Eugene V Koonin1, Mart Krupovic2. 1. National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, USA. koonin@ncbi.nlm.nih.gov. 2. Institut Pasteur, Archaeal Virology Unit, Department of Microbiology, Paris, France. mart.krupovic@pasteur.fr.