Subfamily: Twortvirinae

Genus: Twortvirus

Distinguishing features

There is only one species in this genus - Twortvirus Twort. The genome of its exemplar isolate -  Staphylococcus phage Twort (MT151386) is 139.7 kbp including 9.2-kbp terminal repeats. It encodes 175 proteins and one tRNA (Kwan et al., 2005, Głowacka-Rutkowska et al., 2020). Genes for 21 proteins are within the terminal repeats and thus are duplicated in the virion DNA. The only members of this genus infect Staphylococcus hyicus but not S. aureus (Łobocka et al., unpublished data). Earlier indications of S. aureus as a host were the result of misclassification of the relevant Staphylococcus hyicus strain as S. aureus (https://www.phage.ulaval.ca/?pageDemandee=souche&noSouche=1048&id=42&L=1).

Species demarcation criteria

There is only one species in the genus. New members of this species will be assigned based on their being more than 95% identical in genome nucleotide sequence, including the terminal repeat region. Phages with genomes that differ by more than 5% will be assigned to different species.