Year: 2016
Type: dissertation
Abstract: Viruses are significant biological, ecological, and evolutionary players, which are present virtually in all types of environments where cellular life is found. It has been suggested that one way to systematize the enormous virus diversity is to group viruses based on their virion architectural principles. Indeed, in spite of the overwhelming genetic diversity, all the known viruses display a limited number of morphotypes, and thus may be grouped into a limited number of structure-based lineages. To test how far virus structural conservation extends, new virus-host systems are needed to be isolated and characterized. Hypersaline environments, where halophilic archaea often dominate, are a rich source of new viruses. Currently, viruses that infect archaea are very little studied, as only ~100 archaeal viruses have been isolated. The aim of this thesis work was to isolate new archaeal viruses from hypersaline environments. In total, 36 new viruses were isolated from salt samples collected from the Samut Sakhon saltern (Thailand¬). These isolates displayed four previously known morphotypes: myovirus-like (27 isolates), siphovirus-like (4), tailless icosahedral (1), and pleomorphic (4). Among the obtained viruses, myoviruses had the widest host ranges (up to 14 hosts), infecting archaeal strains isolated from the same location or other hypersaline environments. Two of the isolated viruses, Haloarcula californiae icosahedral virus 1 (HCIV-1) and Haloarcula hispanica pleomorphic virus 3 (HHPV3), were characterized in molecular detail. The characterization included studies on virus infectivity under various conditions, virus life cycle, virion structural components (proteins, lipids, and nucleic acids), and virus genome sequencing and annotation. HCIV-1 is closely related to the other tailless icosahedral viruses SH1, PH1, and HHIV-2 that infect halophilic archaea. The core virion components are highly conserved in these viruses and determine their place in the PRD1-adenovirus structural lineage. This lineage comprises viruses which are distributed world-wide and infect hosts from all three domains of cellular life. HHPV3 belongs to the group of archaeal pleomorphic viruses, which share virion organization and gene synteny, but may have different genome types (circular single-stranded DNA or circular/linear double-stranded DNA) and low similarity at sequence level. Pleolipoviruses also originate from distant geographical locations. This thesis work significantly increased the number of known archaeal viruses, from ~100 to ~140, and provided insights into molecular details of the two new halophilic archaeal viruses. The limited number of observed virus morphotypes and the conserved architectural principles revealed in HCIV-1 and HHPV3 highlight that similar virus architectures are found from all over the planet, supporting the idea of viral structural lineages. Future sampling of various environments and more detailed studies on the currently available virus isolates will help to portray the true viral diversity.
Source: Työväentutkimus Vuosikirja
Author: Tatiana A. Demina
Language: English
Subfield: Virology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2549087822