Bacteria and viruses in Arctic Sea ice

We studied vertical distribution of bacteria and viruses in different layers of the Arctic sea ice drilled at the North Pole. The sampled multi-year ice was characterized by uneven vertical distribution of bacterial abundance. This characteristic varied within the range of 8 ± 1.2 × 103 to 95 ± 2.6 × 103 cells mL–1. The layers with the maximal bacterial abundance were located in the intermediate and lower layers of the ice cores. Bacterial biomass varied from 0.5 to 5 mg C m–3 with the mean value 1.57 ± 0.2 mg C m–3. The ratio of viral to bacterial abundance varied from 0.6 to 28, with the mean value 12.5. The average total number of phages attached to bacteria was 6.2 × 103 viral particles mL–1. The number of viral particles located within the bacterial cells varied from 2 to 21 particles per a bacterial cell. The frequency of visibly infected bacterial cells (FVIC) calculated for the upper, intermediate and lower layers of the ice was 0.92, 1.23 and 0.8% of the total bacterial abundance, respectively. The overall frequency of infected cells (FIC) calculated for the same layers was 6.3, 8.4 and 0.8% of bacteria numbers, respectively, while the viral-mediated mortality of bacteria (VMB) was 7.1, 9.8 and 6.1%, respectively. Our data show that during the study period the rate of viral infection of bacterial cells and the viral-mediated mortality of bacterial cells in the multy-year ice of the North Pole were relatively low.