Virioplankton and virus-induced mortality of prokaryotes in the Kara Sea (Arctic) in summer

Abstract

Among the Arctic seas, the largest volume of river runoff (~45% of the total river-water inflow into the Arctic Ocean) enters the Siberian Kara Sea. The viral communities of the Kara Sea are important for the functioning of the marine ecosystem. Studies of virus–prokaryote interactions on the Kara Sea shelf have been conducted only in spring and autumn. Here, we investigated the abundance of free viruses, viruses attached to prokaryotes, and pico-sized detrital particles; the morphology (shape and size) of the viruses, viral infection and virus-mediated mortality of prokaryotes in early summer, i.e., during a seasonal ice melting period and maximum inflow of river-water volumes with high concentrations of dissolved and suspended organic carbon. Seawater samples for microbial analyses were collected across the Kara Sea shelf zone on board the Norilskiy Nickel as a research platform from June 29 to July 15, 2018. Abundances of prokaryotes (range (0.6–25.3) × 105 cells mL−1) and free viruses (range (10–117) × 105 viruses mL−1) were correlated (r = 0.63, p = 0.005) with an average virus: prokaryote ratio of 23.9 ± 5.3. The abundance of free viruses and viral-mediated mortality of prokaryotes were significantly higher in early summer than in early spring and autumn. Free viruses with a capsid diameter of 16–304 nm were recorded in the examined water samples. Waters in the Kara Sea shelf contained high concentrations of suspended organic particles 0.25–4.0 µm in size (range (0.6–25.3) × 105 particles mL−1). The proportions of free viruses, viruses attached to prokaryotes, and viruses attached to pico-sized detrital particles were 89.8 ± 6.0%, 2.2 ± 0.6% and 8.0 ± 1.3%, respectively, of the total virioplankton abundance (on average (61.5 ± 6.2) × 105 viruses mL−1). Viruses smaller than 60 nm clearly dominated at all studied sites. The majority of free viruses were not tailed. We estimated that an average of 1.4% (range 0.4–3.5%) of the prokaryote community was visibly infected by viruses, suggesting that a significant proportion of prokaryotic secondary production, 11.4% on average (range 4.0–34.0%), was lost due to viral lysis. There was a negative correlation between the abundance of pico-sized detrital particles and the frequency of visibly infected prokaryotic cells: r = −0.67, p = 0.0008.

The roles of river discharge and sea ice melting in formation of freshened surface layers in the Kara, Laptev, and East Siberian seas

“…Spreading and transformation of freshened surface layer in the Arctic Ocean influence many local physical, biological, and geochemical processes including biological productivity (Demidov et al, 2014;Mosharov et al, 2018;Kopylov et al, 2023), carbon cycle (Pipko et al, 2022), and transport of pollutants (Pogojeva et al, 2021;Yakushev et al, 2021). This fact highlights the importance of study of large-scale freshwater cycle in the Arctic Ocean.…”

Intense zonal freshwater transport in the Eurasian Arctic during ice-covered season revealed by in situ measurements

“…River runoff to the Arctic Ocean increased by 5–10% during the last century and is predicted to continue increasing in future as a result of the ongoing climate change 45 , 46 . The majority of this runoff increase occurs during winter and spring 47 and influences regional processes in the Kara and Laptev seas including plankton communities 48 – 52 , carbonate system 53 , 54 , and marine pollution 55 , 56 . This fact highlights the importance of study of large-scale freshwater cycle in the Arctic during ice-covered season, in particular, possible eastward alongshore advection of the Lena plume below sea ice, which remains unknown.…”

Significant differences in virioplankton structure and viral infection of bacteria in coastal and open waters of the western Laptev Sea (Arctic): influence of river discharge

“…2.4. Enumeration of Free-Living Viruses, Viruses Attached to Bacteria, and Viruses Attached to Suspended Particles 0.3-3.0 µm in Size Viruses were enumerated using transmission electron microscopy (TEM) as described previously [23,24]. Brie y, in glutaraldehyde-xed samples, the viruses, bacteria, and suspended particles ≤ 3 µm in size, contained in 50-mL samples, were harvested by centrifugation onto Pioloform (SPI, USA) and carboncoated 400-mesh nickel grids using an OPTIMA L-90k ultracentrifuge (Beckman Coulter, USA) at 100 000 × g for 2 h. Two grids were thus prepared for each water sample.…”