HIGH-CONCENTRATIONS OF VIRUSES IN THE SEDIMENTS OF LAC GILBERT, QUEBEC

Viruses were found to be very abundant in the top layer of the sedimen ts of Lac Gilbert, Quebec. Viruses were extracted from the sediments u sing pyrophosphate buffer, and viruses from the diluted extracts were pelleted onto grids and enumerated using transmission electron microsc opy. Viral abundance in the sediments ranged from 6.5 x 10(8) to 1.83 x 10(10) ml(-1), which is 10- to 1,000-fold greater than the number ob served in the water column. This increase corresponds well with the 10 0- to 1,000-fold increase in bacterial abundance in the sediments. Vir al abundance differed significantly among the surface sediment samples taken at different bottom depths and among samples taken at different depths of the water column. Viral abundance also varied significantly between the oxic and anoxic zones of the water column and the sedimen ts. The virus-to-bacteria ratio varied greatly among the different sed iment sites but not among depths in the water column. Viral abundance in the water column was related to bacterial abundance and chlorophyll concentration, whereas viruses in the sediments were most abundant in sediments with high organic matter content. Elevated viral abundance and their erratic distribution in the sediments suggest that viruses m ight play an important role in sediment microbial dynamics.