In the Quax group we are interested in interactions between archaea and their viruses. Archaea are ubiquitous microorganisms that form a separate domain of life. They can colonize very different environments ranging from the human gut and the world oceans to hydrothermal vents and hyper saline lakes. Compared with bacteria and eukaryotes, relatively little is known about the cell biology and ecological roles of archaea. A prominent feature of archaea is the extraordinary diversity of their viruses. Archaeal viral particles have many unique shapes not encountered for bacterial and eukaryotic viruses, such as a spindle, a spiral or a bottle. Viruses are estimated to outnumber their hosts at least by a factor ten, and therefore form a serious threat for archaeal cells. Archaeal viruses are important players in deep-sea ecosystems and biochemical cycles, as they are responsible for the cell-lysis induced release of considerable amounts of CO2. We focus on the infection strategies of archaeal viruses and study the molecular mechanisms underlying essential steps of the viral infection cycle, such as attachment, entry and release of the host cell. Since these processes take place at the cell surface, we are also actively studying the archaeal cell surface and surface appendages using the halophilic euryarchaeon Haloferax volcanii as a model. Studying the infection mechanisms of archaeal viruses can provide insight into the evolutionary history of viruses and help to understand adaptation to extreme environments.