The ISME Journal: Multidisciplinary Journal of Microbial Ecology is the official Journal of the International Society for Microbial Ecology, publishing high-quality, original research papers, short communications, commentary articles and reviews in the rapidly expanding and diverse discipline of microbial ecology.
The MMETSP is a significant step in recognizing that purpose-built reference databases from ecologically key biomes are essential for all domains of life. Nevertheless, it is only the beginning, and important biases remain that should be addressed. The MMETSP relies primarily on cultured organisms, and this introduces a different set of biases, most obviously, favoring organisms that are photosynthetic. Eukaryotic heterotrophs have critical ecological roles but are under-represented. Indeed, the natural diversity of eukaryotic heterotrophs is huge in general (Figure 1A), and the four most commonly recovered sequences retrieved in environmental surveys of marine samples worldwide correspond to lineages for which most members are uncultivated (e.g.,Marine Stramenopiles (MAST) and Marine Alveolates (MALV) –). These are probably heterotrophs, but we lack a solid biological definition for most of these cells and have become adroit at ignoring heterotrophs in general. Similarly, organisms from the open ocean are underrepresented. Culture-independent methods for generating transcriptomes and genomes and, in some cases, transcriptomes and genomes from single cells will be essential to moving beyond this problem. Methodologies for population – and single-cell genomics and transcriptomics are advancing rapidly ,–, transitioning from technological feats to something we should expect to work routinely. This transition holds great promise for filling the rather substantial gap in our knowledge imposed by uncultivated protists, as well as allowing us to carry out condition-specific analyses of expressed genes in difficult-to-work-with systems. The MMETSP program foreshadows this development by sequencing a small set of culture-independent samples.
Cyanobacteria coexist in the oceans with a wealth of phages that infect them. While numerous studies have investigated Synechococcus phages, much less data is available for Prochlorococcus phages. Furthermore, little is known about cyanophage composition. Here we examined the abundance and relative composition of cyanophages on six cyanobacterial hosts in samples collected during spring and summer from the Red Sea. Maximal abundances found on Synechococcus of 35,000 phages/ml are within ranges found previously whereas the 24,000 phages/ml found on Prochlorococcus are approximately 10-fold higher than previous findings. T7-like, T4-like and “unknown” phages were isolated on all hosts, including many T4-like phages on HL Prochlorococcus strains, whereas TIM5-like phages were found only on Synechococcus. Large differences in cyanophage abundance and composition were found for different hosts on the same sampling date as well as for the same host on different dates with few predictable patterns discerned. Host-range analyses showed that T7-like and TIM5-like phages were quite host-specific, whereas the breadth of hosts for T4-like phages was related to host type: those isolated on HL Prochlorococcus were considerably more host-specific than those on LL Prochlorococcus or Synechococcus. These host-related differences likely contribute to the complexity of host-phage interactions in the oceans.
Multiple studies have explored microbial shifts in diseased or stressed corals, however little is known about bacteriophage interactions with microbes in this context. This study characterized microbial 16S rRNA amplicons and phage metagenomes associated with Montastraea annularis corals during a concurrent white plague disease outbreak and bleaching event. Phage consortia differed between bleached and diseased tissues. Phages in the family Inoviridae were elevated in diseased or healthy tissues compared to bleached portions of diseased tissues. Microbial communities also differed between diseased and bleached corals. Bacteria in the orders Rhodobacterales and Campylobacterales were increased while Kiloniellales was decreased in diseased compared to other tissues. A network of phage-bacteria interactions was constructed of all phage strains and 11 bacterial genera that differed across health states. Phage-bacteria interactions varied in specificity: phages interacted with 1-8 bacterial hosts while bacteria interacted with up to 59 phages. Six phages were identified that interacted exclusively with Rhodobacterales and Camplyobacterales. These results suggest that phages have a role in controlling stress-associated bacteria, and that networks can be utilized to select potential phages for mitigating detrimental bacterial growth in phage therapy applications.
Mya Breitbart's insight:
Very interesting --- links between coral health, bacterial communities, and phages! Also one of the first studies to find Inoviruses in the oceans that I'm aware of.
In 2003, Acanthamoeba polyphaga mimivirus (APMV) was first described and began to impact researchers around the world, due to its structural and genetic complexity. This virus founded the family Mimiviridae. In recent years, several new giant viruses have been isolated from different environments and specimens. Giant virus research is in its initial phase and information that may arise in the coming years may change current conceptions of life, diversity and evolution. Thus, this review aims to condense the studies conducted so far about the features and peculiarities of APMV, from its discovery to its clinical relevance.
