Susanne Erdmann:
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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.