NLM DIR Seminar Schedule

Abstract:

Accumulation of massive amount of non-targeted sequencing data allows to reverse traditional virus discovery pathway. Classically, viruses were discovered as disease agents, isolated, sequenced, and analyzed. Later, similarities between these sequences were built into virus classification and given an evolutionary perspective. Nowadays, it became possible to discover previously unknown and undetected viruses directly from (meta)genomic sequences. Annotation is heavily assisted by availability of a large amount of related virus sequences, which increase the sensitivity and reduces dependence on external libraries of known domains and functions. This also facilitates classification and evolutionary reconstruction concurrent with the discovery.
I illustrate this using the discovery of mriyaviruses (proposed class (“Mriyaviricetes”), a group of small relatives of giant viruses (Nucleocytoviricota). The most intriguing feature of “Mriyaviricetes” is their putative ancestral status with respect to previously described Nucleocytoviricota, as indicated by their deep placement in phylogenetic trees of the conserved proteins and by comparison of the major capsid protein structures. Analysis of proteins encoded in mriyavirus genomes suggests that they replicate their genome via the rolling circle mechanism that so far was not described for members of Nucleocytoviricota. Further expansion of the “Mriyaviricetes” through extended metagenome mining can be expected to further clarify and solidify the scenario for the origin and evolution of the phylum Nucleocytoviricota and viral gigantism.