Abundance, morphology and distribution of planktonic virus-like particles in two high-mountain lakes

Abstract

Direct counts of virus-like particles (VLP) by transmission electron microscopy revealed abundances of up to 3 × 10⁷ ml⁻¹ in the plankton of two remote high-mountain lakes in the Alps and the Pyrenees. Most VLP were icosahedric without a tail, and with diameters between 40 and 90 nm, but very large ones with diameters of up to 325 run were also observed. VLP outnumbered bacteria by a factor of 4.2–42.8 and bacterial cells were infected with large numbers (>50) of viral particles. This study constitutes the first report on aquatic viruses for alpine lakes and it suggests that they may be an important additional source of bacterial mortality in these systems.