Haloarchaeal viruses: how diverse are they?

Hypersaline lakes are highly productive microbial environments that provide many advantages for microbial ecologists, including stable communities of relatively low diversity (mainly haloarchaea). An important component of these communities is comprised of their non-cellular parasites, i.e., their viruses. Few viruses of halobacteria (haloviruses) have been isolated and studied even though a wide selection of host species have been formally described (and easily cultured) for ten years. Hypersaline waters have been shown to contain very high concentrations of virus-like particles (at least 10(7) particles/ml), particularly fusiform particles, but laboratory isolations of new haloviruses have been very slow and the detailed study of selected examples even slower. Here we provide an outline of the reported haloviruses, including fusiform and unpublished isolates from this laboratory, and we discuss their diversity and the future directions for this research.