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Viruses are abundant in the ocean and influence both the composition of marine communities and biogeochemical cycles. Despite their high abundance, production rates of distinct virus taxa in the environment are largely unknown. Here, we investigated production dynamics of T4-like cyanophages and compared them to those of the total dsDNA virioplankton community in two adjacent eddies of opposite polarity in the North Pacific Subtropical Gyre. Virioplankton production rateswere 3-fold higher in the cyclonic than in the anticyclonic eddy, potentially due to higher metabolic activity of their bacterial hosts in the cyclone, and had similar virus production rates during the day and night in the cyclone. In contrast, T4-like cyanophages had similar production rates in the two eddies but showed approximately 4-fold higher production rates at night than during the day, potentially due to a combination of greater infection, increased burst size and more cyanophages completing their infection cycle at night. These findings suggest that virioplankton community production is affected more by spatially differentiated environmental conditions while T4-like cyanophage production is more affected over the diel cycle. Differences in production for the T4-like cyanophages relative to the virioplankton community indicate that spatial variability at the mesoscale differentially impact distinct components of the virioplankton. [ABSTRACT FROM AUTHOR]

Variations of picoplankton groups were investigated over a one-month period in Daya Bay and Sanya Bay, in the northern South China Sea. The two coastal regions exhibited different variation patterns in physicochemical parameters. Moreover, the diel variations of picoplankton groups were different between the two bays. The abundance of the picoplankton in Sanya Bay displayed a pronounced diel variation, while it was not significant in Daya Bay. In addition, some similar patterns of picoplankton abundance were discovered. In the two bays, virioplankton exhibited the smallest fluctuation range, whereas picocyanobacteria fluctuated most markedly. The fluctuation range of picoplankton groups was larger in spring tide than in neap tide, especially in Sanya Bay. Random forest model analysis demonstrated that the variation of picoplankton groups was attributed to physical and chemical factors in Sanya Bay and Daya Bay, respectively. Therefore, our findings suggest that virioplankton abundance can persist more stably in response to changing environmental conditions compared to bacterioplankton and picophytoplankton. [ABSTRACT FROM AUTHOR]

Viruses are abundant in the ocean and influence both the composition of marine communities and biogeochemical cycles. Despite their high abundance, production rates of distinct virus taxa in the environment are largely unknown. Here, we investigated production dynamics of T4-like cyanophages and compared them to those of the total dsDNA virioplankton community in two adjacent eddies of opposite polarity in the North Pacific Subtropical Gyre. Virioplankton production rates were 3-fold higher in the cyclonic than in the anticyclonic eddy, potentially due to higher metabolic activity of their bacterial hosts in the cyclone, and had similar virus production rates during the day and night in the cyclone. In contrast, T4-like cyanophages had similar production rates in the two eddies but showed approximately 4-fold higher production rates at night than during the day, potentially due to a combination of greater infection, increased burst size and more cyanophages completing their infection cycle at night. These findings suggest that virioplankton community production is affected more by spatially differentiated environmental conditions while T4-like cyanophage production is more affected over the diel cycle. Differences in production for the T4-like cyanophages relative to the virioplankton community indicate that spatial variability at the mesoscale differentially impact distinct components of the virioplankton.

New data have been obtained on the distribution of prokaryotic plankton and pelagic viruses in the Fram Strait (the Greenland Sea) during the polar night (late November). Three main types of water masses were present in the study area: surface polar, Atlantic, and transformed Atlantic. The content of mineral biogenic elements increased with depth. The concentration of chlorophyll a had low values (0.07–0.13 mg/m3). The abundance and biomass of prokaryotes varied from 286 000 to 675 000 cells/mL and from 2.7 to 11.7 mg C/m3, respectively. The composition of prokaryotic plankton was dominated by single small cells (more than 97% of the abundance and more than 68% of the biomass). The average cell volume was 0.034–0.096 μm3. The number of viruses varied from 724 000 to 3 920 000 particles/mL, and the biomass varied from 0.040 to 0.216 μg C/m3. Against the background of local maxima in the abundance of prokaryotic plankton in the 0–25 m layer, the highest concentrations of viruses were noted in the surface layer. In the latitudinal distribution (from south to north), an increase in the number of viruses and prokaryotes was revealed. A close relationship between their abundance and biomass with hydrological parameters and phosphate content was established; the role of certain water masses in the vertical distribution of microbes was insignificant. The relatively high abundance of viruses and prokaryotes indicated their significant activity during the polar night. [ABSTRACT FROM AUTHOR]

Simple Summary: Plankton are a key component of Arctic marine ecosystems, connecting all trophic levels and being involved in organic matter recycling. Our main purpose was to reveal differences in plankton characteristics in two Arctic sites that were strongly affected by the inflow of warm Atlantic waters during the period of polar night. We detected similar bacterial abundances in both regions, while other plankton parameters were significantly different. Temperature, salinity, and sampling depth shaped the plankton communities. Phytoplankton biomass also had a marked influence on microbial abundance and zooplankton assemblages. Changes in the proportions of boreal taxa suggested the Atlantification of pelagic communities, a phenomenon reported in the Arctic due to global warming. We studied the spatial patterns of the planktonic ecosystems at two Arctic sites strongly affected by Atlantic Inflow (FS, the Fram Strait; and BS, the Barents Sea). A high degree of similarity in the bacterial abundance (mean: 3.1 × 105 cells mL−1 in FS vs. 3.5 × 105 cells mL−1 in BS) was found, while other plankton characteristics were different. Bacterial biomass reached a maximum in BS (3.2–7.9 mg C m−3), while viral abundances tended to be higher in FS (2.0–5.7 × 106 particles mL−1). Larger bacterial cells were found in BS, suggesting the presence of different bacterial populations at both locations. The virus-to-bacteria ratio was significantly higher in FS than in BS (13.5 vs. 4.7). Chlorophyll a concentration was extremely low (<0.25 mg m−3). The highest zooplankton abundance was in the surface layer (919 individuals m−3 in FS vs. 602 ind. m−3 in BS). Zooplankton biomass strongly varied (1–39 mg C m−3), with the maximum in BS. High proportions of boreal taxa in the total zooplankton abundance indicate the Atlantification of pelagic ecosystems in the Arctic. Plankton indicators are correlated with temperature, salinity, and sampling depth. Strong intercorrelations were found between major plankton groups, suggesting tight links in the studied plankton ecosystems. [ABSTRACT FROM AUTHOR]

