CHARACTERIZATION OF PLANKTONIC VIRUS-LIKE PARTICLES IN A FRENCH MOUNTAIN LAKE - METHODOLOGICAL ASPECTS AND PRELIMINARY-RESULTS

In this short communication, we describe a simple method to ultracentr ifuge and concentrate planktonic virus-like particles, for their exami nation with a transmission electron microscope. A description of diffe rent morphotypes of particles clearly assimilable to viruses is made i n plankton samples from the euphotic layer of a eutrophic lake (Lake A ydat), during its spring and summer development. The particles possess a tail and a 6-sided icosahedral capsid-head, with dimensions similar to those of phages already described in marine systems. The diversity of viral forms and their abundance (10 fold higher than that of bacte ria) in Lake Aydat, suggests a significant role in controlling bacteri al number in lakes.