Enhanced Viral Activity in the Surface Microlayer of the Arctic and Antarctic Oceans

The ocean surface microlayer (SML), with physicochemical characteristics different from those of subsurface waters (SSW), results in dense and active viral and microbial communities that may favor virus–host interactions. Conversely, wind speed and/or UV radiation could adversely affect virus infection. Furthermore, in polar regions, organic and inorganic nutrient inputs from melting ice may increase microbial activity in the SML. Since the role of viruses in the microbial food web of the SML is poorly understood in polar oceans, we aimed to study the impact of viruses on prokaryotic communities in the SML and in the SSW in Arctic and Antarctic waters. We hypothesized that a higher viral activity in the SML than in the SSW in both polar systems would be observed. We measured viral and prokaryote abundances, virus-mediated mortality on prokaryotes, heterotrophic and phototrophic nanoflagellate abundance, and environmental factors. In both polar zones, we found small differences in environmental factors between the SML and the SSW. In contrast, despite the adverse effect of wind, viral and prokaryote abundances and virus-mediated mortality on prokaryotes were higher in the SML than in the SSW. As a consequence, the higher carbon flux released by lysed cells in the SML than in the SSW would increase the pool of dissolved organic carbon (DOC) and be rapidly used by other prokaryotes to grow (the viral shunt). Thus, our results suggest that viral activity greatly contributes to the functioning of the microbial food web in the SML, which could influence the biogeochemical cycles of the water columnEn prensa

Viral-mediated microbe mortality modulated by ocean acidification and eutrophication: Consequences for the carbon fluxes through the microbial food web

Anthropogenic carbon emissions are causing changes in seawater carbonate chemistry including a decline in the pH of the oceans. While its aftermath for calcifying microbes has been widely studied, the effect of ocean acidification (OA) on marine viruses and their microbial hosts is controversial, and even more in combination with another anthropogenic stressor, i.e., human-induced nutrient loads. In this study, two mesocosm acidification experiments with Mediterranean waters from different seasons revealed distinct effects of OA on viruses and viral-mediated prokaryotic mortality depending on the trophic state and the successional stage of the plankton community. In the winter bloom situation, low fluorescence viruses, the most abundant virus-like particle (VLP) subpopulation comprising mostly bacteriophages, were negatively affected by lowered pH with nutrient addition, while the bacterial host abundance was stimulated. High fluorescence viruses, containing cyanophages, were stimulated by OA regardless of the nutrient conditions, while cyanobacteria of the genus Synechococcus were negatively affected by OA. Moreover, the abundance of very high fluorescence viruses infecting small haptophytes tended to be lower under acidification while their putative hosts\u27 abundance was enhanced, suggesting a direct and negative effect of OA on viral–host interactions. In the oligotrophic summer situation, we found a stimulating effect of OA on total viral abundance and the viral populations, suggesting a cascading effect of the elevated pCO2 stimulating autotrophic and heterotrophic production. In winter, viral lysis accounted for 30 ± 16% of the loss of bacterial standing stock per day (VMMBSS) under increased pCO2 compared to 53 ± 35% in the control treatments, without effects of nutrient additions while in summer, OA had no significant effects on VMMBSS (35 ± 20% and 38 ± 5% per day in the OA and control treatments, respectively). We found that phage production and resulting organic carbon release rates significantly reduced under OA in the nutrient replete winter situation, but it was also observed that high nutrient loads lowered the negative effect of OA on viral lysis, suggesting an antagonistic interplay between these two major global ocean stressors in the Anthropocene. In summer, however, viral-mediated carbon release rates were lower and not affected by lowered pH. Eutrophication consistently stimulated viral production regardless of the season or initial conditions. Given the relevant role of viruses for marine carbon cycling and the biological carbon pump, these two anthropogenic stressors may modulate carbon fluxes through their effect on viruses at the base of the pelagic food web in a future global change scenario

