- Archaebacteria -- Viruses,
- Viruses -- Isolation -- Laboratory techniques,
- Thermophilic microorganisms,
- Archaebacteria -- Host-virus relationships
A mere 50 viruses of Archaea have been reported to date; these have been investigated mostly by adapting methods used to isolate bacteriophages to the unique growth conditions of their archaeal hosts. The most numerous are viruses of thermophilic Archaea. These viruses have been discovered by screening enrichment cultures and novel isolates from environmental samples for their ability to form halos of growth inhibition, or by using electron microscopy to screen enrichment cultures for virus-like particles. Direct isolation without enrichment has not yet been successful for viruses of extreme thermophiles. On the other hand, most viruses of extreme halophiles, the second most numerous archaeal viruses, have been isolated directly from hypersaline environments. Detailed methods for the isolation of viruses of extremely thermoacidophilic Archaea and extremely halophilic Archaea are presented in this manuscript. These methods have been extremely effective in isolating novel viruses. However, Archaea comprise much more than extreme thermoacidophiles and extreme halophiles. Therefore a vast pool of archaeal viruses remain to be discovered, isolated, and characterized, particularly among the methanogens and marine Archaea. Some suggestions for expansion of the described methods are discussed. We hope these suggestions will provide an impetus for future work on these and other Archaeal viruses.