline written in Python and providing a simple framework to perform standard viromics analyses. MVP combines multiple tools to enable viral genome identification, characterization of genome quality, filtering, clustering, taxonomic and functional annotation, genome binning, and comprehensive summaries of results that can be used for downstream ecological analyses. Overall, MVP provides a standardized and reproducible pipeline for both extensive and robust characterization of viruses from large-scale sequencing data including metagenomes, metatranscriptomes, viromes, and isolate genomes. As a typical use case, we show how the entire MVP pipeline can be applied to a set of 20 metagenomes from wetland sediments using only 10 modules executed via command lines, leading to the identification of 11,656 viral contigs and 8,145 viral operational taxonomic units (vOTUs) displaying a clear beta-diversity pattern. Further, acting as a dynamic wrapper, MVP is designed to continuously incorporate updates and integrate new tools, ensuring its ongoing relevance in the rapidly evolving field of viromics. MVP is available at https://gitlab.com/ccoclet/mvp and as versioned packages in PyPi and Conda.IMPORTANCEThe significance of our work lies in the development of Modular Viromics Pipeline (MVP), an integrated and user-friendly pipeline tailored exclusively for viromics analyses. MVP stands out due to its modular design, which ensures easy installation, execution, and integration of new tools and databases. By combining state-of-the-art tools such as geNomad and CheckV, MVP provides high-quality viral genome recovery and taxonomy and host assignment, and functional annotation, addressing the limitations of existing pipelines. MVP's ability to handle diverse sample types, including environmental, human microbiome, and plant-associated samples, makes it a versatile tool for the broader microbiome research community. By standardizing the analysis process and providing easily interpretable results, MVP enables researchers to perform comprehensive studies of viral communities, significantly advancing our understanding of viral ecology and its impact on various ecosystems.

Diversity and ecology of microbial sulfur metabolism

Sulfur plays a pivotal role in interactions within the atmosphere, lithosphere, pedosphere, hydrosphere and biosphere, and the functioning of living organisms. In the Earth's crust, mantle, and atmosphere, sulfur undergoes geochemical transformations due to natural and anthropogenic factors. In the biosphere, sulfur participates in the formation of amino acids, proteins, coenzymes and vitamins. Microorganisms in the biosphere are crucial for cycling sulfur compounds through oxidation, reduction and disproportionation reactions, facilitating their bioassimilation and energy generation. Microbial sulfur metabolism is abundant in both aerobic and anaerobic environments and is interconnected with biogeochemical cycles of important elements such as carbon, nitrogen and iron. Through metabolism, competition or cooperation, microorganisms metabolizing sulfur can drive the consumption of organic carbon, loss of fixed nitrogen and production of climate-active gases. Given the increasing significance of sulfur metabolism in environmental alteration and the intricate involvement of microorganisms in sulfur dynamics, a timely re-evaluation of the sulfur cycle is imperative. This Review explores our understanding of microbial sulfur metabolism, primarily focusing on the transformations of inorganic sulfur. We comprehensively overview the sulfur cycle in the face of rapidly changing ecosystems on Earth, highlighting the importance of microbially-mediated sulfur transformation reactions across different environments, ecosystems and microbiomes.

Viromes vs. mixed community metagenomes: choice of method dictates interpretation of viral community ecology

BACKGROUND

Viruses, the majority of which are uncultivated, are among the most abundant biological entities on Earth. From altering microbial physiology to driving community dynamics, viruses are fundamental members of microbiomes. While the number of studies leveraging viral metagenomics (viromics) for studying uncultivated viruses is growing, standards for viromics research are lacking. Viromics can utilize computational discovery of viruses from total metagenomes of all community members (hereafter metagenomes) or use physical separation of virus-specific fractions (hereafter viromes). However, differences in the recovery and interpretation of viruses from metagenomes and viromes obtained from the same samples remain understudied.

RESULTS

Here, we compare viral communities from paired viromes and metagenomes obtained from 60 diverse samples across human gut, soil, freshwater, and marine ecosystems. Overall, viral communities obtained from viromes had greater species richness and total viral genome abundances than those obtained from metagenomes, although there were some exceptions. Despite this, metagenomes still contained many viral genomes not detected in viromes. We also found notable differences in the predicted lytic state of viruses detected in viromes vs metagenomes at the time of sequencing. Other forms of variation observed include genome presence/absence, genome quality, and encoded protein content between viromes and metagenomes, but the magnitude of these differences varied by environment.

CONCLUSIONS

Overall, our results show that the choice of method can lead to differing interpretations of viral community ecology. We suggest that the choice of whether to target a metagenome or virome to study viral communities should be dependent on the environmental context and ecological questions being asked. However, our overall recommendation to researchers investigating viral ecology and evolution is to pair both approaches to maximize their respective benefits. Video Abstract.

Critically evaluating the relative importance of phage in shaping microbial community composition

The ubiquity of bacteriophages (phages) and the major evolutionary and ecological impacts they can have on their microbial hosts has resulted in phages often cited as key drivers shaping microbial community composition (the relative abundances of species). However, the evidence for the importance of phages is mixed. Here, we critically review the theory and data exploring the role of phages in communities, identifying the conditions when phages are likely to be important drivers of community composition. At ecological scales, we conclude that phages are often followers rather than drivers of microbial population and community dynamics. While phages can affect strain diversity within species, there is yet to be strong evidence suggesting that fluctuations in species' strains affects community composition.

Strain-resolved de-novo metagenomic assembly of viral genomes and microbial 16S rRNAs

BACKGROUND

Metagenomics is a powerful approach to study environmental and human-associated microbial communities and, in particular, the role of viruses in shaping them. Viral genomes are challenging to assemble from metagenomic samples due to their genomic diversity caused by high mutation rates. In the standard de Bruijn graph assemblers, this genomic diversity leads to complex k-mer assembly graphs with a plethora of loops and bulges that are challenging to resolve into strains or haplotypes because variants more than the k-mer size apart cannot be phased. In contrast, overlap assemblers can phase variants as long as they are covered by a single read.

RESULTS

Here, we present PenguiN, a software for strain resolved assembly of viral DNA and RNA genomes and bacterial 16S rRNA from shotgun metagenomics. Its exhaustive detection of all read overlaps in linear time combined with a Bayesian model to select strain-resolved extensions allow it to assemble longer viral contigs, less fragmented genomes, and more strains than existing assembly tools, on both real and simulated datasets. We show a 3-40-fold increase in complete viral genomes and a 6-fold increase in bacterial 16S rRNA genes.

CONCLUSION

PenguiN is the first overlap-based assembler for viral genome and 16S rRNA assembly from large and complex metagenomic datasets, which we hope will facilitate studying the key roles of viruses in microbial communities. Video Abstract.

