Tupanvirus is a genus of viruses first described in 2018.[1] The genus is composed of two species of virus that are in the giant virus group.[2][3] Researchers discovered the first isolate in 2012 from deep water sediment samples taken at 3000m depth off the coast of Brazil.[1] The second isolate was collected from a soda lake in Southern Nhecolândia, Brazil in 2014.[1] They are named after Tupã (Tupan), a Guaraní thunder god, and the places they were found. These are the first viruses reported to possess genes for amino-acyl tRNA synthetases for all 20 standard amino acids.[1][4][5]
The genus Tupanvirus was first described in 2018 with the discovery of the two isolates of tupanviruses found in soda lake and deep oceanic sediments samples collected in Brazil.[1] The genus is currently unassigned but hypothesized to be a member of the family Mimiviridae, along with the other amoeba-infecting viruses.[6] Members of the family Mimiviridae includes Acanthamoeba polyphaga mimivirus (APMV) that is known for its large size of ~500 nm in diameter.[6] In contrast, the typical virus size range is approximately 20-200 nm.[7] Mimiviruses also possess fibril structures on the capsid as well as genes encoding proteins for nucleotide synthesis and various metabolisms that are not found in other viruses.[8]
Unlike the other mimiviruses in the Mimiviridae, tupanvirus has a ~550 nm long cylindrical tail covered with fibrils that is attached to the base of the capsid.[6] This morphological feature makes tupanvirus the largest described virus (approximately ~ 1.2 μm in length with the tail) with the longest tail ever observed a in virus.[1][6] Tupanviruses are also capable of infecting a wider range of amoebae than other mimiviruses, and produce a cytotoxic effect in host and non-host organisms that is not observed in APMV.[6] In addition, phylogenomic results revealed that the genus Tupanvirus is separate from the other viruses in the family Mimiviridae.[6]
The morphology of Tupanvirus can be similarly compared to that of other ‘amoeba-infecting mimiviruses’.[6] This is because of similarities between the capsid of Tupanvirus and that of other amoebae-infecting mimiviruses.[1] The capsid of Tupanvirus measures approximately 450 nm.[6] One major difference is that the Tupanvirus virion presents a large cylindrical tail (~550 nm × 450 nm diameter) attached to the base of the capsid.[1] Both the capsid and cylindrical tail are covered in fibrils.[6] Tupanvirus can measure up to 1.2 μm in length, and some particles can reach up to 2.3 μm because of the “high degree of plasticity in the size of the tail”.[1][6] Also to note is a lipid membrane is seen within the capsid. Additionally, their capsid is described as having a ‘stargate structure’.[6] This star-shaped vertex is present in other mimivurises, and acts as a seal for the apex of the capsid.[9] It has also been stated that the tail of Tupanvirus is less electron dense than the capsid.[6]
The genome contains roughly 1.5 million base pairs of double-stranded DNA, coding for 1276–1425 predicted proteins, making it the fourth largest among viral genomes.[4] While 30% of the genes are new and not found in other viruses, genomic analysis shows most of the known genes can be related to amoeba-infecting mimiviruses, with the rest corresponding to eukaryotes and bacteria. The shared genes of tupanvirus with different lineages of amoeba-infecting mimiviruses indicate it as a separate genus within family Mimiviridae.[1] For example, its A/T rich genome resembles that of other amoebal mimiviruses and suggests a preference for codons formed by A/T-rich sequences. As well, the frequent occurrence of the “AAAATTGA” promoter motif is also similar to that of other mimiviruses.[1][10]