bicaudaviridae bicaudaviridae bicaudaviridae is a family of hyperthermophilic archaeal viruses. members of the genus acidianus serve as natural hosts. there is only one genus (bicaudavirus) and one species in this family: acidianus two-tailed virus. however, sulfolobus tengchongensis spindle-shaped viruses 1 and 2 (stsv1 and stsv2) are regarded to belong to this family also. bicaudaviridae bicaudavirus virus classification (unranked): virus realm: incertae sedis kingdom: incertae sedis phylum: incertae sedis class: incertae sedis order: incertae sedis family: bicaudaviridae genera bicaudavirus taxonomy the genus contains one genus, which contains one species: bicaudavirus acidianus two-tailed virus structure genome organization of acidianus two-tailed virus showing location, sizes and transcriptional direction of the putative genes viruses in bicaudaviridae are non-enveloped, with lemon-shaped geometries. genomes are circular dsdna molecules of around 48–76 kb in length. high-resolution structure was determined by cryo-em for sulfolobus monocaudavirus 1 (smv1) and a lower-resolution structure was determined for acidianus two-tailed virus (atv). virions of both viruses have helical symmetry, with continuous 7-start helices, composed of the single major capsid protein, forming both the tails and the spindle-shaped body. the major capsid protein structure and virion organization of bicaudaviruses are similar to those of archaeal viruses from the families fuselloviridae, thaspiviridae, halspiviridae and clavaviridae. genusstructuresymmetrycapsidgenomic arrangementgenomic segmentation bicaudaviruslemon-shapedhelical (c7)non-envelopedcircularmonopartite life cycle electron micrographs of different forms of acidianus two-tailed virus viral replication is cytoplasmic. entry into the host cell is achieved by attachment of the viral proteins to host receptors. dna-templated transcription is the method of transcription. diverse species of hyperthermophilic archaea from the order sulfolobales serve as the natural hosts. transmission routes are passive diffusion. it has been demonstrated that certain members of the family, namely, stsv2 and sulfolobus monocaudavirus 1 (smv1), induce cell gigantism by blocking the expression of the cell division genes and arresting the cell cycle in the s phase. the diameter of infected cells increases up to 20 times, resulting in 8,000-fold increase in volume compared to noninfected cells. genushost detailstissue tropismentry detailsrelease detailsreplication siteassembly sitetransmission bicaudavirusarchea: acidianusnoneinjectionbuddingcytoplasmcytoplasmpassive diffusion history this family was first described by the team led by d. prangishvili in 2005. the name is derived from the latin word 'bi' and 'cauda' meaning 'two-tail'.