Keeping up with Virus Taxonomy: viruses that infect archaea
Posted on June 26, 2024 by Clare Baker
Welcome back to Keeping up with Virus Taxonomy. In past editions we’ve taken you through a journey of discovering viruses that infect various microbes, including bacteria and fungi so let’s tackle another microbe shall we? For this edition of Keeping up with Virus Taxonomy, we’re looking at virus families that infect archaea.
Simuloviridae
All members of the Simuloviridae family infect halophilic archaea in the class Halobacteria. They are temperate viruses, which means that infection does not immediately result in cell death. The genomes of the viruses in this family were originally thought to be plasmids. Their name actually originates from this characteristic; ‘simulo’ is Latin for ‘pretend’ so Simuloviridae literally means ‘viruses pretending to be plasmids’.
Sphaerolipoviridae
This virus family also has a narrow host range, infecting haloarchaea in the class Halobacteria (phylum Euryarchaeota). Sphaerolipoviruses were isolated from hypersaline environments, such as solar salterns (shallow ponds used for making salt) and salt lakes, in Europe, Australia and Asia. Viruses in this family most probably bind to their hosts by spike complexes at the virion vertices. Adsorption rates are low, similar to those of many other haloarchaeal viruses.
Pleolipoviridae
Viruses belonging to the Pleolipoviridae family infect euryarchaeal Halorubrum, Haloarcula, Halogeometricum or Natrinema strains of archaea. Their genomes vary, and members of this family have circular single-stranded DNA, circular double-stranded DNA or linear double-stranded DNA. Virions are typically stable at high ionic strengths or even saturated NaCl, but some are sensitive to low levels of salt. It is not surprising, then, that members of the Pleolipoviridae family, like Sphaerolipoviruses, originate from hypersaline environments. Their name derives from the Greek ‘pleo’ meaning ‘many’ and the Greek ‘lipos’ meaning ‘lipid’.
Thaspiviridae
This is a tiny family of viruses, as it is comprised of single genus and species, Nitmarvirus NSV1. NSV1-like particles are frequently observed in marine environments that are particle-rich, suggesting a cosmopolitan distribution in marine ecosystems. Thaspiviruses infect archaea of the genus Nitrosopumilus, ammonia-oxidising archaea which play an important role in nitrification and carbon cycling. When these archaea are infected by Thaspiviruses their ammonia oxidation rate suffers which means that Thaspiviruses could have an impact on global carbon and nitrogen cycling.
Portogloboviridae
This virus family is slightly bigger, but not by much. The Portogloboviridae family includes two virus species which belong to a single genus. The two viruses in this family were identified in environmental samples collected from two hot springs in Beppu, Japan. It comes as no surprise then, that these viruses infect hyperthermophilic archaea. Interestingly, evidence of inter-viral conflicts has been found in the two Portogloboviruses. They carry mini CRISPR arrays that contain spacers targeting not just other viruses, but each other.
The International Committee on Taxonomy of Viruses (ICTV) is responsible for developing and maintaining a universal virus taxonomy. Known viruses are categorised into a classification scheme taking into consideration their physical and biological properties in combination with their phylogenetic relationships.
These two-page summaries of each chapter of the ICTV Report (a free resource published by the ICTV which provides an up-to-date description of virus taxonomy) are freely available in the Journal of General Virology, and are supported by the Microbiology Society. These summaries are known as ICTV Virus Taxonomy Profiles and describe the structure, replication and taxonomy of each virus order and family.