Archaeons are a group of organisms phylogenetically distinct
from bacteria and eukaryotes. They inhabit a range of extreme
conditions such as hydrothermal vents or anoxic environments
that are thought to reflect the conditions that existed on the
primordial earth. The recently discovered Nanoarchaeum equitans
represents a novel archaeon kingdom and grows in conjunction
with the crenarchaeon Ignicoccus. In the October 13 Proceedings
of the National Academy of Sciences, Elizabeth Waters and
colleagues at Diversa show that N. equitans is parasitic rather
than symbiotic and has evolved from a primitive ancestor instead
of reductively from a more complex form (Proc Natl Acad Sci USA,
DOI:10.1073/pnas.1735403100, October 13, 2003). Waters et al.
sequenced what turned out to be the smallest genome to date and
observed a circular chromosome only 490 kb long, with 552 coding
sequences covering 95% of the genome and containing little
noncoding or pseudogene sequence that would have suggested
reductive evolution. Functi