Virus dynamics in a large epishelf lake (Beaver Lake, Antarctica)

Virus concentrations, virus-to-bacterium ratios (VBRs) and levels of lysogenic phage were measured throughout the 110-m water column of epishelf Beaver Lake during the austral summer of 2003/2004. The aim was to determine which factor(s) controlled viral dynamics using detailed concomitant published data on inorganic nutrients, chlorophyll a, dissolved organic carbon (DOC) and bacterial production for Beaver Lake (Freshwater Biology, 51, 2006, 1119). Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the bacterial community was also undertaken to investigate the potential relationship between bacterial community composition and viral dynamics. Virus concentration ranged between 1.43x104 and 302.4x104 virusesmL-1 and showed a clear increase over the summer, while bacterial concentrations exhibited no seasonal pattern (range: 9.6x104 to 44.6x104 cellsmL-1). Consequently, VBR varied with highest values in January (3.32-7.33). The percentage of lysogenic phage was low, ranging from 0 to 11.69%, suggesting that other life cycles (i.e. lytic or possibly pseudolysogeny) were taking place. Attempts to measure viral production using both the TdR incorporation technique and the dilution technique failed to produce consistent results, in common with other ultra-oligotrophic Antarctic lakes. There were significant correlations between viral concentration and each of chlorophyll a, DOC, ammonium and nitrate concentrations and bacterial production, but not between bacterial abundance and either soluble reactive phosphorus or temperature. Lack of change in the dominant bacterial community composition over summer suggests that changes in viral concentrations were a function of changes in other biological and physicochemical factors, rather than changes in host/phage infection. The results suggest a significant connection between viruses and bacteria, with the DOC pool acting as a conduit for the movement of carbon between the two components.