Decomposing a San Francisco estuary microbiome using long-read metagenomics reveals species- and strain-level dominance from picoeukaryotes to viruses

Although long-read sequencing has enabled obtaining high-quality and complete genomes from metagenomes, many challenges still remain to completely decompose a metagenome into its constituent prokaryotic and viral genomes. This study focuses on decomposing an estuarine metagenome to obtain a more accurate estimate of microbial diversity. To achieve this, we developed a new bead-based DNA extraction method, a novel bin refinement method, and obtained 150 Gbp of Nanopore sequencing. We estimate that there are ~500 bacterial and archaeal species in our sample and obtained 68 high-quality bins (>90% complete, <5% contamination, ≤5 contigs, contig length of >100 kbp, and all ribosomal and tRNA genes). We also obtained many contigs of picoeukaryotes, environmental DNA of larger eukaryotes such as mammals, and complete mitochondrial and chloroplast genomes and detected ~40,000 viral populations. Our analysis indicates that there are only a few strains that comprise most of the species abundances.

IMPORTANCE

Ocean and estuarine microbiomes play critical roles in global element cycling and ecosystem function. Despite the importance of these microbial communities, many species still have not been cultured in the lab. Environmental sequencing is the primary way the function and population dynamics of these communities can be studied. Long-read sequencing provides an avenue to overcome limitations of short-read technologies to obtain complete microbial genomes but comes with its own technical challenges, such as needed sequencing depth and obtaining high-quality DNA. We present here new sampling and bioinformatics methods to attempt decomposing an estuarine microbiome into its constituent genomes. Our results suggest there are only a few strains that comprise most of the species abundances from viruses to picoeukaryotes, and to fully decompose a metagenome of this diversity requires 1 Tbp of long-read sequencing. We anticipate that as long-read sequencing technologies continue to improve, less sequencing will be needed.

Virus-host interactions predictor (VHIP): Machine learning approach to resolve microbial virus-host interaction networks

Viruses of microbes are ubiquitous biological entities that reprogram their hosts' metabolisms during infection in order to produce viral progeny, impacting the ecology and evolution of microbiomes with broad implications for human and environmental health. Advances in genome sequencing have led to the discovery of millions of novel viruses and an appreciation for the great diversity of viruses on Earth. Yet, with knowledge of only "who is there?" we fall short in our ability to infer the impacts of viruses on microbes at population, community, and ecosystem-scales. To do this, we need a more explicit understanding "who do they infect?" Here, we developed a novel machine learning model (ML), Virus-Host Interaction Predictor (VHIP), to predict virus-host interactions (infection/non-infection) from input virus and host genomes. This ML model was trained and tested on a high-value manually curated set of 8849 virus-host pairs and their corresponding sequence data. The resulting dataset, 'Virus Host Range network' (VHRnet), is core to VHIP functionality. Each data point that underlies the VHIP training and testing represents a lab-tested virus-host pair in VHRnet, from which meaningful signals of viral adaptation to host were computed from genomic sequences. VHIP departs from existing virus-host prediction models in its ability to predict multiple interactions rather than predicting a single most likely host or host clade. As a result, VHIP is able to infer the complexity of virus-host networks in natural systems. VHIP has an 87.8% accuracy rate at predicting interactions between virus-host pairs at the species level and can be applied to novel viral and host population genomes reconstructed from metagenomic datasets.

Soil keystone viruses are regulators of ecosystem multifunctionality

Ecosystem multifunctionality reflects the capacity of ecosystems to simultaneously maintain multiple functions which are essential bases for human sustainable development. Whereas viruses are a major component of the soil microbiome that drive ecosystem functions across biomes, the relationships between soil viral diversity and ecosystem multifunctionality remain under-studied. To address this critical knowledge gap, we employed a combination of amplicon and metagenomic sequencing to assess prokaryotic, fungal and viral diversity, and to link viruses to putative hosts. We described the features of viruses and their potential hosts in 154 soil samples from 29 farmlands and 25 forests distributed across China. Although 4,460 and 5,207 viral populations (vOTUs) were found in the farmlands and forests respectively, the diversity of specific vOTUs rather than overall soil viral diversity was positively correlated with ecosystem multifunctionality in both ecosystem types. Furthermore, the diversity of these keystone vOTUs, despite being 10-100 times lower than prokaryotic or fungal diversity, was a better predictor of ecosystem multifunctionality and more strongly associated with the relative abundances of prokaryotic genes related to soil nutrient cycling. Gemmatimonadota and Actinobacteria dominated the host community of soil keystone viruses in the farmlands and forests respectively, but were either absent or showed a significantly lower relative abundance in that of soil non-keystone viruses. These findings provide novel insights into the regulators of ecosystem multifunctionality and have important implications for the management of ecosystem functioning.

Prokaryotic-virus-encoded auxiliary metabolic genes throughout the global oceans

BACKGROUND

Prokaryotic microbes have impacted marine biogeochemical cycles for billions of years. Viruses also impact these cycles, through lysis, horizontal gene transfer, and encoding and expressing genes that contribute to metabolic reprogramming of prokaryotic cells. While this impact is difficult to quantify in nature, we hypothesized that it can be examined by surveying virus-encoded auxiliary metabolic genes (AMGs) and assessing their ecological context.

RESULTS

We systematically developed a global ocean AMG catalog by integrating previously described and newly identified AMGs and then placed this catalog into ecological and metabolic contexts relevant to ocean biogeochemistry. From 7.6 terabases of Tara Oceans paired prokaryote- and virus-enriched metagenomic sequence data, we increased known ocean virus populations to 579,904 (up 16%). From these virus populations, we then conservatively identified 86,913 AMGs that grouped into 22,779 sequence-based gene clusters, 7248 (~ 32%) of which were not previously reported. Using our catalog and modeled data from mock communities, we estimate that ~ 19% of ocean virus populations carry at least one AMG. To understand AMGs in their metabolic context, we identified 340 metabolic pathways encoded by ocean microbes and showed that AMGs map to 128 of them. Furthermore, we identified metabolic "hot spots" targeted by virus AMGs, including nine pathways where most steps (≥ 0.75) were AMG-targeted (involved in carbohydrate, amino acid, fatty acid, and nucleotide metabolism), as well as other pathways where virus-encoded AMGs outnumbered cellular homologs (involved in lipid A phosphates, phosphatidylethanolamine, creatine biosynthesis, phosphoribosylamine-glycine ligase, and carbamoyl-phosphate synthase pathways).

CONCLUSIONS

Together, this systematically curated, global ocean AMG catalog and analyses provide a valuable resource and foundational observations to understand the role of viruses in modulating global ocean metabolisms and their biogeochemical implications. Video Abstract.

