Viruses in the water column and the sediment of the eastern part of the Laptev Sea

Abstract

The distribution of viruses and their impact on prokaryotes were studied using the epifluorescence and transmission electron microscopy along a transect, located at 130°E from the area adjacent to the Lena River delta next to the shelf area, the continental slope area and the deep-sea regions of the Laptev Sea in September 2015. The abundance of planktonic prokaryotes (NP) and free viral particles (NV), the frequency of visibly virus-infected prokaryotic cells (FVIC), and the viral-mediated prokaryotic mortality (VMP) varied within the following ranges: (0.1–3.1) × 106 cells mL−1, (0.1–4.4) × 106 viruses mL−1, 0.3–1.7% of NP, and 2.1–12.2% of the total mortality of prokaryotes, respectively, and reached maximum values at the inner shelf area. The percentage of viruses attached to prokaryotic cells varied from 2 to 6% of NV in the surface waters of the outer shelf and the deep-sea areas to 43–46% at the depth of 100–140 m in the continental slope area. The percentage of viruses that were attached to detrital or mineral microparticles varied from less than 1% in the waters of the deep-sea area to 27–50% in the waters of the inner shelf area adjacent to the Lena River delta. A negative correlation was found between the fraction of lysogenic prokaryotes and the FVIC values (r = – 0.60, p < 0.05).In the 20-cm bottom water layer above the sediment the NP, NV, FVIC and VMP values were (0.8–3.0) × 106 cells mL−1, (1.6–3.4) × 106 viruses mL−1, 0.5–1.2%, and 3.7–9.5%, respectively. In the surface 2-cm layer of the sediment these parameters were (1.8–4.4) × 109 cells cm−3, (0.8–2.3) × 109 viruses cm−3, 0.2–1.0%, and 1.4–7.8%, respectively. In the bottom water layer the percentage of viral particles attached to prokaryotes and to detrital and mineral particles was 10–29% and 20–79% of NV, respectively. In the surface sediments the percentage of viral particles attached to prokaryotes was considerably higher compared to the bottom water layer and ranged from 44 to 57% of NV. The capsid size of the viral particles from the pelagic zone, bottom water layer and surface sediments was on average 71 ± 14, 74 ± 7 and 63 ± 7 nm, respectively. In all these habitats, viruses from the size class of 60–100 nm prevailed.The relatively high abundance of prokaryotes and viruses, as well as the high FVIC values in the freshwater-seawater mixing zone (the highest values were recorded in the waters with a salinity of 9.6 psu) were apparently caused by the influx of considerable amounts of nutrients, and dissolved and particulate organic matter that come with the river runoff. At the same time, the high concentration of small detrital and mineral particles in the freshwaters lead to considerable adsorption of viruses by these particles and caused a decrease in the FVIC in the coastal areas adjacent to the Lena River delta.