Virioplankton and picoplankton are the most abundant marine biological entities on earth and mediate biogeochemical cycles in the Southern Ocean. However, understanding of their distribution and relationships with environmental factors is lacking. Here, we report on their distribution and relationships with environmental factors at 48 stations from 112.5° to 150°W and 67° to 75.5°S in the Amundsen Sea of West Antarctica. The epipelagic stations were grouped into four clusters based on the virio- and picoplankton composition and abundance. Clusters three and four, which were associated with the ice-edge blooms in the coastal and Amundsen Sea Polynya (ASP) areas, had high abundances of autotrophic picoeukaryotes; this resulted in subsequent high abundances of heterotrophic prokaryotes and viruses. Cluster two stations were in open oceanic areas, where the abundances of autotrophic and heterotrophic picoplankton were low. Cluster one stations were located between the areas of blooms and the oceanic areas, which had a low abundance of heterotrophic prokaryotes and picoeukaryotes and a high abundance of virioplankton. The abundance of viruses was significantly correlated with the abundances of autotrophic picoeukaryotes and Chl-a concentration in oceanic areas, although this reflected a time-lag with autotrophic picoeukaryote and heterotrophic prokaryotes abundances in ice-edge bloom areas. The upwelling of Circumpolar Deep Water (CDW) might have induced the high abundance of autotrophic picoeukaryotes in the epipelagic zone, and the sinking particulate organic carbon (POC) might have induced the high abundance of heterotrophic prokaryotes and virioplankton in the meso- and bathypelagic zones. This study shows that the summer distribution of virio- and picoplankton in the Amundsen Sea of West Antarctica was mainly controlled by upwelling of the CDW and the timing of ice-edge blooms. [ABSTRACT FROM AUTHOR]

Simple Summary: Microbial plankton represent a pivotal component of aquatic ecosystems worldwide. Despite their importance in pelagic ecosystems, microbial assemblages are less studied, in many Arctic regions. The study was concerned with the abundance of marine bacteria and viruses, in relation to a set of environmental variables, after the main productive season. We found a mosaic horizontal distribution of the microbial plankton, while the number of bacteria and viruses decreased with depth. Nutrients and zooplankton carbon were significant drivers of microbial abundance. Bacterioplankton abundance was positively correlated with counts of viruses, indicating close relations between these groups of microbes. Comparisons with previous studies revealed strong seasonal variations in the total abundance of marine bacteria, with the maximum values being in the summer and spring periods, while virioplankton counts were comparable in the autumn and spring–summer seasons. Our study is the first report regarding microbial plankton in the northeastern Barents Sea, in the autumn period, and provides baseline information, expanding current knowledge on the structure of pelagic Arctic ecosystems. In the marine environment, bacteria and viruses play a significant role in carbon fluxes, remineralization processes, and the infection of various organisms. We performed a survey in the northeastern Barents Sea, a region adjacent to the Arctic Ocean, to investigate spatial patterns of microbial plankton, after the main productive period, in October 2020. Two main water masses occurred in the study region—colder Arctic Water and warmer Barents Sea Water, representing transformed Atlantic Water. Multivariate analyses detected patchiness in the horizontal distribution of bacteria and viruses, and their abundances showed no clear association with the water masses. There was an obvious vertical pattern in microbial concentration, with the highest estimates in the upper layers. Surface viral and bacterial abundance varied in a wide range (2.20 × 105–10.7 × 105 cells·mL−1 and 0.86 × 106–14.98 × 106 particles·mL−1, respectively) and were correlated with each other. Bacterioplankton was dominated by small-sized cells (<2 μm, 0.04–0.06 µm3), and the average volume of bacterial cells tended to increase toward the seafloor. The ratio of viral to bacterial abundance (VBR) was 11 ± 1 and did not differ between water masses and depth layers. VBR were higher, compared to summer values, suggesting a strong impact of viruses on bacterioplankton, after the main productive season. Redundancy and correlation analyses showed that inorganic nutrients (nitrate and phosphate) and organic carbon from zooplankton were most responsible for the total variability in the microbial parameters. Water temperature and salinity, also, had a measurable impact, but their influence was lower. Bacterial abundance was lower than in other seasons and regions of the Barents Sea, while viral abundance was comparable, suggesting a stronger viral impact on Arctic marine bacteria in the autumn season. [ABSTRACT FROM AUTHOR]

The first study on the dynamics of virioplankton abundance (VA) in the coastal waters of the Moscow River in the autumn–winter period at stations differing in the level of anthropogenic impact has been performed. The VA in the waters of the more polluted Dzerzhinsky st. (with a mean of 235.6 ± 71.5 × 106 particles/mL, varying from 167.79 to 397.39 × 106 particles/mL) was higher than in the waters of the less polluted Tushino st. (with a mean value of 129.0 ± 39.6 × 106 particles/mL, varying from 61.01 to 186.85 × 106 particles/mL) throughout the study. Positive correlation was observed (R = 0.6, p < 0.01) between the abundances of virio- and bacterioplankton in the waters of the Dzerzhinsky st. We assume that a significant proportion of the virioplankton of the coastal waters o of the Moscow River is represented by bacteriophages. Three quarters of the differences in the VA dynamics were significantly positively correlated with the content of ammonium and phosphates in the waters at the Dzerzhinsky st. Apparently, an increase in the nutrient load is the main factor responsible for the high VA in the waters of the Moscow River in the autumn–winter period. [ABSTRACT FROM AUTHOR]

