The word `virus‘ is usually associ­ated with a parasitic life form that negatively impacts the host cell during infec­tion. However, viruses are far more than that. They are an essen­tial part of life, capable of infect­ing members of all three domains of life. One domain of partic­u­lar inter­est are the micro-organ­isms belong­ing to the domain of Archaea, since little is known about their inter­play between virus and host. Archaea and their viruses repre­sent a signif­i­cant part of micro­bial diver­sity on earth. It has been suggested that in some environ­ments dominated by archaea, half of the cells are infected by a virus at any given time point. It is there­fore very likely that a new virus will encounter an already infected cell, which would lead to compe­ti­tion for cellu­lar resources. To circum­vent this, some viruses have evolved the ability to block infec­tion of their host cell against super­in­fec­tion by the same or another closely related virus. This phenom­e­non is known as super­in­fec­tion exclu­sion (SIE). However, knowl­edge on super­in­fec­tion exclu­sion is still rather scarce, and the molec­u­lar mecha­nisms behind SIE have mainly been studied for viruses infect­ing bacte­ria. Such mecha­nisms still have to be unrav­eled for archaeal viruses. This project aims to provide a first insight into the require­ments for super­in­fec­tion exclu­sion in archaea, and would there­fore provide essen­tial infor­ma­tion to further inves­ti­ga­tion of the molec­u­lar mecha­nisms under­ly­ing this intrigu­ing phenom­e­non in haloar­chaeal viruses. To achieve this aim, I will use a combi­na­tion of qRT-PCR, fluores­cence and electron microscopy. 

Super­in­fec­tion: (A) Succes­full infec­tion with a virus (green). Virus attach either to surface filaments (1), travel to cell surface (2), or passage their genome over the cell membrane (3). The viral genome can be integrated into the host genome, also called lysogeny (4a), or repli­cate and form new virions (4b and 5), which are then released from the cell, e.g by cell lysis (7). (B) Inhibi­tion of Super­in­fec­tion: strat­egy of viruses to inhibit super­in­fec­tion by other viruses. The integrated virus may induce a genetic programme, that results in the inhibiton of super­in­fec­tion of similar (green) or differ­ent (orange) virions (6) for example by block­ing of phage-recep­tor (6a) or by alter­ation of cell surface (6b).