without the need for cultivation of hosts,
which is the critical bottleneck in the study of archaeal
viruses. Additionally, metagenomic projects allow the identification
of further viruses. For example, a halovirus-like
sequence, EHP-1, has been recovered directly from a crystallizer
pond, although the virus itself has yet to be isolated (Santos
et al. 2007). Recently the genome of an apparently
archaeal virus from an extremely acidic acid mine drainage
site was cleverly determined by analysis of CRISPR sequences
in a metagenome databank (Andersson and Banfield, 2008).
The human gut metagenome project may also provide some
clues to the presence of currently undetected viruses of
Archaea. Methanogens are associated with gum disease (Lepp
et al. 2004) and have long been known to be in human gut
samples (e.g., Nottingham and Hungate 1968). Therefore, it is
highly likely that their viruses are also present.
Clearly, there is a great deal remaining to be discovered in
viruses of Archaea. Implementation and expansion of the
methods described and proposed herein should greatly stimulate
progress in the discovery, characterization and understanding
of this understudied group of viruses.