We studied the spatial patterns of the planktonic ecosystems at two Arctic sites strongly affected by Atlantic Inflow (FS, the Fram Strait; and BS, the Barents Sea). A high degree of similarity in the bacterial abundance (mean: 3.1 × 105 cells mL−1 in FS vs. 3.5 × 105 cells mL−1 in BS) was found, while other plankton characteristics were different. Bacterial biomass reached a maximum in BS (3.2–7.9 mg C m−3), while viral abundances tended to be higher in FS (2.0–5.7 × 106 particles mL−1). Larger bacterial cells were found in BS, suggesting the presence of different bacterial populations at both locations. The virus-to-bacteria ratio was significantly higher in FS than in BS (13.5 vs. 4.7). Chlorophyll a concentration was extremely low (−3). The highest zooplankton abundance was in the surface layer (919 individuals m−3 in FS vs. 602 ind. m−3 in BS). Zooplankton biomass strongly varied (1–39 mg C m−3), with the maximum in BS. High proportions of boreal taxa in the total zooplankton abundance indicate the Atlantification of pelagic ecosystems in the Arctic. Plankton indicators are correlated with temperature, salinity, and sampling depth. Strong intercorrelations were found between major plankton groups, suggesting tight links in the studied plankton ecosystems.

Abstract The shallow Caroline Seamount is located in the tropical western Pacific Ocean. Its summit is 57 m below the surface and penetrates the euphotic zone. Therefore, it is ideal for the study of the influence of seamount on plankton distribution. Here, virioplankton abundance and distribution were investigated by flow cytometry (FCM) in the Caroline Seamount in August and September 2017. The total abundance of virus‐like particles (VLP) was in the range of 0.64 × 106–18.77 × 106 particles/ml and the average was 5.37 ± 3.75 × 106 particles/ml. Three to four distinct viral subclusters with similar side scatter but different green fluorescence intensities were identified. Above the deep chlorophyll maximum (DCM), two medium fluorescence virus (MFV) subclusters were discriminated. Between the DCM and the deeper layers, only one MFV subcluster was resolved. In general, low fluorescence viruses (LFV) comprised the most abundant subclusters. In the 75–150 m water column, however, the MFV abundance was higher than the LFV abundance. High fluorescence viruses (HFV) constituted the least abundant subcluster throughout the entire water column. Virioplankton abundance was significantly enhanced at the seamount stations. Environmental factors including water temperature and nitrate concentration were the most correlated with the variation in virioplankton abundance at the seamount stations. Interactions between shallow seamounts and local currents can support large virus standing stocks, causing a so‐called indirect “seamount effect” on the virioplankton.

Inspired by recent discoveries of the prevalence of large viruses in the environment, we reassessed the longstanding approach of filtering water through small-pore-size filters to separate viruses from cells before metagenomic analysis. We collected samples from three sites in Hamilton Harbour, an embayment of Lake Ontario, and studied 6 data sets derived from <0.45-μm-and>0.45-μm-size fractions to compare the diversity of viruses in these fractions. At the level of virus order/family, we observed highly diverse and distinct virus communities in the >0.45-μm-size fractions, whereas the <0.45-μm-size fractions were composed primarily of Caudovirales. The relative abundances of Caudovirales for which hosts could be inferred varied widely between size fractions, with higher relative abundances of cyanophages in the >0.45-μm-size fractions, potentially indicating replication within cells during ongoing infections. Many viruses of eukaryotes, such as Mimiviridae, Phycodnaviridae, Iridoviridae, and Poxviridae, were detected exclusively in the oftendisregarded >0.45-μm-size fractions. In addition to observing unique virus communities associated with each size fraction from every site we examined, we detected viruses common to both fractions, suggesting that these are candidates for further exploration because they could be the product of ongoing or recent lytic events. Most importantly, our observations indicate that analysis of either fraction alone provides only a partial perspective of double-stranded DNA (dsDNA) viruses in the environment, highlighting the need for more comprehensive approaches for analyzing virus communities inferred from metagenomic sequencing. [ABSTRACT FROM AUTHOR]

In the marine environment, bacteria and viruses play a significant role in carbon fluxes, remineralization processes, and the infection of various organisms. We performed a survey in the northeastern Barents Sea, a region adjacent to the Arctic Ocean, to investigate spatial patterns of microbial plankton, after the main productive period, in October 2020. Two main water masses occurred in the study region—colder Arctic Water and warmer Barents Sea Water, representing transformed Atlantic Water. Multivariate analyses detected patchiness in the horizontal distribution of bacteria and viruses, and their abundances showed no clear association with the water masses. There was an obvious vertical pattern in microbial concentration, with the highest estimates in the upper layers. Surface viral and bacterial abundance varied in a wide range (2.20 × 105–10.7 × 105 cells·mL−1 and 0.86 × 106–14.98 × 106 particles·mL−1, respectively) and were correlated with each other. Bacterioplankton was dominated by small-sized cells (3), and the average volume of bacterial cells tended to increase toward the seafloor. The ratio of viral to bacterial abundance (VBR) was 11 ± 1 and did not differ between water masses and depth layers. VBR were higher, compared to summer values, suggesting a strong impact of viruses on bacterioplankton, after the main productive season. Redundancy and correlation analyses showed that inorganic nutrients (nitrate and phosphate) and organic carbon from zooplankton were most responsible for the total variability in the microbial parameters. Water temperature and salinity, also, had a measurable impact, but their influence was lower. Bacterial abundance was lower than in other seasons and regions of the Barents Sea, while viral abundance was comparable, suggesting a stronger viral impact on Arctic marine bacteria in the autumn season.

