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

Abstract

The warming of the Arctic causes increased freshwater input from rivers into the Arctic seas. A high concentration of suspended particulate material entering coastal water via river runoff considerably affects the structure of the viral community and viral infection and mortality of bacteria. The abundance, structure, and activity of planktonic viruses were assessed across zones subjected to varying degrees to Khatanga River runoff. The number of free-living, bacteria-attached, and particle-attached viruses, determined by transmission electron microscope, ranged from 9.6 to 86.3 × 105 viruses mL− 1, 0.3 to 4.9 × 105 viruses mL− 1, and 0.6 to 18.1 × 105 viruses mL− 1, respectively. The relative amount of free-living viruses in the total number of virioplankton varied from 40% in the mixed waters of Khatanga Bay to 94% in seawater of the continental slope. The abundance of free-living viruses was strongly negatively correlated with the abundance of suspended particles 0.3–210 µm in size. The frequency of visibly infected bacterial cells was strongly negatively correlated with the abundance of suspended particles with a size of 0.3–3.0 µm. The viral-mediated mortality of bacteria was 3.7–29.6% (on average 10.3 ± 0.8%) of bacterial production. The large amount of fine suspended particles contained in coastal waters of the western Laptev Sea appears to significantly reduce both the abundance of free-living viruses and ability of viruses to infect bacteria, due to the effective adsorption of viruses by these suspended particles.