Metatranscriptomic response of deep ocean microbial populations to infusions of oil and/or synthetic chemical dispersant

Oil spills are a frequent perturbation to the marine environment that has rapid and significant impacts on the local microbiome. Previous studies have shown that exposure to synthetic dispersant alone did not enhance heterotrophic microbial activity or oxidation rates of specific hydrocarbon components but increased the abundance of some taxa (e.g., Colwellia). In contrast, exposure to oil, but not dispersants, increased the abundance of other taxa (e.g., Marinobacter) and stimulated hydrocarbon oxidation rates. Here, we advance these findings by interpreting metatranscriptomic data from this experiment to explore how and why specific components of the microbial community responded to distinct organic carbon exposure regimes. Dispersant alone was selected for a unique community and for dominant organisms that reflected treatment- and time-dependent responses. Dispersant amendment also led to diverging functional profiles among the different treatments. Similarly, oil alone was selected for a community that was distinct from treatments amended with dispersants. The presence of oil and dispersants with added nutrients led to substantial differences in microbial responses, likely suggesting increased fitness driven by the presence of additional inorganic nutrients. The oil-only additions led to a marked increase in the expression of phages, prophages, transposable elements, and plasmids (PPTEPs), suggesting that aspects of microbial community response to oil are driven by the "mobilome," potentially through viral-associated regulation of metabolic pathways in ciliates and flagellates that would otherwise throttle the microbial community through grazing.IMPORTANCEMicrocosm experiments simulated the April 2010 Deepwater Horizon oil spill by applying oil and synthetic dispersants (Corexit EC9500A and EC9527A) to deep ocean water samples. The exposure regime revealed severe negative alterations in the treatments' heterotrophic microbial activity and hydrocarbon oxidation rates. We expanded these findings by exploring metatranscriptomic signatures of the microbial communities during the chemical amendments in the microcosm experiments. Here we report how dominant organisms were uniquely associated with treatment- and time-dependent trajectories during the exposure regimes; nutrient availability was a significant factor in driving changes in metatranscriptomic responses. Remarkable signals associated with PPTEPs showed the potential role of mobilome and viral-associated survival responses. These insights underscore the time-dependent environmental perturbations of fragile marine environments under oil and anthropogenic stress.

Accounting for cellular-level variation in lysis: implications for virus-host dynamics

Viral impacts on microbial populations depend on interaction phenotypes-including viral traits spanning the adsorption rate, latent period, and burst size. The latent period is a key viral trait in lytic infections. Defined as the time from viral adsorption to viral progeny release, the latent period of bacteriophage is conventionally inferred via one-step growth curves in which the accumulation of free virus is measured over time in a population of infected cells. Developed more than 80 years ago, one-step growth curves do not account for cellular-level variability in the timing of lysis, potentially biasing inference of viral traits. Here, we use nonlinear dynamical models to understand how individual-level variation of the latent period impacts virus-host dynamics. Our modeling approach shows that inference of the latent period via one-step growth curves is systematically biased-generating estimates of shorter latent periods than the underlying population-level mean. The bias arises because variability in lysis timing at the cellular level leads to a fraction of early burst events, which are interpreted, artefactually, as an earlier mean time of viral release. We develop a computational framework to estimate latent period variability from joint measurements of host and free virus populations. Our computational framework recovers both the mean and variance of the latent period within simulated infections including realistic measurement noise. This work suggests that reframing the latent period as a distribution to account for variability in the population will improve the study of viral traits and their role in shaping microbial populations.IMPORTANCEQuantifying viral traits-including the adsorption rate, burst size, and latent period-is critical to characterize viral infection dynamics and develop predictive models of viral impacts across scales from cells to ecosystems. Here, we revisit the gold standard of viral trait estimation-the one-step growth curve-to assess the extent to which assumptions at the core of viral infection dynamics lead to ongoing and systematic biases in inferences of viral traits. We show that latent period estimates obtained via one-step growth curves systematically underestimate the mean latent period and, in turn, overestimate the rate of viral killing at population scales. By explicitly incorporating trait variability into a dynamical inference framework that leverages both virus and host time series, we provide a practical route to improve estimates of the mean and variance of viral traits across diverse virus-microbe systems.

Dietary Effects on the Gut Phageome

As knowledge of the gut microbiome has expanded our understanding of the symbiotic and dysbiotic relationships between the human host and its microbial constituents, the influence of gastrointestinal (GI) microbes both locally and beyond the intestine has become evident. Shifts in bacterial populations have now been associated with several conditions including Crohn's disease (CD), Ulcerative Colitis (UC), irritable bowel syndrome (IBS), Alzheimer's disease, Parkinson's Disease, liver diseases, obesity, metabolic syndrome, anxiety, depression, and cancers. As the bacteria in our gut thrive on the food we eat, diet plays a critical role in the functional aspects of our gut microbiome, influencing not only health but also the development of disease. While the bacterial microbiome in the context of disease is well studied, the associated gut phageome-bacteriophages living amongst and within our bacterial microbiome-is less well understood. With growing evidence that fluctuations in the phageome also correlate with dysbiosis, how diet influences this population needs to be better understood. This review surveys the current understanding of the effects of diet on the gut phageome.

Unveiling the unknown viral world in groundwater

Viruses as the prevailing biological entities are poorly understood in underground realms. Here, we establish the first metagenomic Groundwater Virome Catalogue (GWVC) comprising 280,420 viral species ( ≥ 5 kb) detected from 607 monitored wells in seven geo-environmental zones throughout China. In expanding ~10-fold the global portfolio of known groundwater viruses, we uncover over 99% novel viruses and about 95% novel viral clusters. By linking viruses to hosts from 119 prokaryotic phyla, we double the number of microbial phyla known to be virus-infected in groundwater. As keystone ultrasmall symbionts in aquifers, CPR bacteria and DPANN archaea are susceptible to virulent viruses. Certain complete CPR viruses even likely infect non-CPR bacteria, while partial CPR/DPANN viruses harbor cell-surface modification genes that assist symbiont cell adhesion to free-living microbes. This study reveals the unknown viral world and auxiliary metabolism associated with methane, nitrogen, sulfur, and phosphorus cycling in groundwater, and highlights the importance of subsurface virosphere in viral ecology.

