PRESENCE OF LARGE VIRUS-LIKE PARTICLES IN A EUTROPHIC RESERVOIR

The presence of large virus-like particles (LVLP) without tails was ob served in the water of a severely eutrophied freshwater reservoir. We used a transmission electron microscope coupled to a semiautomatic ima ge analysing system to study the size distribution of aquatic viruses. The LVLP had maximum head diameters between 195 and 210 nm. Although the affiliation and host of the LVLP are unknown, similarities in size and shape were found with the African swine fever virus. The diffuse organic contamination from piggeries in the catchment area may explain the presence of these LVLP. The observed overlap in size of the LVLP with the smallest bacteria implies serious methodological problems in distinguishing these communities under the epifluorescence microscope. Therefore, although at present we do not know how common LVLP are in other aquatic systems, we discourage the use of epifluorescence micros copy for viral abundance estimations during routine work.