A number of bivalve species worldwide, including the Pacific oyster,Crassostrea gigas, have been affected by mass mortality events associated with herpesviruses and resulting in significant losses. A particular herpesvirus was purified from naturally infected larval Pacific oysters and its genome was entirely sequenced. This virus has been classified asOstreid herpesvirus 1 (OsHV-1) within the Malacoherpesviridae family. Since 2008, mass mortality outbreaks among C. gigas in Europe have been related to the detection of a variant of OsHV-1 called μVar.
Additional data is necessary to better describe mortality events in relation with environmental parameter fluctuations and OsHV-1 detection. For this purpose, a single batch of Pacific oyster spat was deployed in 4 different locations in the Marennes-Oleron area (France) including a pond (“claire”), a shellfish nursery and two locations in the field. Mortality rates were recorded based on regular observation and samples were collected to search and quantify OsHV-1 DNA by real time PCR. Although similar massive mortality rates were reported at 4 sites, mortality was detected earlier in the pond and in the nursery than at both field sites. This difference may be related to earlier increases of water temperature. Mass mortality was observed among oysters a few days after increases of the number of PCR positive oysters and viral DNA amounts were recorded. A initial increment in the number of PCR positive oysters was reported at both field sites during the survey in absence of significant mortality. During this period the water temperature was below 16°C.
Ed Rybicki's insight:
Clever idea: trawling for viruses with bait organisms in an aquaculture setting.
Nucleocytoplasmic large DNA viruses (NCLDVs) are eukaryotic viruses with large genomes (100 kb–2.5 Mb), which include giant Mimivirus, Megavirus and Pandoravirus. NCLDVs are known to infect animals, protists and phytoplankton but were never described as pathogens of land plants. Here, we show that the bryophyte Physcomitrella patens and the lycophyte Selaginella moellendorffii have open reading frames (ORFs) with high phylogenetic affinities to NCLDV homologues. The P. patens genes are clustered in DNA stretches (up to 13 kb) containing up to 16 NCLDV-like ORFs. Molecular evolution analysis suggests that the NCLDV-like regions were acquired by horizontal gene transfer from distinct but closely related viruses that possibly define a new family of NCLDVs. Transcriptomics and DNA methylation data indicate that the NCLDV-like regions are transcriptionally inactive and are highly cytosine methylated through a mechanism not relying on small RNAs. Altogether, our data show that members of NCLDV have infected land plants.
Cafeteria roenbergensis virus (CroV) is a giant virus of the Mimiviridae family that infects the marine phagotrophic flagellate C. roenbergensis. CroV possesses a DNA genome of ~730 kilobase pairs that is predicted to encode 544 proteins. We analyzed the protein composition of purified CroV particles by liquid chromatography–tandem mass spectrometry (LC–MS/MS) and identified 141 virion-associated CroV proteins and 60 host proteins. Data are available via ProteomeXchange with identifier PXD000993. Predicted functions could be assigned to 36% of the virion proteins, which include structural proteins as well as enzymes for transcription, DNA repair, redox reactions and protein modification. Homologs of 36 CroV virion proteins have previously been found in the virion of Acanthamoeba polyphaga mimivirus. The overlapping virion proteome of CroV and Mimivirus reveals a set of conserved virion protein functions that were presumably present in the last common ancestor of the Mimiviridae.
Ed Rybicki's insight:
I love this stuff: I am going to work VERY hard at getting money to carry on with our modest project.
Liquid water has been known to occur beneath the Antarctic ice sheet for more than 40 years, but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale. Here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial Antarctic lake. Subglacial Lake Whillans (SLW) lies beneath approximately 800 m of ice on the lower portion of the Whillans Ice Stream (WIS) in West Antarctica and is part of an extensive and evolving subglacial drainage network. The water column of SLW contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component. Heterotrophic and autotrophic production data together with small subunit ribosomal RNA gene sequencing and biogeochemical data indicate that SLW is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea. Our results confirm that aquatic environments beneath the Antarctic ice sheet support viable microbial ecosystems, corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes that can mobilize elements from the lithosphere and influence Southern Ocean geochemical and biological systems.
