Since the first organisms were isolated from hot springs, a large number of viruses were found in these geothermal active environments, most of them infecting Archaea. Archaeal viruses form a separate lineage from those of Eukarya and Bacteria often showing exceptional morphologies and genomic features. Most of the isolated archaeal viruses infecting members of the Crenarchaeota have been characterized regarding their genome, the structure of their virions and their influence on the host viability. Only a few, SIRV a rod-shaped and STIV an icosahedrical virus, have been subjected to more extensive studies.
This work investigates tailed spindle-shaped viruses that we have isolated from different geographical acidothermal, terrestrial hot springs and they primarily infect members of the genus Sulfolobales.
The wide distribution of these viruses was established and, moreover, genomic comparisons of viral variants are presented. STSV2 (Sulfolobus tengchongensis spindle-shaped virus), a large virus exhibiting one tail, has been studied in detail with respect to its host range, the virion structure and the relationship with host cells and, in particular, the CRISPR based immune system of the host.
Biochemical characterizations of viral proteins were performed to gain a better understanding of the persistence of these viruses under the harsh conditions of their habitats and the relationship with their hosts. In particular proteins of ATV (Acidianus two-tailed virus) were investigated and possible functions are proposed. This virus exhibits the exceptional property of undergoing a major extracellular morphological development of two tails that occurs independently of the host cells.
In addition, the response of the CRISPR (Clustered regularly interspaced short palindromic repeats) -Cas system of Sulfolobus species was investigated when challenged by different genetic elements. This adaptive immune system has a major impact on virus-host interactions. The adaptation mechanism, involving the uptake of fragments of genetic elements as spacer regions in CRISPR arrays was induced using an environmental virus mixture and, subsequently, by isolated viruses. Two distinct mechanisms of spacer acquisition were identified. Possible lines of future research into the adaptive immune systems are considered.