ABSTRACT Viruses are ubiquitous and abundant in the oceans, and viral metagenomes (viromes) have been investigated extensively via several large-scale ocean sequencing projects. However, there have not been any systematic viromic studies in estuaries. Here, we investigated the viromes of the Delaware Bay and Chesapeake Bay, two Mid-Atlantic estuaries. Deep sequencing generated a total of 48,190 assembled viral sequences (>5 kb) and 26,487 viral populations (9,204 virus clusters and 17,845 singletons), including 319 circular viral contigs between 7.5 kb and 161.8 kb. Unknown viruses represented the vast majority of the dominant populations, while the composition of known viruses, such as pelagiphage and cyanophage, appeared to be relatively consistent across a wide range of salinity gradients and in different seasons. A difference between estuarine and ocean viromes was reflected by the proportions of Myoviridae, Podoviridae, Siphoviridae, Phycodnaviridae, and a few well-studied virus representatives. The difference in viral community between the Delaware Bay and Chesapeake Bay is significantly more pronounced than the difference caused by temperature or salinity, indicating strong local profiles caused by the unique ecology of each estuary. Interestingly, a viral contig similar to phages infecting Acinetobacter baumannii (“Iraqibacter”) was found to be highly abundant in the Delaware Bay but not in the Chesapeake Bay, the source of which is yet to be identified. Highly abundant viruses in both estuaries have close hits to viral sequences derived from the marine single-cell genomes or long-read single-molecule sequencing, suggesting that important viruses are still waiting to be discovered in the estuarine environment. IMPORTANCE This is the first systematic study about spatial and temporal variation of virioplankton communities in estuaries using deep metagenomics sequencing. It is among the highest-quality viromic data sets to date, showing remarkably consistent sequencing depth and quality across samples. Our results indicate that there exists a large pool of abundant and diverse viruses in estuaries that have not yet been cultivated, their genomes only available thanks to single-cell genomics or single-molecule sequencing, demonstrating the importance of these methods for viral discovery. The spatiotemporal pattern of these abundant uncultivated viruses is more variable than that of cultured viruses. Despite strong environmental gradients, season and location had surprisingly little impact on the viral community within an estuary, but we saw a significant distinction between the two estuaries and also between estuarine and open ocean viromes.

The distribution of heterotrophic bacteria, viruses, and heterotrophic nanoflagellates was studied in the shelf waters of the East Siberian Sea along the meridional transect from the Kolyma River delta in September. The production of heterotrophic bacteria and their mortality as a result of protozoan grazing and lysis of viruses were also determined. The patterns of the spatial distribution of microorganisms and viruses varied: the number of bacterioplankton decreased with increasing distance from the Kolyma delta, while, on the contrary, its size and biomass increased to the shelf areas with negative water temperatures. The highest abundance and biomass of virioplankton were recorded at the extreme southern and northern stations of the transect and the abundance and biomass of heterotrophic nanoflagellates increased from the south to the north. The studied shelf waters were characterized by a high concentration of fine-textured detrital particles, and, as a consequence, a relatively large number of viruses attached to detritus. The mortality of heterotrophic bacterioplankton accounted for most of its daily production. Protozoan grazing was the main cause of bacterial mortality that significantly exceeded their mortality due to viral lysis. [ABSTRACT FROM AUTHOR]

Atlantification of Arctic ocean is causing a sharp increase in temperature and salinity around Svalbard Islands and in Kongsfjorden. Such phenomenon and the input of sediment-rich glacial meltwater influence salinity, water column turbidity, and light penetration with ecological implications on the microbial features. With the aim to address the temporal variability of the microbial assemblage in relation to environmental variables, a 7-day study was carried out in Kongsfjorden, in late summer 2013. Abiotic (temperature, salinity, nutrients, total suspended matter, particulate inorganic, and organic carbon) and biotic (phyto -, picophyto-, bacterio-, and virioplankton abundance and microbial respiration) parameters were investigated at a station in the inner fjord area, ca. 8.5 km away from the glacier front. Phyto-, picophyto-, and virioplankton showed low abundance. Dinoflagellates and coccolithophorids dominated the phytoplankton community while Synechococcus sp. the picophytoplankton alone, in relation with Atlantic water. Low virus to bacteria ratios were detected, presumably linked to the high sedimentation rates. Interesting variability for picophytoplankton with depth, virioplankton with both time and depth, and respiratory rates with time were found. Moreover, the organic matter turnover was slower on the first sampling day compared to that of the following days. Planktonic abundance depended on the variability of both hydrology (seawater mass inflow) and freshwater runoff from the glacier (relative turbidity degree). Differently, the metabolic rates of respiration appeared to be linked with the particulate carbon pool. Over 1-week study, the diverse microbial dynamics appeared to be conditioned on complex forcing, emphasizing the importance of high-resolution experiment. [ABSTRACT FROM AUTHOR]

Abstract: Viruses cause various diseases in humans through vector-borne (e.g., Zika and dengue fever), airborne (e.g., measles) and water-borne (e.g., hepatitis) transmission, as well as direct physical contact (e.g., AIDS and herpes). Recently, the new coronavirus (SARS-CoV-2) pandemic has triggered the greatest global health crisis in a century. However, not all viruses in nature are human enemies. A vast body of literature indicates that viral infection is vital for ecosystem functioning by affecting nutrient cycling, controlling species growth and enhancing biodiversity. Here we provide a perspective on the ecological role of viruses in nature, with special focus on Brazilian aquatic ecosystems.

Interest in coronaviruses because of the 2019 novel coronavirus (SARS-CoV-2) pandemic has generated concern about their occurrence and persistence in aquatic habitats. Coronaviruses are not quantitatively significant constituents of marine virioplankton. Members of the Nidovirales (to which human coronaviruses belong) infect marine mammals, teleosts and possibly invertebrates, and human coronaviruses may persist in marine plankton receiving wastewater effluent. However, virions likely experience significant particle and infectivity decay rates in surface seawater, similar to other enveloped RNA viruses.

Interest in coronaviruses because of the 2019 novel coronavirus (SARS-CoV-2) pandemic has generated concern about their occurrence and persistence in aquatic habitats. Coronaviruses are not quantitatively significant constituents of marine virioplankton. Members of the Nidovirales (to which human coronaviruses belong) infect marine mammals, teleosts and possibly invertebrates, and human coronaviruses may persist in marine plankton receiving wastewater effluent. However, virions likely experience significant particle and infectivity decay rates in surface seawater, similar to other enveloped RNA viruses. [ABSTRACT FROM AUTHOR]

