Noda-like RNA viruses infectingCaenorhabditisnematodes: sympatry, diversity and reassortment

Three RNA viruses related to nodaviruses were previously described to naturally infect the nematode Caenorhabditis elegans and its relative C. briggsae . Here we report on a collection of over 50 viral variants from wild-caught Caenorhabditis . We describe the discovery of a new related virus, the Mělník virus, infecting C. briggsae , which similarly infects intestinal cells. In France, a frequent pattern of co-infection of C. briggsae by the Santeuil virus and Le Blanc virus was observed at the level of an individual nematode and even a single cell. We do not find evidence of reassortment between the RNA1 and RNA2 molecules of Santeuil and Le Blanc viruses. However, by studying patterns of evolution of each virus, reassortments of RNA1 and RNA2 among variants of each virus were identified. We develop assays to test the relative potency and competitive ability of the viral variants and detect an interaction between host genotype and Santeuil virus genotype, such that the result of the competition depends on the host strain. Importance The roundworm Caenorhabditis elegan s is a laboratory model organism in biology. We study natural populations of this small animal and its relative C. briggsae and the viruses that infect them. We previously discovered three RNA viruses related to nodaviruses and here describe a fourth one, called the Melnik virus. These viruses have a genome composed of two RNA molecules. We find that two viruses may infect the same animal and the same cell. The two RNA molecules may be exchanged between variants of a given viral species. We study the diversity of each viral species and devise an assay of their competitive ability. Using this assay, we show that the outcome of the competition also depends on the host.