Microbes drive myriad ecosystem processes, and their viruses modulate microbial-driven processes through mortality, horizontal gene transfer, and metabolic reprogramming by viral-encoded auxiliary metabolic genes (AMGs). However, our knowledge of viral roles in the oceans is primarily limited to surface waters. Here we assess the depth distribution of protein clusters (PCs) in the first large-scale quantitative viral metagenomic data set that spans much of the pelagic depth continuum (the Pacific Ocean Virome; POV). This established ‘core’ (180 PCs; one-third new to science) and ‘flexible’ (423K PCs) community gene sets, including niche-defining genes in the latter (385 and 170 PCs are exclusive and core to the photic and aphotic zones, respectively). Taxonomic annotation suggested that tailed phages are ubiquitous, but not abundant (<5% of PCs) and revealed depth-related taxonomic patterns. Functional annotation, coupled with extensive analyses to document non-viral DNA contamination, uncovered 32 new AMGs (9 core, 20 photic and 3 aphotic) that introduce ways in which viruses manipulate infected host metabolism, and parallel depth-stratified host adaptations (for example, photic zone genes for iron–sulphur cluster modulation for phage production, and aphotic zone genes for high-pressure deep-sea survival). Finally, significant vertical flux of photic zone viruses to the deep sea was detected, which is critical for interpreting depth-related patterns in nature. Beyond the ecological advances outlined here, this catalog of viral core, flexible and niche-defining genes provides a resource for future investigation into the organization, function and evolution of microbial molecular networks to mechanistically understand and model viral roles in the biosphere.
Mya Breitbart's insight:
Very nice comparison of auxiliary metabolic genes throughout the water column - and interesting that they found photosynthetic AMGs in the deep ocean showing vertical flux of viral particles!
Metagenomics, or sequencing of the genetic material from a complete microbial community, is a promising tool to discover novel microbes and viruses. Viral metagenomes typically contain many unknown sequences. Here we describe the discovery of a previously unidentified bacteriophage present in the majority of published human faecal metagenomes, which we refer to as crAssphage. Its ~97 kbp genome is six times more abundant in publicly available metagenomes than all other known phages together; it comprises up to 90% and 22% of all reads in virus-like particle (VLP)-derived metagenomes and total community metagenomes, respectively; and it totals 1.68% of all human faecal metagenomic sequencing reads in the public databases. The majority of crAssphage-encoded proteins match no known sequences in the database, which is why it was not detected before. Using a new co-occurrence profiling approach, we predict a Bacteroides host for this phage, consistent with Bacteroides-related protein homologues and a unique carbohydrate-binding domain encoded in the phage genome.
Mya Breitbart's insight:
Not quite about Aquatic Viruses, but too cool not to share. PS - love the name!
Microbes and their viruses drive myriad processes across ecosystems ranging from oceans and soils to bioreactors and humans. Despite this importance, microbial diversity is only now being mapped at scales relevant to nature, while the viral diversity associated with any particular host remains little researched. Here we quantify host-associated viral diversity using viral-tagged metagenomics, which links viruses to specific host cells for high-throughput screening and sequencing. In a single experiment, we screened 107 Pacific Ocean viruses against a single strain of Synechococcus and found that naturally occurring cyanophage genome sequence space is statistically clustered into discrete populations. These population-based, host-linked viral ecological data suggest that, for this single host and seawater sample alone, there are at least 26 double-stranded DNA viral populations with estimated relative abundances ranging from 0.06 to 18.2%. These populations include previously cultivated cyanophage and new viral types missed by decades of isolate-based studies. Nucleotide identities of homologous genes mostly varied by less than 1% within populations, even in hypervariable genome regions, and by 42-71% between populations, which provides benchmarks for viral metagenomics and genome-based viral species definitions. Together these findings showcase a new approach to viral ecology that quantitatively links objectively defined environmental viral populations, and their genomes, to their hosts.
Mya Breitbart's insight:
Very cool method for linking marine phage with their hosts...
Viruses (including bacteriophages) are the most abundant biological entities on the planet. As such, they are thought to have a major impact on all aspects of microbial community structure and function. Despite this critical role in ecosystem processes, the study of virus/phage diversity has lagged far behind parallel studies of the bacterial and eukaryotic kingdoms, largely due to the absence of any universal phylogenetic marker. Here we review the development and use of signature genes to investigate viral diversity, as a viable strategy for data sets of specific virus groups. Genes that have been used include those encoding structural proteins, such as portal protein, major capsid protein, and tail sheath protein, auxiliary metabolism genes, such as psbA, psbB, and phoH, and several polymerase genes. These marker genes have been used in combination with PCR-based fingerprinting and/or sequencing strategies to investigate spatial, temporal, and seasonal variations and diversity in a wide range of habitats.