Uncovering the role of environmental factors and finding critical factors which harbor significant fractions in governing microbial communities remain key questions in coastal marine systems. To detect the interactions between environmental factors and distributions of virio- and bacterioplankton in trophic coastal areas, we used flow cytometry to investigate the abundance of virio- and bacterioplankton covering 31 stations in the Bohai Sea of China. Our results suggested that the average abundance of total virus (TV) in winter (∼2.29×108 particles/mL) was slightly lower than in summer (∼3.83×108 particles/mL). The mean total bacterial abundance (TB) was much lower in winter (∼2.54×107 particles/mL) than in summer (∼5.43×107 particles/mL). Correlation analysis via redundancy analysis (RDA) and network analysis among virioplankton, bacterioplankton and environmental factors revealed that the abundances of viral and bacterial subpopulations depend on environmental factors. In winter, only temperature significantly influenced the abundances of virio- and bacterioplankton. In summer, in addition to temperature, both salinity and nutrient (SiO2) had a remarkable impact on the distribution of virio- and bacterioplankton. Our results showed a clear seasonal and trophic pattern throughout the whole water system, which revealed that temperature and eutrophication may play crucial roles in microbial distribution pattern. [ABSTRACT FROM AUTHOR]

Abstract Here we present our research results on the virioplankton of the shelf zone of the Kara Sea. This is the first study of viruses and bacteria done in the Kara Sea in early spring when viruses can play an important role in the abundance and production control of the bacterioplankton. All other studies cover July–September, that is, when the Kara Sea is completely ice-free and the community of viruses and bacteria is in an absolutely different stage of development. The samples were collected and processed on board of the vessel "Norilskiy Nickel" (project Aker ACS 650) between March 29 and April 8, 2016 on the regular cruise Murmansk – Dudinka. The abundance of bacteria (N B) and viruses (N V) located both underneath the ice and in the open waters of the Kara Sea and the Yenisei River estuary varied within a range of (0.075–0.429) × 106 cells × ml−1 and (0.30–2.11) × 106 viral particles × ml−1, respectively, and the N V /N B ratio varied from 2.6 to 15.4. A positive correlation was found between N B and N V (R = 0.70, p = 0.05). Viruses with capsid diameter of 16–297 nm were registered in the water samples examined. The transmission electron microscopy data show that the fraction of the virus-infected bacterial cells is about 0.2–2.3% of total N B. The mean viral-induced mortality of the bacteria calculated from all the sampling stations in the Kara Sea and the Yenisei River estuary was 7.8 ± 1.2% (with a range from 1.4 to 20.2%) of the daily bacterioplankton production. Our results show that viruses play an important role in the abundance and production of bacterioplankton control in early spring. [ABSTRACT FROM AUTHOR]

Abstract: The abundances of virioplankton and planktonic picocyanobacteria in deep and shallow water sites of Rybinsk Reservoir during the freezing period (water temperature 0.3-0.9°C) varied from (37.1 to 84.1) × 106 ((57.3 ± 2.1) × 106, on average) particles/ml and from 13.5 to 75.0 × 103 ((48.7 ± 3.4) × 103, on average) cells/ml, respectively. The fraction of picocyanobacteria with viruses attached to their cell surface was 6.5-29.0% (12.0 ± 0.8%, on average). The proportion of visible infected cells was 0.7-7.6% (2.2 ± 0.3%, on average) of the numbers of picocyanobacteria. It is likely that viruses play an important role in the regulation of picocyanobacteria abundance during the freezing period. [ABSTRACT FROM AUTHOR]

Abstract Marine viruses are dominated by phages and have an enormous influence on microbial population dynamics, due to lysis and horizontal gene transfer. The aim of this study is to analyze the occurrence and diversity of phages in the North Sea, considering the virus-host interactions and biogeographic factors. The virus community of four sampling stations were described using virus metagenomics (viromes). The results show that the virus community was not evenly distributed throughout the North Sea. The dominant phage members were identified as unclassified phage group, followed by Caudovirales order. Myoviridae was the dominant phage family in the North Sea, which occurrence decreased from the coast to the open sea. In contrast, the occurrence of Podoviridae increased and the occurrence of Siphoviridae was low throughout the North Sea. The occurrence of other groups such as Phycodnaviridae decreased from the coast to the open sea. The coastal virus community was genetically more diverse than the open sea community. The influence of riverine inflow and currents, for instance the English Channel flow affects the genetic virus diversity with the community carrying genes from a variety of metabolic pathways and other functions. The present study offers the first insights in the virus community in the North Sea using viromes and shows the variation in virus diversity and the genetic information moved from coastal to open sea areas. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Here we present a comprehensive review of the diversity revealed by research in limnology and microbial ecology conducted in Byers Peninsula (Livingston Island, South Shetland Islands, Antarctica) during the last two decades. The site constitutes one of the largest ice-free areas within the Antarctic Peninsula region. Since it has a high level of environmental protection, it is less human-impacted compared to other sites within the South Shetland archipelago. The main investigations in Byers Peninsula focused on the physical and chemical limnology of the lakes, ponds, rivers, and wetlands, as well as on the structure of their planktonic and benthic microbial communities, and on the functional ecology of the microbial food webs. Lakes and ponds in Byers range along a productivity gradient that extends from the less productive lakes located upland to the eutrophic coastal lakes. Their planktonic assemblages include viruses, bacteria, a metabolically diverse community of protists (i.e., autotrophs, heterotrophs, and mixotrophs), and a few metazooplankton species. Most of the studies conducted in the site demonstrate the strong influence of the physical environment (i.e., temperature, availability of light, and water) and nutrient availability in structuring these microbial communities. However, top-down biotic processes may occur in summer, when predation by zooplankton can exert a strong influence on the abundance of protists, including flagellates and ciliated protozoa. As a consequence, bacterioplankton could be partly released from the grazing pressure exerted by these protists, and proliferates fueled by external nutrient subsidies from the lake’s catchment. As summer temperatures in this region are slightly above the melting point of water, biotic processes, such as those related to the productivity of lakes during ice-free periods, could become even more relevant as warming induced by climate change progresses. The limnological research carried out at the site proves that Byers Peninsula deserves special attention in the framework of the research in extreme environments. Together with nearby sites, such as Signy Island, Byers Peninsula comprises a featuring element of the Maritime Antarctic region that represents a benchmark area relative to the global distribution and diversity of aquatic microorganisms.

