6.7 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Baltimore classification | 7/7 | https://en.wikipedia.org/wiki/Baltimore_classification | reference | science, encyclopedia | 2026-05-05T09:06:57.533227+00:00 | kb-cron |
Before Baltimore classification was created, a variety of classification systems for viruses had been proposed, classifying viruses by host, structure, biochemical properties, and other characteristics. Baltimore classification was proposed in 1971 by virologist David Baltimore in a paper titled "Expression of Animal Virus Genomes" that was published in the academic journal Bacteriology Reviews (now named Microbiology and Molecular Biology Reviews). Baltimore focused on classifying animal viruses but effectively classified all viruses by their routes of information transmission from genomic nucleic acid to mRNA. The system initially contained the first six groups but was later expanded to include group VII after the discovery of dsDNA-RT viruses. Because of the utility of Baltimore classification, it came to be used alongside standard virus taxonomy, which is based on evolutionary relationships and governed by the International Committee on Taxonomy of Viruses (ICTV). Over time, the belief that Baltimore groups were monophyletic spread among virologists. This was reflected in taxonomies published by the ICTV and the National Center for Biotechnology Information, which for decades placed the Baltimore groups as informal higher ranks above official taxonomic ranks. From 1991 to 2017, virus taxonomy used a five-rank system ranging from order to species, with Baltimore classification used in conjunction. Outside of official taxonomy, supergroups of viruses joining different taxa were created over time based on increasing evidence of deeper evolutionary relations. The advancement of sequencing methods in the 21st century in particular made it possible to study virus evolution and diversity in greater detail. This enabled virologists to better understand the relationships between Baltimore groups and the evolutionary history of viruses. Consequently, in 2016, the ICTV began to consider establishing ranks higher than order as well as how the Baltimore groups would be treated among higher taxa. In two votes in 2018 and 2019, the ICTV established a 15-rank system ranging from realm to species. As part of this, the Baltimore groups for ssDNA, dsRNA, +ssRNA, –ssRNA, and RT viruses were incorporated into formal taxa. In 2019, the realm Riboviria was established and initially included all dsRNA, +ssRNA, and –ssRNA viruses. A year later, Riboviria was expanded to also include RT viruses. Within the realm, RT viruses are included in the kingdom Pararnavirae and the three other Baltimore groups in the kingdom Orthornavirae as defining traits of the kingdom's phyla. While –ssRNA viruses of Ribozyviria were initially classified in Riboviria, this was a clerical error that was fixed in 2020. A year later, Ribozyviria was established for HDV and its relatives. For ssDNA viruses, the realm Monodnaviria was established in 2020 to accommodate almost all ssDNA viruses, as well as dsDNA viruses descended from them. In 2026, however, Monodnaviria was split into four realms (Efunaviria, Floreoviria, Pleomoviria, and Volvereviria) based on evidence that its four kingdoms did not share common ancestry. In 1974, virologist Vadim Agol proposed an extension of Baltimore classification to encompass all possible means of genetic information transmission and describe the hierarchical routes of information transmission, including both expression and replication, rather than solely mRNA synthesis. In the expanded system, there are 35 classes, 17 superclasses, and six types of genetic information transfer. The system was revisited in 2021 by Koonin et al. in light of discoveries made since the 1970s. Known viruses occupy 13 classes, one of which is shared with cells, seven superclasses, and three types. A fourteenth class is occupied by F-like plasmids. Ambisense viruses occupy two classes simultaneously, though separate classes could be made for them. Most unoccupied classes are of DNA-RNA hybrids, which appear to be disfavored by evolution since it may be advantageous to convert such molecules to dsDNA, the molecule most suitable for genome replication. According to Koonin et al., viruses that belong to the unoccupied classes are unlikely to be discovered unless they are rare in nature.
== Notes ==
== References ==
=== Books cited === Cann A (6 March 2015). Principles of Molecular Virology. Academic Press. pp. 122–127, 151–156. ISBN 978-0-12-801955-9. Cotmore SF, Tattersall P (25 November 2005). "A Rolling-Hairpin Strategy: Basic Mechanisms of DNA Replication in the Parvoviruses". In Kerr J, Cotmore S, Bloom ME (eds.). Parvoviruses. CRC Press. pp. 171–185. ISBN 978-1-4441-1478-2. Fermin G (12 March 2018). "Virion Structure, Genome Organization, and Taxonomy of Viruses". In Tennant P, Fermin G, Foster JE (eds.). Viruses: Molecular Biology, Host Interactions and Applications to Biotechnology. Academic Press. pp. 35–46. doi:10.1016/B978-0-12-811257-1.00002-4. ISBN 978-0-12-811194-9. S2CID 89706800. Hartl DL (2018). Essential Genetics and Genomics. Jones & Bartlett Learning. p. 8. ISBN 978-1-284-15245-6. Kuhn JH (1 March 2021). "Virus Taxonomy". In Bamford DH, Zuckerman M (eds.). Encyclopedia of Virology. Academic Press. pp. 28–37. doi:10.1016/B978-0-12-809633-8.21231-4. ISBN 978-0-12-809633-8. PMC 7157452. Lostroh P (25 March 2024). "The Fundamentals of Molecular and Cellular Virology". Molecular and Cellular Biology of Viruses. CRC Press. pp. 11–13. ISBN 978-1-04-000533-0. Louten J (28 May 2022). Essential Human Virology. Academic Press. ISBN 978-0-323-91492-5. Manglik M (24 March 2024). Genomics, Genetic Engineering and Biotechnology Applications. EduGorilla Publication. pp. 17–18. ISBN 978-93-6984-122-6. Rampersad S, Tennant P (12 March 2018). "Replication and Expression Strategies of Viruses". In Tennant P, Fermin G, Foster JE (eds.). Viruses: Molecular Biology, Host Interactions and Applications to Biotechnology. Academic Press. pp. 55–82. doi:10.1016/B978-0-12-811257-1.00003-6. ISBN 978-0-12-811194-9. S2CID 90170103.
== Further reading == Baltimore D (September 1971). "Expression of Animal Virus Genomes". Bacteriol Rev. 35 (3): 235–241. doi:10.1128/MMBR.35.3.235-241.1971. PMC 378387. PMID 4329869. — David Baltimore's original paper in which Baltimore classification was first proposed Agol VI (October 1974). "Towards the System of Viruses". Biosystems. 6 (2): 113–132. Bibcode:1974BiSys...6..113A. doi:10.1016/0303-2647(74)90003-3. PMID 4613396. — Vadim Agol's paper in which he first proposed an extension of Baltimore classification
== External links == Media related to Baltimore classification at Wikimedia Commons