| Summary: | Viruses are ubiquitous, abundant and diverse members of the biosphere. Numerous sequencing projects focusing on isolated viruses and uncultured viral communities (metaviromes) have demonstrated that viruses harbor unprecedented genotypic richness. The genomics of some viruses, for example, tailed bacteriophages infecting several widely known hosts from moderate environments, has been studied relatively well. However, viruses are known to reside in various environments, including the extreme ones, and our knowledge on the genetic make-up of these viral populations is very superficial. In this PhD thesis, the genomics of the archaeal and bacterial viruses isolated from previously sparsely sampled extreme aquatic environments was studied. The genomes of altogether twenty haloarchaeal pleomorphic and tailed viruses from hypersaline environments as well as tailed bacteriophages from the sea ice were sequenced and analyzed. The largest portion of the genomic sequences was shown to encode proteins with no homologues in current databases emphasizing genetic distinctiveness of the studied viruses from the ones described previously. However, all tailed viruses from both hypersaline environment and sea ice were predicted to have a cluster of genes coding for functional analogues of virion assembly and structure components of other tailed phages. Overall arrangement of this gene cluster was conserved. Haloarchaeal pleomorphic viruses were also shown to share a conserved group of genes coding for the structural and hypothetical proteins. Based on the genome organization, haloarchaeal pleomorphic viruses were classified into three subgroups. The members of one of the subgroups were demonstrated to have an unusual genome type, consisting of single-stranded and double-stranded DNA regions. In one of the viruses switches between the regions were found to be associated with a conserved DNA motif. This genome type has not been reported previously for other viruses infecting prokaryotes. To conclude, annotation and analyses of the ...
|
|---|