Temporal and spatial changes of virioplankton abundance (VLP), chlorophyll-a (Chl-a) concentration, and some environmental variables, were assessed from October 2004 to April 2005 at four sampling sites in a high-mountain reservoir in the Colombian Andes. VLP ranged from 2.4-10.5×107 and 3.6- 6.5×107 VLP mL-1 in the samples from the photic zone and hypolimnion, respectively. Surface VLP showed a progressive increase from November to April in the limnetic zone, and until February in the littoral stations. This trend coincided with the gradual increase of the water column stratification, as well as the augment of the reservoir hydraulic volume. Principal components analysis showed a grouping of environmental (dissolved oxygen, pH, water temperature) and biological variables (VLP, Chl-a, bacterioplankton abundance and biomass) within the first component (26.4% of explained variance), associated to an increase of photosynthetic activity, as a potential supplement of organic substrates to heterotrophic viral hosts. High values of virus-to-prokaryote ratio (VPR), and a negative relationship between VLP and average biomass per prokaryotic cell, indicate strong viral control which is probably more intense on active and larger cells. These results provide a framework for understand the virioplankton responses to regional hydrological conditions and hydraulic behavior of this reservoir. The spatiotemporal scale of this study does not allow to confirm that viral dynamics is significantly affected by human activities causing potential alterations on nutrient cycling. [ABSTRACT FROM AUTHOR]

Virio- and picoplankton mediate important biogeochemical processes and the environmental factors that regulate their dynamics, and the virus-host interactions are incompletely known, especially in the deep sea. Here we report on their distributions and relationships with environmental factors at 21 stations covering a latitudinal range (2-23° N) in the Western Pacific Ocean. This region is characterized by a complex western boundary current system. Synechococcus, autotrophic picoeukaryotes, heterotrophic prokaryotes and virus-like particles (VLPs) were high (<2.4×10²-6.3×104, <34-2.8×10³, 3.9×104-1.3×106 cellsmL-1 and 5.1×105-2.7×107 mL-1, respectively), and Prochlorococcus were low (<2.3×10²-1.0×105 cellsmL-1) in the Luzon Strait and the four most southerly stations, where upwelling occurs. Covariations in the abundances of VLPs with heterotrophic and autotrophic picoplankton, and their correlation (i.e. r² =0.63 and 0.52, respectively) suggested a strong host dependence in the epi- and mesopelagic zones. In the bathypelagic zone, only abiotic factors significantly influenced VLPs abundance variation (r² =0.12). This study shows that the dynamics of virio- and picoplankton in this Western Pacific are controlled by suite of complex and depth-dependent relationship among physical and biological factors that in turn link the physical hydrography of the western boundary current system with microbial-mediated biogeochemical processes. [ABSTRACT FROM AUTHOR]

The abundance of virio-and bacterioplankton and the role of viruses in the mortality of heterotrophic bacteria have been studied in three different mire water bodies (lagg, hollow, and stream) in the Shichengskoe raised bog. The abundance of bacteria (up to 93 million cells/mL) and viruses (up to 152 million particles/mL) reached very high values. Considerable differences were found between the mire water bodies in seasonal dynamics and average values of the studied parameters. The ratio of the number of virioplankton to the number of bacterioplankton (median values from 1.3 in a hollow to 5.6 in a stream) is in low ranges of values which are available in literature sources. Viruses did not have a considerable direct effect on bacterioplankton while lysing ≤7.8% of the bacterial production. [ABSTRACT FROM AUTHOR]

Interactions of the main components of microbial planktonic food web (bacteria, heterotrophic nanoflagellates, and viruses) were studied in a protected overgrown littoral zone of the Rybinsk Reservoir (Upper Volga). The effect of colonial bird settlements (the Laridae family) on these processes was determined. The following systems exhibited significant negative correlations: 'heterotrophic nanoflagellates-large rod-shaped bacteria' ('predator-prey'), 'viruses-bacteriophages-bacterial products' ('parasite-host') and 'heterotrophic nanoflagellates-viruses-bacteriophages'. Relations between biotic factors controlling bacterial development were more pronounced outside the zone affected by colonial bird settlements. Near the bird colony the role of viruses in mortality of planktonic bacteria increased. Reproduction of bacterial cells accelerated in response to the increase in feeding activity of heterotrophic nanoflagellates. Virusesbacteriophages and heterotrophic nanoflagellates probably eliminate different targets until medium-sized cells become predominant in the bacterial community. Then heterotrophic nanoflagellates consume bacterial cells infected with viruses. [ABSTRACT FROM AUTHOR]

The results of ecological and phylogenetic studies of femtoplankton, the smallest size fraction of plankton formed by viruses and ultramicrobacteria (UMB), are overviewed to shed light on the problem of transbiome invasions by microbes. Phylogenetic lineages of viruses and UMB are shown to be associated with particular biomes, thus indicating infrequent transbiome transitions in the microbial world. An alternative hypothesis of widespread cross-colonization events requires a deeper analysis of the factors that form the barrier between biomes and are responsible for the adaptation of microorganisms to different environments. [ABSTRACT FROM AUTHOR]

In light of limited research into the relationship between the macroscale distribution and dynamic changes of microplankton in the shallow Bohai Sea, here we used flow cytometry to analyse samples collected from the Bohai Sea channel in winter and summer. Results showed that the average of both viral abundance (VA) and bacterial abundance (BA) were lower in winter (3.61 × 107 and 1.84 × 106 cells/mL, respectively) than in summer (7.47 × 107 and 5.05 × 106 cells/mL, respectively). At all 16 stations, VA was one order of magnitude greater than BA, with a positive relationship between one another. In the horizontal distribution, variations in VA and BA followed a similar trend, and both were obviously higher near-shore than offshore. In the vertical distribution, variations in both VA and BA did not show a clear relationship with water depth. VA and BA in summer were 2.1 and 2.7 times those in winter, respectively. Spearman correlation analysis showed that both VA and BA were correlated with the concentration of PO4-P in winter (positive) and NO3-N in summer (negative). Additionally, BA showed a negative correlation with salinity. It is clear that the macroscale distribution of these two kinds of microbes in the Bohai Sea is related to seasonal variation and nutrient availability. [ABSTRACT FROM AUTHOR]

