Chlamydial evolution probed Species evolved within primitive
eukaryotic cells and had virulence factors now widespread By
Cathy Holding
The last common ancestor of the Chlamydiales group of
bacteria lived about 700 million years ago inside a
eukaryotic host cell, according to a new study. This
primeval chlamydia encoded many virulence factors now found
in modern pathogenic chlamydiae as well as in Salmonella and
Escherichia coli, according to the authors of the paper in
Science published on April 8, 2004.
Matthias Horn and colleagues at the University of Vienna
used the genome sequence of the group's recently discovered
closest living relative-an endosymbiotic chlamydia living in
amoebae-to reconstruct the genetic makeup of the last common
ancestor. Among the species' virulence factors, now found in
a wide range of bacterial pathogens, was a type III
secretion system-a mechanism by which bacteria can inject
their proteins into host cells in order to force the host
cells do something to the bacteria's advantage.
Horn showed that the sequence of the symbiotic chlamydia had
to be close to the ancient sequence. "We could see that the
genome was stable for many [millions of years because] we
didn't see any evidence for horizontal gene transfer," he
told The Scientist.
Read the rest at The Scientist
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