undetectable - 10^9 particles/ml
||Parikka KJ, Le Romancer M, Wauters N, Jacquet S. Deciphering the virus-to-prokaryote ratio (VPR): insights into virus-host relationships in a variety of ecosystems. Biol Rev Camb Philos Soc. 2017 May92(2):1081-1100. doi: 10.1111/brv.12271 p.1086 right column bottom paragraphPubMed ID27113012
||Le Romancer, M., Gaillard, M., Geslin, C. & Prieur, D. (2007). Viruses in extreme environments. Reviews in Environmental Science and Biotechnology 6, 17–31 AND Prangishvili, D., Forterre, P. & Garrett, R. A. (2006). Viruses of the Archaea: a unifying view. Nature Reviews Microbiology 4, 837–848 DOI: 10.1038/nrmicro1527PubMed ID17041631
||Abstract: "[Investigators] gathered data from 210 publications (and additional unpublished data) on viral ecology with the aim of exploring VPR [virus-to-prokaryote ratio]."
||P.1086 right column bottom paragraph: "Following the development of microbial ecology in recent decades, new possible niches have been explored, such as
so-called ‘extreme environments’. Although organisms from all three domains of life are found in extreme environments, bacteria and especially archaea are particularly abundant in
the harshest environments. Viral numbers from undetectable levels up to 10^9 particles/ml have been documented
(primary source Le Romancer et al., 2007) possibly mainly comprising archaeoviruses (primary source Prangishvili, Forterre & Garrett, 2006)."