Re-Discovery of : Genomic and Functional Analysis of Viruses from Isolates.

Giardiasis, caused by the protozoan parasite , is an intestinal diarrheal disease affecting almost one billion people worldwide. A small endosymbiotic dsRNA viruses, virus (GLV), genus , family , might inhabit human and animal isolates of . Three GLV genomes have been sequenced so far, and only one was intensively studied; moreover, a positive correlation between GLV and parasite virulence is yet to be proved. To understand the biological significance of GLV infection in , the characterization of several GLV strains from naturally infected isolates is necessary. Here we report high-throughput sequencing of four GLVs strains, from isolates of human and animal origin. We also report on a new, unclassified viral sequence (designed GdRV-2), unrelated to , encoding and expressing for a single large protein with an RdRp domain homologous to and . The result of our sequencing and proteomic analyses challenge the current knowledge on GLV and strongly suggest that viral capsid protein translation unusually starts with a proline and that translation of the RNA-dependent RNA polymerase (RdRp) occurs via a +1/-2 ribosomal frameshift mechanism. Nucleotide polymorphism, confirmed by mass-spectrometry analysis, was also observed among and between GLV strains. Phylogenetic analysis indicated the occurrence of at least two GLV subtypes which display different phenotypes and transmissibility in experimental infections of a GLV naïve isolate.