Amoebae: Hiding in Plain Sight: Unappreciated Hosts for the Very Large Viruses

Abstract

For decades, viruses have been isolated primarily from humans and other organisms. Interestingly, one of the most complex sides of the virosphere was discovered using free-living amoebae as hosts. The discovery of giant viruses in the early twenty-first century opened a new chapter in the field of virology. Giant viruses are included in the phylum Nucleocytoviricota and harbor large and complex DNA genomes (up to 2.7 Mb) encoding genes never before seen in the virosphere and presenting gigantic particles (up to 1.5 μm). Different amoebae have been used to isolate and characterize a plethora of new viruses with exciting details about novel viral biology. Through distinct isolation techniques and metagenomics, the diversity and complexity of giant viruses have astonished the scientific community. Here, we discuss the latest findings on amoeba viruses and how using these single-celled organisms as hosts has revealed entities that have remained hidden in plain sight for ages. Expected final online publication date for the Annual Review of Virology, Volume 9 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Evolution of giant pandoravirus revealed by CRISPR/Cas9

“…Giant viruses (GV) have genomes up to 2.8 megabases and form viral particles that can match in size some cellular organisms 1,2 . Their dsDNA genomes can encode more than 1000 genes, 70% of them corresponding to proteins unseen in any other organisms 2,3 . These genes are referred to as ORFans 4 .…”

Biochemical and structural characterization of an inositol pyrophosphate kinase from a giant virus

“…S1 ). However, it is likely viral IPK diversity is still underestimated; recent literature (Queiroz et al, 2022 ; Schulz et al, 2022 ) predicts that only a small fraction of both total NCLDV genomes and their amoeboid hosts have been identified. We should also take into account the likelihood of discovering hitherto unrecognized NCLDVs in thawing permafrost (Alempic et al, 2023 ; Jansson and Wu, 2022 ).…”

The consequences of viral infection on protists

“…However, many microorganisms successfully evade the phagocytic pathway and thrive within the amoebae, turning them into transmission vehicles or incubators and enabling various types of ecological relationships to occur, from symbiotic to parasitic 9 . Besides, their cell biology and active grazing behavior serve as a widely used infection route for giant viruses, although miscellaneous entry mechanisms have already been described for this phylum of viruses 10 , 20 , 21 . Given the substantial size of their viral particles, they can trigger phagocytosis in amoebae, creating entry opportunities 11 – 14 .…”