Marnaviridae is a family of positive-stranded RNA viruses in the order Picornavirales that infect various photosynthetic marine protists. Members of the family have non-enveloped, icosahedral capsids. Replication occurs in the cytoplasm and causes lysis of the host cell. The first species of this family that was isolated is Heterosigma akashiwo RNA virus (HaRNAV) in the genus Marnavirus, which infects the toxic bloom-forming Raphidophyte alga, Heterosigma akashiwo. As of 2021, there are twenty species across seven genera in this family, as well as many other related virus sequences discovered through metagenomic sequencing that are currently unclassified.
Interactions between members of the Marnaviridae family and their hosts have notable significance in marine ecology, and are also relevant within the aquaculture industry. HaRNAV and viruses from Bacillarnavirus are known to have roles in regulating dynamics and composition of their hosts’ blooms. An unclassified sequence, Baishivirus, has been suggested to be the possible pathogen of glass post-larvae disease, which is prevalent in shrimp aquaculture. Viruses detected in a cultured prawn species that had been affected by growth retardation disease have also been placed in Marnaviridae.
History
The name "marnaviridae" is based on its genome type (RNA virus - rnaviridae), together with the prefix "ma" being derived from the Latin word mare (sea).
The family was proposed following the discovery of an RNA virus (HaRNAV) that infects H. akashiwo off of the coast of British Columbia, which was the first report of a single-stranded RNA virus capable of causing cell lysis in phytoplankton.
HaRNAV was isolated from water collected in the Strait of Georgia in British Columbia, Canada, from a concentrated virus assemblage using the host H. akashiwo (NEPCC 522). It must not be confused with two other unrelated viruses that infect this host, H. akashiwo virus 01 (HaV-1, isolate: HaV53) in the genus Raphidovirus, and Heterosigma akashiwo nuclear inclusion virus (HaNIV).
Marnaviridae existed for multiple years with Marnavirus as the only genus and HaRNAV as the only species. After the usage of metagenomic analysis on the amino acid sequences of the capsid proteins and RdRp domains on viruses under the order Picornavirales, Marnaviridae was discovered to have a larger variety of viruses classified under it. Previously unassigned Labyrnavirus and Bacillarnavirus were also classified as genera under Marnaviridae.
Further metagenomic studies have yielded 653 Marnavirus-like sequences, prompting the proposal for a taxonomic reorganization to incorporate the new data into existing frameworks.
Taxonomy
The following genera are recognised:
Bacillarnavirus
Kusarnavirus
Labyrnavirus
Locarnavirus
Marnavirus
Salisharnavirus
Sogarnavirus
Classification
While Marnaviridae has several characteristics that are similar to those of other viruses in the broader Picornavirales order, members of Marnaviridae are placed through analysis of the RdRp sequence of amino acids. The seven genera of Marnaviridae are designated based on analysis of RNA-dependent RNA polymerase (RdRp) sequences and capsid amino acid sequences, species are listed under each genus.
Bacillarnavirus
The Bacillarnavirus species share 57.8-64.4% of RdRp and 29.1-33.4% of capsid amino acid sequences, when compared with each other within Bacillarnavirus. When compared with other genera of the family, they share 23.8-47.8% of RdRp and 18.3-29.4% of capsid sequences. Chaetoceros socialis forma radians RNA virus 1 Chaetoceros tenuissimus RNA virus 01 Rhizosolenia setigera RNA virus 01
Kusarnavirus
Kusarnavirus shares 25.4-48.2% of RdRp and 21.7-47.9% of capsid sequences, with other genera in the family. Astarnavirus
Labyrnavirus
Labyrnavirus shares 22.4-33.6% identities of RdRp and 17.1-22.5% of capsid sequences. It is a deep-branching taxon. Aurantiochytrium single-strand RNA virus 01
Locarnavirus
The Locarnavirus species share 52.4-59.1% identities of RdRp and 32.2-38.3% of capsid sequences, when compared with each other within Locarnavirus. When compared with other genera of the family, they share 24.0-48.2% of RdRp and 17.2-27.4% of capsid sequences. Jericarnavirus B Sanfarnavirus 1 Sanfarnavirus 2 Sanfarnavirus 3
Marnavirus
Marnavirus shares 22.4-30.3% of amino acid sequence identity of RdRp and 18.5-26.4% of capsid sequences. It is the most divergent and deeply branched taxon within the family. Heterosigma akashiwo RNA virus