science

Marnaviridae

Marnaviridae is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Marnaviridae rather than just read about it. In short: 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.

Key takeaways

Marnaviridae belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Marnaviridae to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Marnaviridae from memory before moving on to harder problems.

Reference excerpt

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.

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. Kusarnavirus shares 25.4-48.2% of RdRp and 21.7-47.9% of capsid sequences, with other genera in the family. Labyrnavirus shares 22.4-33.6% identities of RdRp and 17.1-22.5% of capsid sequences. It is a deep-branching taxon. 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. 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. The Salisharnavirus species share 35.6-63.6% of RdRp and 24.9-34.4% of capsid sequences, when compared with each other within Salisharnavirus. When compared with other genera of the family, they share 24.3-47.2% of RdRp and 18.2-31.5% of capsid sequences. The Sogarnavirus species share 48.8-77.0% of RdRp and 27.6-59.0% of capsid sequences, when compared with each other within Sogarnavirus. When compared with other genera of the family, they share 24.3-47.2% of RdRp and 17.1-47.9% for capsid sequences. Additionally, there are 653 virus sequences that have been identified (via metagenomic analysis) as possibly belonging to the family Marnaviridae. However, these sequences are not assigned under any of the existing genera.

Characteristics

Structure

Virions in Marnaviridae are non-enveloped, with icosahedral geometries, and T=pseudo3 symmetry. Virus particles are 22-35 nm in diameter. The capsid consists of three major capsid proteins (MCPs: VP1, VP2, VP3), each having a Jelly roll fold. Most species also encode a minor capsid protein (mCP: VP4). All VPs are composed of β-sheets and α-helices. that is located around the five-fold axes on the inside of the capsid. The structures of Chaetoceros socialis forma radians RNA virus 1 (CsfrRNAV01, Bacillarnavirus) and Chaetoceros tenuissimus RNA virus type II (CtenRNAVII, Sogarnavirus) have been determined. In both species, VP1 surrounds the five-fold axes while VP2 and VP3 form the two- and three-fold axes. The jelly roll folds on the MCPs are non-canonical with VP1 having nine β-strands and VP2 and VP3 having seven. VP1 also contains a unique EF-loop connected to the extra β-strand in the jelly roll fold which protrudes from the surface of the virus particle. A CD-loop is also present on VP1 which obscures the canyon structure that binds host receptors in the related Picornaviridae family. Unlike other species, VP4 is not present in the CsfrRNAV01 capsid, although the corresponding gene still exists.

… excerpt ends here. Continue reading the full article.

Illustrations

Marnaviridae: Electron micrograph of Heterosigma akashiwo RNA virus (HaRNAV) particles. Scale 50 nm. — Electron micrograph of Heterosigma akashiwo RNA virus (HaRNAV) particles. Scale 50 nm.

Worked examples

Example 1 — a first encounter with Marnaviridae

Start with the simplest possible case. Write down what Marnaviridae claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Marnaviridae before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Marnaviridae ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Marnaviridae

In research: Marnaviridae appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Marnaviridae in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Marnaviridae is common in secondary-school and first-year university syllabi. It links to neighbouring topics Picornavirales, Virus families, so understanding it makes those chapters shorter.
In everyday life: Look for Marnaviridae outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Marnaviridae in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Marnaviridae means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Marnaviridae out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Marnaviridae in simple terms?

Why does Marnaviridae matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Marnaviridae?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Marnaviridae.