The viral and bacterioplankton communities of the Barents Sea were investigated using a combination of methods of electron and epifluorescence microscopy for the first time. The quantitative composition of the communities and the nature of their interactions were also determined. Our study showed that during the summer the abundance and biomass of bacterioplankton reached 0.4-4.0 × 10 cells/mL and 25.09-84.21 mg/m in offshore waters and 0.4-1.8 × 10 cells/mL and 19.63-100.19 mg/m in coastal waters, respectively. In both regions, the number of viruses (1.7-35.8 × 10 and 14.5-32.4 × 10 particles/mL) exceeded the number of bacteria by 2-31 and 13-60 times, respectively; the average viral production was 0.7510 and 1.74 × 10 particles/mL/day, respectively. The proportion of infected cells in the total bacterioplankton (7% on average) and virus-induced mortality of bacteria (8%) were much lower in offshore than in coastal waters (14 and 20%, respectively). [ABSTRACT FROM AUTHOR]

By using flow cytometry techniques, we investigated the abundance and composition of the heterotrophic prokaryotes, virioplankton and picophytoplankton community in the Pearl River Estuary and Daya Bay in the summer of 2012. We identified two subgroups of prokaryotes, high nucleic acid (HNA) and low nucleic acid (LNA), characterized by different nucleic acid contents. HNA abundance was significantly correlated with larger phytoplankton and Synechococcus (Syn) abundance, which suggested the important role of organic substrates released from primary producers on bacterial growth. Although LNA did not show any association with environmental variables, it was a vital component of the microbial community. In contrast to previous studies, the total virioplankton concentration had a poor relationship with nutrient availability. The positive relationship between large-sized phytoplankton abundance and the V-I population confirmed that V-I was a phytoplankton-infecting viral subgroup. Although the V-II group (bacteriophages) was dominant in the virioplankton community, it was not related with prokaryotic abundance, which indicated factors other than hosts controlling V-II abundance or the uncertainty of virus-host coupling. With respect to the picophytoplankton community, our results implied that river input exerted a strong limitation to Syn distribution in the estuary, while picoeukaryotes (Euk) were numerically less abundant and showed a quite different distribution pattern from that of Syn, and hence presented ecological properties distinct from Syn in our two studied areas. [ABSTRACT FROM AUTHOR]

The effect of a colony of hydrophilic birds of the family Laridae on the dynamics of bacterioplankton, heterotrophic nanoflagellates, and extracellular virus particles is studied in the protected overgrown littoral of the Rybinsk Reservoir. Coastal waters of the reservoir are characterized by high quantitative characteristics of microorganisms and viruses. Compared to background parts, more pronounced variations in bacterioplankton biomass and an increase in the other quantitative characteristics of the planktonic microbial community during an intensive ornithogenic load are found in the areas occupied by bird colonies. [ABSTRACT FROM AUTHOR]

Bacterioplankton and phytoplankton dynamics, pelagic respiration, virioplankton abundance, and the diversity of pelagic diazotrophs and other bacteria were examined in relation to water-column nutrients and vertical mixing across the southern Great Barrier Reef (GBR) shelf where sharp inshore to offshore gradients in water chemistry and hydrology prevail. A principal component analysis (PCA) revealed station groups clustered geographically, suggesting across-shelf differences in plankton function and structure driven by changes in mixing intensity, sediment resuspension, and the relative contributions of terrestrial, reef and oceanic nutrients. At most stations and sampling periods, microbial abundance and activities peaked both inshore and at channels between outer shelf reefs of the Pompey Reef complex. PCA also revealed that virioplankton numbers and biomass correlated with bacterioplankton numbers and production, and that bacterial growth and respiration correlated with net primary production, suggesting close virus–bacteria–phytoplankton interactions; all plankton groups correlated with particulate C, N, and P. Strong vertical mixing facilitates tight coupling of pelagic and benthic shelf processes as, on average, 37% and 56% of N and P demands of phytoplankton are derived from benthic nutrient regeneration and resuspension. These across-shelf planktonic trends mirror those of the benthic microbial community. [ABSTRACT FROM AUTHOR]

Estuaries are important ecosystems providing irreplaceable services for humankind and, in turn, are extensively influenced by human activities and climate changes. Microbial processes, which are largely controlled by viruses, are always responsible for the ecological function and environmental problems in estuaries. However, we know little about the ecology and importance of viruses in estuarine systems. Here, we investigated viral ecological dynamics in estuarine systems on local (four largest estuaries in China in different seasons) and global scales. Viral production varied by almost 20-fold in Chinese estuaries with significant seasonality, being responsible for the removal of 1.41%-21.45% of the bacterioplankton standing stock each day, and contributed directly to the organic carbon pool by releasing an average of 3.57 µg of cellular carbon per liter per day. By compiling data from 21 estuaries across the world, we found for the first time that viral population size peaked at mid-latitude and viral production increased towards the equator in estuarine ecosystems. The results indicated the higher viral impact on microbial mortality and dissolved organic matter cycling in tropical estuaries. Our field investigation and global synthesized analysis provide compelling evidence of spatiotemporal variations in estuarine viral dynamics. The global view of viral impacts on estuarine microbial mortality offers important insight for incorporating viruses into ecological models and understanding the environmental implications of the tropicalization of temperate aquatic ecosystems under a scenario of climate warming., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflicts of interest., (Copyright © 2022 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Ice melting in the Antarctic summer and upwelling of the Circumpolar Deep Water (CDW) near the Antarctic continent have been suggested to regulate the distributions of microbial communities. However, an understanding of these relationships in the Indian Ocean sector of East Antarctica is lacking. We report on the distribution and relationships of virio- and picoplankton at 77 stations (including 29 stations throughout the entire water column and 48 stations from the epipelagic zone) from 35° to 78°E and 62° to 70°S, covering the Cosmonaut Sea, Cooperation Sea and Prydz Bay. The epipelagic stations were grouped into four clusters based on the virio- and picoplankton composition and abundance. Clusters three and four, which corresponded with areas of upwelling and ice retreat, had high abundances of autotrophic picoeukaryotes; this resulted in subsequent high abundances of heterotrophic prokaryotes and virioplankton. Cluster one and two stations correspond with a high nutrient, low chlorophyll (HNLC) area, where the abundances of autotrophic and heterotrophic picoplankton are low. Viruses were significantly correlated with heterotrophic prokaryotes in the ice-covered areas but more strongly correlated with autotrophic picoeukaryotes in areas associated with ice-edge blooms. Throughout the water column in the Cooperation Sea, nutrient supply from the upwelling of the CDW induced an increased abundance of heterotrophic prokaryotes, particularly in the meso- and bathypelagic zones of stations in the northern part of the area. High viral abundances were detected in the meso- and bathypelagic zones of stations with high abundances of virio- and picoplankton in the epipelagic zone. This study shows that the summer distribution of virio- and picoplankton in the Indian Ocean sector of East Antarctica was mainly controlled by ice-melting and upwelling of the CDW. [ABSTRACT FROM AUTHOR]

