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

• Published in: PeerJ
• Main Authors: Kopylov, Alexander Ivanovich, Zabotkina, Elena Anatoliyevna, Sazhin, Andrey Fiodorovich, Romanova, Nadezda, Belyaev, Nikolay, Drozdova, Anastasia
• Other Authors: Russian Science Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: PeerJ 2023
• Subjects: Arctic; Arctic Ocean; Kara Sea
• Online Access: http://dx.doi.org/10.7717/peerj.15457; https://peerj.com/articles/15457.pdf; https://peerj.com/articles/15457.xml; https://peerj.com/articles/15457.html

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) × 10 5 cells mL −1 ) and free viruses (range (10–117) × 10 5 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) × 10 5 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) × 10 5 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 ...