Bacterial evolution in Biofiltration of drinking water treatment plant: Different response of phage and plasmid to varied water sources

Biofiltration in drinking water treatment (BDWT) are popular as it holds promise as an alternative to chemical treatments, yet our understanding of the key drivers and trends underlying bacterial evolution within this process remains limited. While plasmids and phages are recognized as the main vectors of horizontal gene transfer (HGT), their roles in shaping bacterial evolution in BDWT remain largely unknown. Here we leverage global metagenomic data to unravel the primary forces driving bacterial evolution in BDWT. Our results revealed that the primary vector of HGT varies depending on the type of source water (groundwater and surface water). Both plasmids and phages accelerated bacterial evolution in BDWT by enhancing genetic diversity within species, but they drove contrasting evolutionary trends in functional redundancy in different source water types. Specifically, trends towards and away from functional redundancy (indicated as gene-protein ratio) were observed in surface-water and groundwater biofilters, respectively. Virulent phages drove bacterial evolution through synergistic interactions with bacterial species capable of natural transformation and with certain natural compounds that disrupt bacterial cytoplasmic membranes. Genes relating to water purification (such as Mn(II)-oxidizing genes), microbial risks (antibiotic resistance genes), and chemical risk (polycyclic aromatic hydrocarbons) were enriched via HGT in BDWT, highlighting the necessity for heighted focus on these useful and risky objects. Overall, these discoveries enhance our understanding of bacterial evolution in BDWT and have implications for the optimization of water treatment strategies.

Opportunities and challenges in phage therapy for cardiometabolic diseases

The worldwide prevalence of cardiometabolic diseases (CMD) is increasing, and emerging evidence implicates the gut microbiota in this multifactorial disease development. Bacteriophages (phages) are viruses that selectively target a bacterial host; thus, phage therapy offers a precise means of modulating the gut microbiota, limiting collateral damage on the ecosystem. Several studies demonstrate the potential of phages in human disease, including alcoholic and steatotic liver disease. In this opinion article we discuss the potential of phage therapy as a predefined medicinal product for CMD and discuss its current challenges, including the generation of effective phage combinations, product formulation, and strict manufacturing requirements.

vAMPirus: A versatile amplicon processing and analysis program for studying viruses

Amplicon sequencing is an effective and increasingly applied method for studying viral communities in the environment. Here, we present vAMPirus, a user-friendly, comprehensive, and versatile DNA and RNA virus amplicon sequence analysis program, designed to support investigators in exploring virus amplicon sequencing data and running informed, reproducible analyses. vAMPirus intakes raw virus amplicon libraries and, by default, performs nucleotide- and amino acid-based analyses to produce results such as sequence abundance information, taxonomic classifications, phylogenies and community diversity metrics. The vAMPirus analytical framework leverages 16 different opensource tools and provides optional approaches that can increase the ratio of biological signal-to-noise and thereby reveal patterns that would have otherwise been masked. Here, we validate the vAMPirus analytical framework and illustrate its implementation as a general virus amplicon sequencing workflow by recapitulating findings from two previously published double-stranded DNA virus datasets. As a case study, we also apply the program to explore the diversity and distribution of a coral reef-associated RNA virus. vAMPirus is streamlined within Nextflow, offering straightforward scalability, standardization and communication of virus lineage-specific analyses. The vAMPirus framework is designed to be adaptable; community-driven analytical standards will continue to be incorporated as the field advances. vAMPirus supports researchers in revealing patterns of virus diversity and population dynamics in nature, while promoting study reproducibility and comparability.

Microbial diversity, genomics, and phage-host interactions of cyanobacterial harmful algal blooms

The occurrence of cyanobacterial harmful algal blooms (cyanoHABs) is related to their physical and chemical environment. However, less is known about their associated microbial interactions and processes. In this study, cyanoHABs were analyzed as a microbial ecosystem, using 1 year of 16S rRNA sequencing and 70 metagenomes collected during the bloom season from Lake Okeechobee (Florida, USA). Biogeographical patterns observed in microbial community composition and function reflected ecological zones distinct in their physical and chemical parameters that resulted in bloom "hotspots" near major lake inflows. Changes in relative abundances of taxa within multiple phyla followed increasing bloom severity. Functional pathways that correlated with increasing bloom severity encoded organic nitrogen and phosphorus utilization, storage of nutrients, exchange of genetic material, phage defense, and protection against oxidative stress, suggesting that microbial interactions may promote cyanoHAB resilience. Cyanobacterial communities were highly diverse, with picocyanobacteria ubiquitous and oftentimes most abundant, especially in the absence of blooms. The identification of novel bloom-forming cyanobacteria and genomic comparisons indicated a functionally diverse cyanobacterial community with differences in its capability to store nitrogen using cyanophycin and to defend against phage using CRISPR and restriction-modification systems. Considering blooms in the context of a microbial ecosystem and their interactions in nature, physiologies and interactions supporting the proliferation and stability of cyanoHABs are proposed, including a role for phage infection of picocyanobacteria. This study displayed the power of "-omics" to reveal important biological processes that could support the effective management and prediction of cyanoHABs.

IMPORTANCE

Cyanobacterial harmful algal blooms pose a significant threat to aquatic ecosystems and human health. Although physical and chemical conditions in aquatic systems that facilitate bloom development are well studied, there are fundamental gaps in the biological understanding of the microbial ecosystem that makes a cyanobacterial bloom. High-throughput sequencing was used to determine the drivers of cyanobacteria blooms in nature. Multiple functions and interactions important to consider in cyanobacterial bloom ecology were identified. The microbial biodiversity of blooms revealed microbial functions, genomic characteristics, and interactions between cyanobacterial populations that could be involved in bloom stability and more coherently define cyanobacteria blooms. Our results highlight the importance of considering cyanobacterial blooms as a microbial ecosystem to predict, prevent, and mitigate them.

Fecal microbiota transplantation alters gut phage communities in a clinical trial for obesity

BACKGROUND

Fecal microbiota transplantation (FMT) is a therapeutic intervention used to treat diseases associated with the gut microbiome. In the human gut microbiome, phages have been implicated in influencing human health, with successful engraftment of donor phages correlated with FMT treatment efficacy. The impact that gastrointestinal phages exert on human health has primarily been connected to their ability to modulate the bacterial communities in the gut. Nonetheless, how FMT affects recipients' phage populations, and in turn, how this influences the gut environment, is not yet fully understood. In this study, we investigated the effects of FMT on the phageome composition of participants within the Gut Bugs Trial (GBT), a double-blind, randomized, placebo-controlled trial that investigated the efficacy of FMT in treating obesity and comorbidities in adolescents. Stool samples collected from donors at the time of treatment and recipients at four time points (i.e., baseline and 6 weeks, 12 weeks, and 26 weeks post-intervention), underwent shotgun metagenomic sequencing. Phage sequences were identified and characterized in silico to examine evidence of phage engraftment and to assess the extent of FMT-induced alterations in the recipients' phageome composition.

RESULTS

Donor phages engrafted stably in recipients following FMT, composing a significant proportion of their phageome for the entire course of the study (33.8 ± 1.2% in females and 33.9 ± 3.7% in males). Phage engraftment varied between donors and donor engraftment efficacy was positively correlated with their phageome alpha diversity. FMT caused a shift in recipients' phageome toward the donors' composition and increased phageome alpha diversity and variability over time.

