Identification of diverse RNA viruses in <i>Obscuromonas</i> flagellates (Euglenozoa: Trypanosomatidae: Blastocrithidiinae)

Trypanosomatids (Euglenozoa) are a diverse group of unicellular flagellates predominately infecting insects (monoxenous species) or circulating between insects and vertebrates or plants (dixenous species). Monoxenous trypanosomatids harbor a wide range of RNA viruses belonging to the families <i>Narnaviridae, Totiviridae</i>, <i>Qinviridae</i>, <i>Leishbuviridae,</i> and a putative group of tombus-like viruses. Here, we focus on the subfamily Blastocrithidiinae, a previously unexplored divergent group of monoxenous trypanosomatids comprising two related genera: <i>Obscuromonas</i> and <i>Blastocrithidia</i>. Members of the genus <i>Blastocrithidia</i> employ a unique genetic code, in which all three stop codons are repurposed to encode amino acids, with TAA also used to terminate translation. <i>Obscuromonas</i> isolates studied here bear viruses of three families: <i>Narnaviridae, Qinviridae</i>, and <i>Mitoviridae</i>. The latter viral group is documented in trypanosomatid flagellates for the first time. While other known mitoviruses replicate in the mitochondria, those of trypanosomatids appear to reside in the cytoplasm. Although no RNA viruses were detected in <i>Blastocrithidia</i> spp., we identified an endogenous viral element in the genome of <i>B. triatomae</i> indicating its past encounter(s) with tombus-like viruses.