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
http://www.biomedcentral.com/news/20040413/01

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