Impacto del virioplancton sobre las comunidades bacterianas en sistemas marinos

Memoria de tesis doctoral presentada por Julia Anna Boras para optar al grado de Doctora por la Universitat de Barcelona (UB), realizada bajo la dirección de la Dra. Mª Dolors Vaqué Vidal y la Dra. María Montserrat Sala Farré del Institut de Ciències del Mar (ICM-CSIC) y la Dra. Montserrat Vidal.-- 222 pages[EN] Viruses are a numerous and active element in all marine ecosystems, from coastal waters, through open sea, and to hydrothermal vents and the dark deep ocean layers. With concentrations of approximately 107 viruses per milliliter of seawater and 109 viruses per gram of soil or sediment (Wommack & Colwell 2000), they gain the status of the most abundant biological entities in the biosphere. Assuming that each virus contains roughly 10-17 grams of carbon, and a total number of viral particles in the ocean of 1030 (Suttle 2005), it can be calculated that they constitute the ocean second biomass (ca. 200 Mt) after bacteria (Hambly & Suttle 2005). Viruses also represent the largest reservoir of genetic diversity in the ocean (Rohwer 2003). [...][ES] Los virus son los entes más numerosos y activos de los ecosistemas aquaticos (marinos y de agua dulce), con abundancias de hasta 107 virus por mililitro de agua, o 109 virus por gramo de sedimento (Wommack & Colwell 2000). Debido a su abundancia, después de las bacterias, son las partículas responsables de una elevada biomasa en el océano (aprox. 200 Mt, Hambly & Suttle 2005), y probablemente representan el reservorio de diversidad genética más grande en el océano (Rohwer 2003).Peer Reviewe

The impact of ice melting on bacterioplankton in the Arctic Ocean

Global warming and the associated ice melt are leading to an increase in the organic carbon in the Arctic Ocean. We evaluated the effects of ice melt on bacterioplankton at 21 stations in the Greenland Sea and Arctic Ocean in the summer of 2007, when a historical minimum of Arctic ice coverage was measured. Polar Surface Waters, which have a low temperature and low salinity and originate mainly from melted ice, contained a very low abundance of bacteria (7.01 × 105 ± 2.20 × 105 cells ml-1); however, these bacteria had high specific bacterial production (2.40 ± 1.61 fmol C bac-1 d-1) compared to those in Atlantic Waters. Specifically, bacterioplankton in Polar Surface Waters showed a preference for utilizing carbohydrates and had significantly higher specific activities of the glycosidases assayed, i. e. β-glucosidase, xylosidase, arabinosidase and cellobiosidase. Furthermore, bacterioplankton in Polar Sea Waters showed preferential growth on some of the carbohydrates in the Biolog Ecoplate, such as d-cellobiose and N-acetyl-d-glucosamine. Our results suggest that climate change and the associated melting of Arctic ice might induce changes in bacterioplankton functional diversity by enhancing the turnover of carbohydrates. Since organic aggregates are largely composed of polysaccharides, higher solubilization of aggregates might modify the carbon cycle, weaken the biological pump and have biogeochemical and ecological implications for the future Arctic Ocean. © 2010 Springer-Verlag.Financial support was provided by the Spanish Ministry of Science and Innovation (MICINN) projects: ATOS (POL2006-00550/CTM) to C.M.D, STORM (CTM2009-09352) to M.M.S, and MICROVIS (CTM2007-62140) to D.V.J.A.B. was awarded a Ph.D. fellowship by the MICINN (FPU grant).Peer Reviewe

Determinación de la producción de virus como consecuencia de la lisis bacteriana

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Determinación de abundancia de virus por citometría de flujo

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Determinación de la producción de virus como consecuencia de la lisis bacteriana

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Determinación de la depredación bacteriana debida a protistas, mediante la desaparición en el tiempo de trazadores (bacterias marcadas con un compuesto fluorescente, FLB: fluorescent labeled bacteria)

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Enhanced Viral Activity in the Surface Microlayer of the Arctic and Antarctic Oceans

ASLO 2021 Aquatic Sciences Meeting, Aquatic Sciences for a Sustainable Future: Nurturing Cooperation, 22–27 June 2021The ocean surface microlayer (SML), with physicochemical characteristics different from those of subsurface waters (SSW), results in dense and active viral and microbial communities that may favor virus¿host interactions. Conversely, wind speed and/or UV radiation could adversely affect virus infection. Furthermore, in polar regions, organic and inorganic nutrient inputs from melting ice may increase microbial activity in the SML. Since the role of viruses in the microbial food web of the SML is poorly understood in polar oceans, we aimed to study the impact of viruses on prokaryotic communities in the SML and in the SSW in Arctic and Antarctic waters. We hypothesized that a higher viral activity in the SML than in the SSW in both polar systems would be observed. We measured viral and prokaryote abundances, virus-mediated mortality on prokaryotes, heterotrophic and phototrophic nanoflagellate abundance, and environmental factors. In both polar zones, we found small differences in environmental factors between the SML and the SSW. In contrast, despite the adverse effect of wind, viral and prokaryote abundances and virus-mediated mortality on prokaryotes were higher in the SML than in the SSW. As a consequence, the higher carbon flux released by lysed cells in the SML than in the SSW would increase the pool of dissolved organic carbon (DOC) and be rapidly used by other prokaryotes to grow (the viral shunt). Thus, our results suggest that viral activity greatly contributes to the functioning of the microbia