CONCLUSIONS

FMT significantly altered recipients' phage and, overall, microbial populations. The increase in microbial diversity and variability is consistent with a shift in microbial population dynamics. This proposes that phages play a critical role in modulating the gut environment and suggests novel approaches to understanding the efficacy of FMT in altering the recipient's microbiome.

TRIAL REGISTRATION

The Gut Bugs Trial was registered with the Australian New Zealand Clinical Trials Registry (ACTR N12615001351505). Trial protocol: the trial protocol is available at https://bmjopen.bmj.com/content/9/4/e026174 . Video Abstract.

Virus ecology and 7-year temporal dynamics across a permafrost thaw gradient

Soil microorganisms are pivotal in the global carbon cycle, but the viruses that affect them and their impact on ecosystems are less understood. In this study, we explored the diversity, dynamics, and ecology of soil viruses through 379 metagenomes collected annually from 2010 to 2017. These samples spanned the seasonally thawed active layer of a permafrost thaw gradient, which included palsa, bog, and fen habitats. We identified 5051 virus operational taxonomic units (vOTUs), doubling the known viruses for this site. These vOTUs were largely ephemeral within habitats, suggesting a turnover at the vOTU level from year to year. While the diversity varied by thaw stage and depth-related patterns were specific to each habitat, the virus communities did not significantly change over time. The abundance ratios of virus to host at the phylum level did not show consistent trends across the thaw gradient, depth, or time. To assess potential ecosystem impacts, we predicted hosts in silico and found viruses linked to microbial lineages involved in the carbon cycle, such as methanotrophy and methanogenesis. This included the identification of viruses of Candidatus Methanoflorens, a significant global methane contributor. We also detected a variety of potential auxiliary metabolic genes, including 24 carbon-degrading glycoside hydrolases, six of which are uniquely terrestrial. In conclusion, these long-term observations enhance our understanding of soil viruses in the context of climate-relevant processes and provide opportunities to explore their role in terrestrial carbon cycling.

A global atlas of soil viruses reveals unexplored biodiversity and potential biogeochemical impacts

Historically neglected by microbial ecologists, soil viruses are now thought to be critical to global biogeochemical cycles. However, our understanding of their global distribution, activities and interactions with the soil microbiome remains limited. Here we present the Global Soil Virus Atlas, a comprehensive dataset compiled from 2,953 previously sequenced soil metagenomes and composed of 616,935 uncultivated viral genomes and 38,508 unique viral operational taxonomic units. Rarefaction curves from the Global Soil Virus Atlas indicate that most soil viral diversity remains unexplored, further underscored by high spatial turnover and low rates of shared viral operational taxonomic units across samples. By examining genes associated with biogeochemical functions, we also demonstrate the viral potential to impact soil carbon and nutrient cycling. This study represents an extensive characterization of soil viral diversity and provides a foundation for developing testable hypotheses regarding the role of the virosphere in the soil microbiome and global biogeochemistry.

Influence of bacterial swimming and hydrodynamics on attachment of phages

Bacteriophages ("phages") are viruses that infect bacteria. Since they do not actively self-propel, phages rely on thermal diffusion to find target cells-but can also be advected by fluid flows, such as those generated by motile bacteria themselves in bulk fluids. How does the flow field generated by a swimming bacterium influence how it encounters phages? Here, we address this question using coupled molecular dynamics and lattice Boltzmann simulations of flagellated bacteria swimming through a bulk fluid containing uniformly-dispersed phages. We find that while swimming increases the rate at which phages attach to both the cell body and flagellar propeller, hydrodynamic interactions strongly suppress this increase at the cell body, but conversely enhance this increase at the flagellar bundle. Our results highlight the pivotal influence of hydrodynamics on the interactions between bacteria and phages, as well as other diffusible species, in microbial environments.

Phollow: Visualizing Gut Bacteriophage Transmission within Microbial Communities and Living Animals

Bacterial viruses (known as "phages") shape the ecology and evolution of microbial communities, making them promising targets for microbiome engineering. However, knowledge of phage biology is constrained because it remains difficult to study phage transmission dynamics within multi-member communities and living animal hosts. We therefore created "Phollow": a live imaging-based approach for tracking phage replication and spread in situ with single-virion resolution. Combining Phollow with optically transparent zebrafish enabled us to directly visualize phage outbreaks within the vertebrate gut. We observed that virions can be rapidly taken up by intestinal tissues, including by enteroendocrine cells, and quickly disseminate to extraintestinal sites, including the liver and brain. Moreover, antibiotics trigger waves of interbacterial transmission leading to sudden shifts in spatial organization and composition of defined gut communities. Phollow ultimately empowers multiscale investigations connecting phage transmission to transkingdom interactions that have the potential to open new avenues for viral-based microbiome therapies.

Tools and methodology to in silico phage discovery in freshwater environments

Freshwater availability is essential, and its maintenance has become an enormous challenge. Due to population growth and climate changes, freshwater sources are becoming scarce, imposing the need for strategies for its reuse. Currently, the constant discharge of waste into water bodies from human activities leads to the dissemination of pathogenic bacteria, negatively impacting water quality from the source to the infrastructure required for treatment, such as the accumulation of biofilms. Current water treatment methods cannot keep pace with bacterial evolution, which increasingly exhibits a profile of multidrug resistance to antibiotics. Furthermore, using more powerful disinfectants may affect the balance of aquatic ecosystems. Therefore, there is a need to explore sustainable ways to control the spreading of pathogenic bacteria. Bacteriophages can infect bacteria and archaea, hijacking their host machinery to favor their replication. They are widely abundant globally and provide a biological alternative to bacterial treatment with antibiotics. In contrast to common disinfectants and antibiotics, bacteriophages are highly specific, minimizing adverse effects on aquatic microbial communities and offering a lower cost-benefit ratio in production compared to antibiotics. However, due to the difficulty involving cultivating and identifying environmental bacteriophages, alternative approaches using NGS metagenomics in combination with some bioinformatic tools can help identify new bacteriophages that can be useful as an alternative treatment against resistant bacteria. In this review, we discuss advances in exploring the virome of freshwater, as well as current applications of bacteriophages in freshwater treatment, along with current challenges and future perspectives.

