We present an extension of the Minimum Information about any (x) Sequence (MIxS) standard for reporting sequences of uncultivated virus genomes. Minimum Information about an Uncultivated Virus Genome (MIUViG) standards were developed within the Genomic Standards Consortium framework and include virus origin, genome quality, genome annotation, taxonomic classification, biogeographic distribution and in silico host prediction. Community-wide adoption of MIUViG standards, which complement the Minimum Information about a Single Amplified Genome (MISAG) and Metagenome-Assembled Genome (MIMAG) standards for uncultivated bacteria and archaea, will improve the reporting of uncultivated virus genomes in public databases. In turn, this should enable more robust comparative studies and a systematic exploration of the global virosphere.

Eukaryotic single-stranded DNA (ssDNA) viruses are classified into 10 families (Table 1), but many remain unclassified (1, 2). Viruses from seven families (Bacilladnaviridae, Circoviridae, Geminiviridae, Genomoviridae, Nanoviridae, Redondoviridae, and Smacoviridae) have small circular genomes, with some encompassing only two genes, encoding the replication initiation protein (Rep) and the capsid protein (3–5). The genomes are replicated by the rolling-circle mechanism initiated by the virus-encoded Rep proteins of the HUH endonuclease superfamily (6–10). In eukaryotic ssDNA viruses, the HUH endonuclease domain is followed by a superfamily 3 helicase (S3H) domain, which is not found in prokaryotic ssDNA virus Reps, although homologous two-domain Reps are encoded by several groups of bacterial plasmids (5). Informally, this assemblage of ssDNA viruses has been referred to as “circular, Rep-encoding single-stranded (CRESS) DNA viruses” (4, 8). Viruses from the seven families infect hosts across the eukaryotic domain, including animals (Circoviridae), diatoms (Bacilladnaviridae), fungi (Genomoviridae), and plants (Nanoviridae and Geminiviridae), whereas members of the Smacoviridae and the newly created Redondoviridae have been discovered by metagenomics and are suspected to infect animals (3, 11), although an association of smacovirids with methanogenic archaea has also been suggested (12).