Biography
In the popular press and even in the microbiological literature, representatives of Archaea have been considered a collection of "extemeophiles" and relegated to environments that seem harsh from the human standpoint. In fact, this perception is an artifact of the traditional requirement to culture microbes in order to detect and identify them. Since most microorganisms in nature, >>99%, are not cultivated readily or at all, the makeup of natural microbial diversity has been largely inaccessible. Over the past two decades, increasingly powerful molecular technologies have been used for culture-independent surveys of natural microbial diversity, and the results have expanded dramatically the inventory of phylogenetic diversity in all the three domains. The most extensive surveys have been conducted using SSU rRNA genes amplified by PCR from environmental DNA. Currently, archaeal environmental sequences in the databases outnumber those from cultivars by several-fold and span considerably more diversity (sequence space).
Inclusion of environmental sequences in phylogenetic calculations indicates that Crenarchaeota indeed constitute a coherent phylogenetic group, but Euryarchaeota may be less coherent than indicated by cultured sequences alone. The results highlight the uncertainties implicit in "deep phylogeny," but also point to the need for inclusion of environmental organisms, currently known only by sequences, if we are to achieve a comprehensive view of the diversity of Archaea.