New avenues for potentially seeking microbial responses to climate change beneath Antarctic ice shelves

The signs of climate change are undeniable, and the impact of these changes on ecosystem function heavily depends on the response of microbes that underpin the food web. Antarctic ice shelf is a massive mass of floating ice that extends from the continent into the ocean, exerting a profound influence on global carbon cycles. Beneath Antarctic ice shelves, marine ice stores valuable genetic information, where marine microbial communities before the industrial revolution are archived. Here, in this proof-of-concept, by employing a combination of single-cell technologiesand metagenomics, we have been able to sequence frozen microbial DNA (≈300 years old) stored in the marine ice core B15 collected from the Filchnner-Ronne Ice Shelf. Metagenomic data indicated that Proteobacteria and Thaumarchaeota (e.g., Nitrosopumilus spp.), followed by Actinobacteria (e.g., Actinomarinales), were abundant. Remarkably, our data allow us to "travel to the past" and calibrate genomic and genetic evolutionary changes for ecologically relevant microbes and functions, such as Nitrosopumilus spp., preserved in the marine ice (≈300 years old) with those collected recently in seawater under an ice shelf (year 2017). The evolutionary divergence for the ammonia monooxygenase gene amoA involved in chemolithoautotrophy was about 0.88 amino acid and 2.8 nucleotide substitution rate per 100 sites in a century, while the accumulated rate of genomic SNPs was 2,467 per 1 Mb of genome and 100 years. Whether these evolutionary changes remained constant over the last 300 years or accelerated during post-industrial periods remains an open question that will be further elucidated.

IMPORTANCE

Several efforts have been undertaken to predict the response of microbes under climate change, mainly based on short-term microcosm experiments under forced conditions. A common concern is that manipulative experiments cannot properly simulate the response of microbes to climate change, which is a long-term evolutionary process. In this proof-of-concept study with a limited sample size, we demonstrate a novel approach yet to be fully explored in science for accessing genetic information from putative past marine microbes preserved under Antarctic ice shelves before the industrial revolution. This potentially allows us estimating evolutionary changes as exemplified in our study. We advocate for gathering a more comprehensive Antarctic marine ice core data sets across various periods and sites. Such a data set would enable the establishment of a robust baseline, facilitating a better assessment of the potential effects of climate change on key genetic signatures of microbes.

Warming alters life-history traits and competition in a phage community

Host-parasite interactions are highly susceptible to changes in temperature due to mismatches in species thermal responses. In nature, parasites often exist in communities, and responses to temperature are expected to vary between host-parasite pairs. Temperature change thus has consequences for both host-parasite dynamics and parasite-parasite interactions. Here, we investigate the impact of warming (37°C, 40°C, and 42°C) on parasite life-history traits and competition using the opportunistic bacterial pathogen Pseudomonas aeruginosa (host) and a panel of three genetically diverse lytic bacteriophages (parasites). We show that phages vary in their responses to temperature. While 37°C and 40°C did not have a major effect on phage infectivity, infection by two phages was restricted at 42°C. This outcome was attributed to disruption of different phage life-history traits including host attachment and replication inside hosts. Furthermore, we show that temperature mediates competition between phages by altering their competitiveness. These results highlight phage trait variation across thermal regimes with the potential to drive community dynamics. Our results have important implications for eukaryotic viromes and the design of phage cocktail therapies.IMPORTANCEMammalian hosts often elevate their body temperatures through fevers to restrict the growth of bacterial infections. However, the extent to which fever temperatures affect the communities of phages with the ability to parasitize those bacteria remains unclear. In this study, we investigate the impact of warming across a fever temperature range (37°C, 40°C, and 42°C) on phage life-history traits and competition using a bacterium (host) and bacteriophage (parasite) system. We show that phages vary in their responses to temperature due to disruption of different phage life-history traits. Furthermore, we show that temperature can alter phage competitiveness and shape phage-phage competition outcomes. These results suggest that fever temperatures have the potential to restrict phage infectivity and drive phage community dynamics. We discuss implications for the role of temperature in shaping host-parasite interactions more widely.

Profiles of phage in global hospital wastewater: Association with microbial hosts, antibiotic resistance genes, metal resistance genes, and mobile genetic elements

Hospital wastewater (HWW) is known to host taxonomically diverse microbial communities, yet limited information is available on the phages infecting these microorganisms. To fill this knowledge gap, we conducted an in-depth analysis using 377 publicly available HWW metagenomic datasets from 16 countries across 4 continents in the NCBI SRA database to elucidate phage-host dynamics and phage contributions to resistance gene transmission. We first assembled a metagenomic HWW phage catalog comprising 13,812 phage operational taxonomic units (pOTUs). The majority of these pOTUs belonged to the Caudoviricetes order, representing 75.29 % of this catalog. Based on the lifestyle of phages, we found that potentially virulent phages predominated in HWW. Specifically, 583 pOTUs have been predicted to have the capability to lyse 81 potentially pathogenic bacteria, suggesting the promising role of HWW phages as a viable alternative to antibiotics. Among all pOTUs, 1.56 % of pOTUs carry 108 subtypes of antibiotic resistance genes (ARGs), 0.96 % of pOTUs carry 76 subtypes of metal resistance genes (MRGs), and 0.96 % of pOTUs carry 22 subtypes of non-phage mobile genetic elements (MGEs). Predictions indicate that certain phages carrying ARGs, MRGs, and non-phage MGEs could infect bacteria hosts, even potential pathogens. This suggests that phages in HWW may contribute to the dissemination of resistance-associated genes in the environment. This meta-analysis provides the first global catalog of HWW phages, revealing their correlations with microbial hosts and pahge-associated ARGs, MRG, and non-phage MGEs. The insights gained from this research hold promise for advancing the applications of phages in medical and industrial contexts.

Snow viruses and their implications on red snow algal blooms

Algal blooms can give snowmelt a red color, reducing snow albedo and creating a runaway effect that accelerates snow melting. The occurrence of red snow is predicted to grow in polar and subpolar regions with increasing global temperatures. We hypothesize that these algal blooms affect virus-bacteria interactions in snow, with potential effects on snowmelt dynamics. A genomic analysis of double-stranded DNA virus communities in red and white snow from the Whistler region of British Columbia, Canada, identified 792 putative viruses infecting bacteria. The most abundant putative snow viruses displayed low genomic similarity with known viruses. We recovered the complete circular genomes of nine putative viruses, two of which were classified as temperate. Putative snow viruses encoded genes involved in energy metabolisms, such as NAD+ synthesis and salvage pathways. In model phages, these genes facilitate increased viral particle production and lysis rates. The frequency of temperate phages was positively correlated with microbial abundance in the snow samples. These results suggest the increased frequency of temperate virus-bacteria interactions as microbial densities increase during snowmelt. We propose that this virus-bacteria dynamic may facilitate the red snow algae growth stimulated by bacteria.IMPORTANCEMicrobial communities in red snow algal blooms contribute to intensifying snowmelt rates. The role of viruses in snow during this environmental shift, however, has yet to be elucidated. Here, we characterize novel viruses extracted from snow viral metagenomes and define the functional capacities of snow viruses in both white and red snow. These results are contextualized using the composition and functions observed in the bacterial communities from the same snow samples. Together, these data demonstrate the energy metabolism performed by viruses and bacteria in a snow algal bloom, as well as expand the overall knowledge of viral genomes in extreme environments.