The influence of gull and heron colonies on the dynamics of heterotrophic bacteria, flagellates, and viruses in the coastal waters of the Rybinsk Reservoir is studied. The littoral zone of the reservoir is found to contain abundant microorganisms and virioplankton. The specifics of the seasonal dynamics of these components of the microbial community in the areas colonized by water birds are revealed. An increase in the abundance and biomass of bacteria has been found in open coastal waters near a heron colony, but not in the background biotope. Maximum values of these parameters are recorded in the protected part of the littoral near the nesting area of gulls. During the period of strong ornithogenic pressure, the abundance of microorganisms and viruses is higher in areas located near water-bird colonies. It is shown that gulls have the greatest influence on the microbial planktic community in the protected littoral zone separated from the open part of the reservoir and characterized by high concentrations of soluble organic compounds and nitrogen. [ABSTRACT FROM AUTHOR]

Virioplankton and picoplankton are the most abundant marine biological entities on earth and mediate biogeochemical cycles in the Southern Ocean. However, understanding of their distribution and relationships with environmental factors is lacking. Here, we report on their distribution and relationships with environmental factors at 48 stations from 112.5° to 150°W and 67° to 75.5°S in the Amundsen Sea of West Antarctica. The epipelagic stations were grouped into four clusters based on the virio- and picoplankton composition and abundance. Clusters three and four, which were associated with the ice-edge blooms in the coastal and Amundsen Sea Polynya (ASP) areas, had high abundances of autotrophic picoeukaryotes; this resulted in subsequent high abundances of heterotrophic prokaryotes and viruses. Cluster two stations were in open oceanic areas, where the abundances of autotrophic and heterotrophic picoplankton were low. Cluster one stations were located between the areas of blooms and the oceanic areas, which had a low abundance of heterotrophic prokaryotes and picoeukaryotes and a high abundance of virioplankton. The abundance of viruses was significantly correlated with the abundances of autotrophic picoeukaryotes and Chl- a concentration in oceanic areas, although this reflected a time-lag with autotrophic picoeukaryote and heterotrophic prokaryotes abundances in ice-edge bloom areas. The upwelling of Circumpolar Deep Water (CDW) might have induced the high abundance of autotrophic picoeukaryotes in the epipelagic zone, and the sinking particulate organic carbon (POC) might have induced the high abundance of heterotrophic prokaryotes and virioplankton in the meso- and bathypelagic zones. This study shows that the summer distribution of virio- and picoplankton in the Amundsen Sea of West Antarctica was mainly controlled by upwelling of the CDW and the timing of ice-edge blooms., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Han, Luo, He, Liang, Chen, Liu, Su, Ge, Yu, Zhao, Hao, Shao, Sung, Mok, Wong, McMinn and Wang.)

In order to understand the large-scale spatial distribution characteristics of picoplankton, nanophytoplankton and virioplankton and their relationship with environmental variables in coastal and offshore waters, flow cytometry (FCM) was used to analyze microbial abundance of samples collected in summer from four depths at 36 stations in the North Yellow Sea (NYS). The data revealed spatial heterogeneity in microbial populations in the offshore and near-shore waters of the NYS during the summer. For the surface layer, picoeukaryotes were abundant in the near-shore waters, Synechococcus was abundant in the offshore areas, and bacterial and viral abundances were high in the near-shore waters around the Liaodong peninsula. In the near-shore waters, no significant vertical variation of picophytoplankton (0.2-2μm) abundance was found. However, the nanophytoplankton abundance was higher in the upper layers (from the surface to 10 m depth) than in the bottom layer. For the offshore waters, both pico- and nanophytoplankton (2-20μm) abundance decreased sharply with depth in the North Yellow Sea Cold Water Mass (NYSCWM). But, for the vertical distribution of virus and bacteria abundance, no significant variation was observed in both near-shore and offshore waters. Autotrophic microbes were more sensitive to environmental change than heterotrophic microbes and viruses. Viruses showed a positive correlation with bacterial abundance, suggesting that the bacteriophage might be prominent for virioplankton (about 0.45μm) in summer in the NYS and that viral abundance might play an important role in microbial loop functions. [ABSTRACT FROM AUTHOR]

The spatial distribution of virio- and bacterioplankton and the role that viruses play in heterotrophic bacteria elimination was studied in the small Il'd' River (Rybinskoe Reservoir tributary, Upper Volga). The bacterioplankton abundance and biomass constituted 3.3-19.6 (8.5 on average) million cells/ml and 501-2353 mg/m (1054 mg/m on average), respectively. The highest abundance was registered for the shallow areas under anthropogenic and zoogenic load. The virus abundance varied from 7.4 to 66.9 million particles/ml, being 30.9 million particles/ml on average. The bacteria: virus ratio was in the range of 1.2-11.0 (4.0 on average); the maximal values were registered for the deepest parts of the river. One infected bacterial cell carried up to 45 virile phages. The virus-induced mortality (VIM) was in the range of 1.1-7.8% (3.7% on average) from daily bacterial production. These data evidenced a high abundance of bacterioplankton in the studied river and an insignificant impact of virus-mediated regulation on bacterial abundance and production. [ABSTRACT FROM AUTHOR]