Taxonomy
The following genera and species are assigned to the family: * '' Alphalipothrixvirus'' ** '' Alphalipothrixvirus SBFV2'' ** '' Alphalipothrixvirus SFV1'' * '' Betalipothrixvirus'' ** '' Acidianus filamentous virus 3'' ** '' Acidianus filamentous virus 6'' ** '' Acidianus filamentous virus 7'' ** '' Acidianus filamentous virus 8'' ** '' Acidianus filamentous virus 9'' ** '' Sulfolobus islandicus filamentous virus'' * '' Deltalipothrixvirus'' ** '' Acidianus filamentous virus 2'' ** '' Deltalipothrixvirus SBFV3'' The family consists of three genera: ''Alphalipothrixvirus'', ''Betalipothrixvirus'', and ''Deltalipothrixvirus''. '' Captovirus'' used to be in this family as the genus Gammalipothrixvirus, but now it is the only genus in the family '' Ungulaviridae''.Häring M, Vestergaard G, Brügger K, Rachel R, Garrett RA, Prangishvili D (2005) Structure and genome organization of AFV2, a novel archaeal lipothrixvirus with unusual terminal and core structures. J Bacteriol 187(11): 3855–3858 {{doi, 10.1128/JB.187.11.3855-3858.2005 They are classified into genera based on their genomic properties and on the diversity of their terminal appendages, which are involved in host cell recognition. The originally proposed genus ''Alphalipothrixvirus'' was renamed ''Alphatristromavirus'' and moved to family ''Tristromaviridae''. In 2020, the genus ''Alphalipothrixvirus'' was recreated for classification of Sulfolobus filamentous virus 1{{cite journal , last1=Liu , first1=Y , last2=Osinski , first2=T , last3=Wang , first3=F , last4=Krupovic , first4=M , last5=Schouten , first5=S , last6=Kasson , first6=P , last7=Prangishvili , first7=D , last8=Egelman , first8=EH , title=Structural conservation in a membrane-enveloped filamentous virus infecting a hyperthermophilic acidophile. , journal=Nature Communications , date=2018 , volume=9 , issue=1 , pages=3360 , doi=10.1038/s41467-018-05684-6 , pmid=30135568, pmc=6105669 , bibcode=2018NatCo...9.3360L and Sulfolobales Beppu filamentous virus 2. In the genus ''Gammalipothrixvirus'' claw-like structures are found at either end of the virion. Members of the ''Lipothrixviridae'' share structural and genomic characteristics with viruses from the '' Rudiviridae'' family, which contains non-enveloped rod-shaped viruses. Viruses from the two families have linear dsDNA genomes and share up to nine genes. In addition, the filamentous particles of rudiviruses and lipothrixviruses are built from structurally similar, homologous major capsid proteins. Due to these shared properties viruses from the two families are classified into an order ''Virology
The viruses are enveloped and filamentous. The capsid varies considerably in length – 410–1950 nanometers (nm) – and is 24–38 nm in diameter. The envelope has a monolayer structure and includes di-phytanyl tetraethers lipids.{{cn, date=November 2022 From either end of the viron are protrusions extending from the core through the envelope. The capsid itself is elongated and exhibits helical symmetry. The core itself is helical.{{cn, date=November 2022 There are two major capsid proteins (MCP1 and MCP2). MCP1 and MCP2 form a heterodimer, which wraps around the linear dsDNA genome transforming it into A-form. Interaction between the genome and the MCPs leads to condensation of the genome into the virion superhelix.{{cite journal , last1=Wang , first1=F , last2=Baquero , first2=DP , last3=Beltran , first3=LC , last4=Su , first4=Z , last5=Osinski , first5=T , last6=Zheng , first6=W , last7=Prangishvili , first7=D , last8=Krupovic , first8=M , last9=Egelman , first9=EH , title=Structures of filamentous viruses infecting hyperthermophilic archaea explain DNA stabilization in extreme environments. , journal=Proceedings of the National Academy of Sciences of the United States of America , date=2020 , volume=117 , issue=33 , pages=19643–19652 , doi=10.1073/pnas.2011125117 , pmid=32759221, pmc=7443925 , doi-access=free Genomes are linear, up to 40 kb in length. {, class="wikitable sortable" style="text-align:center" , - ! Genus !! Structure , , Symmetry !! Capsid !! Genomic arrangement !! Genomic segmentation , - , ''Alphalipothrixvirus'', , Filamentous, , Helical, , Enveloped, , Linear, , Monopartite , - , ''Betalipothrixvirus'', , Filamentous, , Helical, , Enveloped, , Linear, , Monopartite , - , ''Deltalipothrixvirus'', , Filamentous, , Helical, , Enveloped, , Linear, , MonopartiteLife cycle
Viral replication is cytoplasmic. Entry into the host cell is achieved by adsorption to the host cell. Acidianus filamentous virus 1 was found to bind to cellular pili-like appendages. DNA templated transcription is the method of transcription. Archaea serve as the natural host. Transmission routes are passive diffusion. Virion assembly and egress have been studied in the case of Sulfolobus islandicus filamentous virus (SIFV). The virions assemble inside the cell. Binding of the major capsid protein dimers to the linear dsDNA genome lead to the assembly of nucleocapsids, which are subsequently enveloped intracellularly through an unknown mechanism.{{cite journal , last1=Baquero , first1=DP , last2=Gazi , first2=AD , last3=Sachse , first3=M , last4=Liu , first4=J , last5=Schmitt , first5=C , last6=Moya-Nilges , first6=M , last7=Schouten , first7=S , last8=Prangishvili , first8=D , last9=Krupovic , first9=M , title=A filamentous archaeal virus is enveloped inside the cell and released through pyramidal portals. , journal=Proceedings of the National Academy of Sciences of the United States of America , date=2021 , volume=118 , issue=32 , pages=e2105540118 , doi=10.1073/pnas.2105540118 , pmid=34341107, pmc=8364153 All lipothrixviruses are likely to be lytic viruses. In the case of betalipothrixviruses and deltalipothrixviruses, virions are released through pyramidal portals, referred to as virus-associated pyramids (VAPs). The VAPs of SIFV have a hexagonal base (i.e., constructed from six triangular facets). {, class="wikitable sortable" style="text-align:center" , - ! Genus !! Host details !! Tissue tropism !! Entry details !! Release details !! Replication site !! Assembly site !! Transmission , - , ''Alphalipothrixvirus'', , Archaea: ''Saccharolobus'', , None, , Injection, , Unknown, , Cytoplasm, , Cytoplasm, , Passive diffusion , - , ''Betalipothrixvirus'', , Archaea: ''Acidianus'', ''Saccharolobus'', , None, , Injection, , Lytic, , Cytoplasm, , Cytoplasm, , Passive diffusion , - , ''Deltalipothrixvirus'', , Archaea: ''Acidianus'', , None, , Injection, , Lytic, , Cytoplasm, , Cytoplasm, , Passive diffusionReferences
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