Mya Breitbart's insight:
Since there is no universal gene found in all viruses - these "signature genes" provide a good method for surveying subsets of viral diversity
Viruses are known as the most abundant and genetically diverse life forms on the planet, but there is still a lack of information on many of the various types that make up this group, including the phylogenetic relationships between them. Single-stranded DNA (ssDNA) viruses have previously been divided up into seven known families and are known to infect many plants and animals, and have small genomes (between 1.4 and 8.5 kb). Of these seven families, there are currently two groups of bacteriophages (Inoviridae andMicroviridae) and five that infect eukaryotes (Nanoviridae and Geminiviridae which infect plants; and Circoviridae, Parvoviridae and Anelloviridae which infect animals). The genomes of these ssDNA viruses are able to encode as few as two genes; a capsid and a replication initiator.
Marine sediments cover two-thirds of our planet and harbor huge numbers of living prokaryotes. Long-term survival of indigenous microorganisms within the deep subsurface is still enigmatic, as sources of organic carbon are vanishingly small. To better understand controlling factors of microbial life, we have analyzed viral abundance within a comprehensive set of globally distributed subsurface sediments. Phages were detected by electron microscopy in deep (320 m below seafloor), ancient (~14 Ma old) and the most oligotrophic subsurface sediments of the world’s oceans (South Pacific Gyre (SPG)). The numbers of viruses (104–109 cm−3, counted by epifluorescence microscopy) generally decreased with sediment depth, but always exceeded the total cell counts. The enormous numbers of viruses indicate their impact as a controlling factor for prokaryotic mortality in the marine deep biosphere. The virus-to-cell ratios increased in deeper and more oligotrophic layers, exhibiting values of up to 225 in the deep subsurface of the SPG. High numbers of phages might be due to absorption onto the sediment matrix and a diminished degradation by exoenzymes. However, even in the oldest sediments, microbial communities are capable of maintaining viral populations, indicating an ongoing viral production and thus, viruses provide an independent indicator for microbial life in the marine deep biosphere.
Continental shelves and the waters overlying them support numerous industries as diverse as tourism and recreation, energy extraction, fisheries, transportation, and applications of marine bio-molecules (e.g., agribusiness, food processing, pharmaceuticals). Although these shelf ecosystems exhibit impacts of climate change and increased human use of resources (Halpern et al., 2012; IPCC, 2013, 2014; Melillo et al., 2014), there are currently no standardized metrics for assessing changes in ecological function in the coastal ocean. Here, we argue that it is possible to monitor vital signs of ecosystem function by focusing on the lowest levels of the ocean food web. Establishment of biodiversity, biomass, and primary productivity baselines and continuous evaluation of changes in biological resources in these economically and ecologically valuable regions requires an internationally coordinated monitoring effort that fully integrates natural, social, and economic sciences to jointly identify problems and design solutions. Such an ocean observing network is needed to protect the livelihoods of coastal communities in the context of the goals of the Future Earth program (Mooney et al., 2013) and of the Intergovernmental Platform on Biodiversity and Ecosystem Services (http://www.ipbes.net). The tools needed to initiate these assessments are available today.
In marine environments, virus-mediated lysis of host cells leads to the release of cellular carbon and nutrients and is hypothesized to be a major driver of carbon recycling on a global scale. However, efforts to characterize the effects of viruses on nutrient cycles have overlooked the geochemical potential of the virus particles themselves, particularly with respect to their phosphorus content. In this Analysis article, we use a biophysical scaling model of intact virus particles that has been validated using sequence and structural information to quantify differences in the elemental stoichiometry of marine viruses compared with their microbial hosts. By extrapolating particle-scale estimates to the ecosystem scale, we propose that, under certain circumstances, marine virus populations could make an important contribution to the reservoir and cycling of oceanic phosphorus.
The genome of CroV has a size of 744kb and encodes for 544 predicted genes. CroV derived its name from its host, a unicellular marine zooplankton Cafeteria roenbergensis (Cro) that is the major microbial grazer in the ocean. By controlling Cro's population, CroV has a great impact on the marine ecological system. CroV is covered by a protein shell (capsid) comprised of major capsid proteins (MCP) and minor capsid proteins (mCP). The capsid not only protects the genetic material of the virus, but also helps in host-virus recognition, which is the critical initial step for viral infection. This research focuses on obtaining large amount homogenous CroV MCP for future structural studies that will facilitate the understanding of the roles of MCP in the viral life cycle.