Long-read powered viral metagenomics in the oligotrophic Sargasso Sea

Dominant microorganisms of the Sargasso Sea are key drivers of the global carbon cycle. However, associated viruses that shape microbial community structure and function are not well characterised. Here, we combined short and long read sequencing to survey Sargasso Sea phage communities in virus- and cellular fractions at viral maximum (80 m) and mesopelagic (200 m) depths. We identified 2,301 Sargasso Sea phage populations from 186 genera. Over half of the phage populations identified here lacked representation in global ocean viral metagenomes, whilst 177 of the 186 identified genera lacked representation in genomic databases of phage isolates. Viral fraction and cell-associated viral communities were decoupled, indicating viral turnover occurred across periods longer than the sampling period of three days. Inclusion of long-read data was critical for capturing the breadth of viral diversity. Phage isolates that infect the dominant bacterial taxa Prochlorococcus and Pelagibacter, usually regarded as cosmopolitan and abundant, were poorly represented.

Viruses contribute to microbial diversification in the rumen ecosystem and are associated with certain animal production traits

BACKGROUND

The rumen microbiome enables ruminants to digest otherwise indigestible feedstuffs, thereby facilitating the production of high-quality protein, albeit with suboptimal efficiency and producing methane. Despite extensive research delineating associations between the rumen microbiome and ruminant production traits, the functional roles of the pervasive and diverse rumen virome remain to be determined.

RESULTS

Leveraging a recent comprehensive rumen virome database, this study analyzes virus-microbe linkages, at both species and strain levels, across 551 rumen metagenomes, elucidating patterns of microbial and viral diversity, co-occurrence, and virus-microbe interactions. Additionally, this study assesses the potential role of rumen viruses in microbial diversification by analyzing prophages found in rumen metagenome-assembled genomes. Employing CRISPR-Cas spacer-based matching and virus-microbe co-occurrence network analysis, this study suggests that the viruses in the rumen may regulate microbes at strain and community levels through both antagonistic and mutualistic interactions. Moreover, this study establishes that the rumen virome demonstrates responsiveness to dietary shifts and associations with key animal production traits, including feed efficiency, lactation performance, weight gain, and methane emissions.

CONCLUSIONS

These findings provide a substantive framework for further investigations to unravel the functional roles of the virome in the rumen in shaping the microbiome and influencing overall animal production performance. Video Abstract.

Cross-talk and mutual shaping between the immune system and the microbiota during an oyster's life

The Pacific oyster Crassostrea gigas lives in microbe-rich marine coastal systems subjected to rapid environmental changes. It harbours a diversified and fluctuating microbiota that cohabits with immune cells expressing a diversified immune gene repertoire. In the early stages of oyster development, just after fertilization, the microbiota plays a key role in educating the immune system. Exposure to a rich microbial environment at the larval stage leads to an increase in immune competence throughout the life of the oyster, conferring a better protection against pathogenic infections at later juvenile/adult stages. This beneficial effect, which is intergenerational, is associated with epigenetic remodelling. At juvenile stages, the educated immune system participates in the control of the homeostasis. In particular, the microbiota is fine-tuned by oyster antimicrobial peptides acting through specific and synergistic effects. However, this balance is fragile, as illustrated by the Pacific Oyster Mortality Syndrome, a disease causing mass mortalities in oysters worldwide. In this disease, the weakening of oyster immune defences by OsHV-1 µVar virus induces a dysbiosis leading to fatal sepsis. This review illustrates the continuous interaction between the highly diversified oyster immune system and its dynamic microbiota throughout its life, and the importance of this cross-talk for oyster health. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Globally occurring pelagiphage infections create ribosome-deprived cells

Phages play an essential role in controlling bacterial populations. Those infecting Pelagibacterales (SAR11), the dominant bacteria in surface oceans, have been studied in silico and by cultivation attempts. However, little is known about the quantity of phage-infected cells in the environment. Using fluorescence in situ hybridization techniques, we here show pelagiphage-infected SAR11 cells across multiple global ecosystems and present evidence for tight community control of pelagiphages on the SAR11 hosts in a case study. Up to 19% of SAR11 cells were phage-infected during a phytoplankton bloom, coinciding with a ~90% reduction in SAR11 cell abundance within 5 days. Frequently, a fraction of the infected SAR11 cells were devoid of detectable ribosomes, which appear to be a yet undescribed possible stage during pelagiphage infection. We dubbed such cells zombies and propose, among other possible explanations, a mechanism in which ribosomal RNA is used as a resource for the synthesis of new phage genomes. On a global scale, we detected phage-infected SAR11 and zombie cells in the Atlantic, Pacific, and Southern Oceans. Our findings illuminate the important impact of pelagiphages on SAR11 populations and unveil the presence of ribosome-deprived zombie cells as part of the infection cycle.

Stochastic microbial dispersal drives local extinction and global diversity

Airborne dispersal of microorganisms is a ubiquitous migration mechanism, allowing otherwise independent microbial habitats to interact via biomass exchange. Here, we study the ecological implications of such advective transport using a simple spatial model for bacteria-phage interactions: the population dynamics at each habitat are described by classical Lotka-Volterra equations; however, species populations are taken as integer, that is, a discrete, positive extinction threshold exists. Spatially, species can spread from habitat to habitat by stochastic airborne dispersal. In any given habitat, the spatial biomass exchange causes incessant population density oscillations, which, as a consequence, occasionally drive species to extinction. The balance between local extinction events and dispersal-induced migration allows species to persist globally, even though diversity would be depleted by competitive exclusion, locally. The disruptive effect of biomass dispersal thus acts to increase microbial diversity, allowing system-scale coexistence of multiple species that would not coexist locally.

Taxonomic difference in marine bloom-forming phytoplanktonic species affects the dynamics of both bloom-responding prokaryotes and prokaryotic viruses

The production of dissolved organic matter during phytoplankton blooms and consumption by heterotrophic prokaryotes promote marine carbon biogeochemical cycling. Although prokaryotic viruses presumably affect this process, their dynamics during blooms are not fully understood. Here, we investigated the effects of taxonomic difference in bloom-forming phytoplankton on prokaryotes and their viruses. We analyzed the dynamics of coastal prokaryotic communities and viruses under the addition of dissolved intracellular fractions from taxonomically distinct phytoplankton, the diatom Chaetoceros sp. (CIF) and the raphidophycean alga Heterosigma akashiwo (HIF), using microcosm experiments. Ribosomal RNA gene amplicon and viral metagenomic analyses revealed that particular prokaryotes and prokaryotic viruses specifically increased in either CIF or HIF, indicating that taxonomic difference in bloom-forming phytoplankton promotes distinct dynamics of not only the prokaryotic community but also prokaryotic viruses. Furthermore, combining our microcosm experiments with publicly available environmental data mining, we identified both known and novel possible host-virus pairs. In particular, the growth of prokaryotes associating with phytoplanktonic organic matter, such as Bacteroidetes (Polaribacter and NS9 marine group), Vibrio spp., and Rhodobacteriales (Nereida and Planktomarina), was accompanied by an increase in viruses predicted to infect Bacteroidetes, Vibrio, and Rhodobacteriales, respectively. Collectively, our findings suggest that changes in bloom-forming species can be followed by an increase in a specific group of prokaryotes and their viruses and that elucidating these tripartite relationships among specific phytoplankton, prokaryotes, and prokaryotic viruses improves our understanding of coastal biogeochemical cycling in blooms.IMPORTANCEThe primary production during marine phytoplankton bloom and the consumption of the produced organic matter by heterotrophic prokaryotes significantly contribute to coastal biogeochemical cycles. While the activities of those heterotrophic prokaryotes are presumably affected by viral infection, the dynamics of their viruses during blooms are not fully understood. In this study, we experimentally demonstrated that intracellular fractions of taxonomically distinct bloom-forming phytoplankton species, the diatom Chaetoceros sp. and the raphidophycean alga Heterosigma akashiwo, promoted the growth of taxonomically different prokaryotes and prokaryotic viruses. Based on their dynamics and predicted hosts of those viruses, we succeeded in detecting already-known and novel possible host-virus pairs associating with either phytoplankton species. Altogether, we propose that the succession of bloom-forming phytoplankton would change the composition of the abundant prokaryotes, resulting in an increase in their viruses. These changes in viral composition, depending on bloom-forming species, would alter the dynamics and metabolism of prokaryotes, affecting biogeochemical cycling in blooms.

Community Structure, Drivers, and Potential Functions of Different Lifestyle Viruses in Chaohu Lake

Viruses, as the most prolific entities on Earth, constitute significant ecological groups within freshwater lakes, exerting pivotal ecological roles. In this study, we selected Chaohu Lake, a representative eutrophic freshwater lake in China, as our research site to explore the community distribution, driving mechanisms, and potential ecological functions of diverse viral communities, the intricate virus-host interaction systems, and the overarching influence of viruses on global biogeochemical cycling.

The role of rhizosphere phages in soil health

While the One Health framework has emphasized the importance of soil microbiomes for plant and human health, one of the most diverse and abundant groups-bacterial viruses, i.e. phages-has been mostly neglected. This perspective reviews the significance of phages for plant health in rhizosphere and explores their ecological and evolutionary impacts on soil ecosystems. We first summarize our current understanding of the diversity and ecological roles of phages in soil microbiomes in terms of nutrient cycling, top-down density regulation, and pathogen suppression. We then consider how phages drive bacterial evolution in soils by promoting horizontal gene transfer, encoding auxiliary metabolic genes that increase host bacterial fitness, and selecting for phage-resistant mutants with altered ecology due to trade-offs with pathogen competitiveness and virulence. Finally, we consider challenges and avenues for phage research in soil ecosystems and how to elucidate the significance of phages for microbial ecology and evolution and soil ecosystem functioning in the future. We conclude that similar to bacteria, phages likely play important roles in connecting different One Health compartments, affecting microbiome diversity and functions in soils. From the applied perspective, phages could offer novel approaches to modulate and optimize microbial and microbe-plant interactions to enhance soil health.

Hot springs viruses at Yellowstone National Park have ancient origins and are adapted to thermophilic hosts

Geothermal springs house unicellular red algae in the class Cyanidiophyceae that dominate the microbial biomass at these sites. Little is known about host-virus interactions in these environments. We analyzed the virus community associated with red algal mats in three neighboring habitats (creek, endolithic, soil) at Lemonade Creek, Yellowstone National Park (YNP), USA. We find that despite proximity, each habitat houses a unique collection of viruses, with the giant viruses, Megaviricetes, dominant in all three. The early branching phylogenetic position of genes encoded on metagenome assembled virus genomes (vMAGs) suggests that the YNP lineages are of ancient origin and not due to multiple invasions from mesophilic habitats. The existence of genomic footprints of adaptation to thermophily in the vMAGs is consistent with this idea. The Cyanidiophyceae at geothermal sites originated ca. 1.5 Bya and are therefore relevant to understanding biotic interactions on the early Earth.

Lytic/Lysogenic Transition as a Life-History Switch

The transition between lytic and lysogenic life cycles is the most important feature of the life-history of temperate viruses. To explain this transition, an optimal life-history model is offered based a discrete-time formulation of phage/bacteria population dynamics that features infection of bacteria by Poisson sampling of virions from the environment. The time step is the viral latency period. In this model, density-dependent viral absorption onto the bacterial surface produces virus/bacteria coexistence and density dependence in bacterial growth is not needed. The formula for the transition between lytic and lysogenic phases is termed the 'fitness switch'. According to the model, the virus switches from lytic to lysogenic when its population grows faster as prophage than as virions produced by lysis of the infected cells, and conversely for the switch from lysogenic to lytic. A prophage that benefits the bacterium it infects automatically incurs lower fitness upon exiting the bacterial genome, resulting in its becoming locked into the bacterial genome in what is termed here as a 'prophage lock'. The fitness switch qualitatively predicts the ecogeographic rule that environmental enrichment leads to microbialization with a concomitant increase in lysogeny, fluctuating environmental conditions promote virus-mediated horizontal gene transfer, and prophage-containing bacteria can integrate into the microbiome of a eukaryotic host forming a functionally integrated tripartite holobiont. These predictions accord more with the 'Piggyback-the-Winner' hypothesis than with the 'Kill-the-Winner' hypothesis in virus ecology.

Genome sequences of the first Autographiviridae phages infecting marine Roseobacter

The ubiquitous and abundant marine phages play critical roles in shaping the composition and function of bacterial communities, impacting biogeochemical cycling in marine ecosystems. Autographiviridae is among the most abundant and ubiquitous phage families in the ocean. However, studies on the diversity and ecology of Autographiviridae phages in marine environments are restricted to isolates that infect SAR11 bacteria and cyanobacteria. In this study, ten new roseophages that infect marine Roseobacter strains were isolated from coastal waters. These new roseophages have a genome size ranging from 38 917 to 42 634 bp and G+C content of 44.6-50 %. Comparative genomics showed that they are similar to known Autographiviridae phages regarding gene content and architecture, thus representing the first Autographiviridae roseophages. Phylogenomic analysis based on concatenated conserved genes showed that the ten roseophages form three distinct subgroups within the Autographiviridae, and sequence analysis revealed that they belong to eight new genera. Finally, viromic read-mapping showed that these new Autographiviridae phages are widely distributed in global oceans, mostly inhabiting polar and estuarine locations. This study has expanded the current understanding of the genomic diversity, evolution and ecology of Autographiviridae phages and roseophages. We suggest that Autographiviridae phages play important roles in the mortality and community structure of roseobacters, and have broad ecological applications.