By sequencing the genome of the symbiotic bacterium
Sodalis, which lives off the major disease-transmitting insect, the
tsetse fly, researchers at Yale School of Medicine have come a step
closer to understanding how microbial pathogens cause disease.
Led by Serap Aksoy, professor in the Department of Epidemiology
and Public Health at Yale School of Medicine, the team was highly
interested in Sodalis because of its close relation to human
bacterial pathogens like E.Coli, Salmonella and Yersinia.
Published online December 15 in Genome Research, the study looked
at the genome in Sodalis, the second of three kinds of bacteria
known to aid the tsetse fly in feeding off the blood of its host.
The tsetse fly is one of many eukaryotes (animals) that live in
association with symbiotic microbes or bacteria. These animals
depend on the microbes for vital nutrients they can't otherwise
produce.
"We have been able to develop the first system to grow Sodalis in
vitro in the laboratory," said Aksoy. "We were then able to
genetically modify the symbiotic bacteria and put it back into the
tsetse fly to manipulate host traits or functions. Information on
the blueprint of this organism now gives us a better handle on this
applied strategy."
When the team sequenced the bacterial genome, they found the
hallmarks of an organism transitioning from a free-living state to a
symbiotic state. "It's a relatively young association between the
tsetse host and the bacterium," said Aksoy. "Surprisingly, Sodalis
has many of the same features of pathogenic bacteria, although it is
obviously a beneficial organism that poses no harm to the tsetse
host. We can now investigate how these potentially pathogenic
features function in a beneficial relationship. It has changed our
view of host pathogen characteristics."
Aksoy and her team also found that the genome itself, in terms of
physical structure and size, looks similar to free-living bacteria.
As relationships become symbiotic--more and more dependent on the
host--bacterial genomes usually begin to shrink, but in the case of
Sodalis, it is the same size as the free-living bacteria. It has the
largest number of pseudogenes, products with no function, of any
bacteria to date, again indicating its recent transition to a
symbiotic lifestyle.
"If we get rid of these symbiotic bacteria, the flies become
sterile, so understanding what they provide to the flies is very
important from a vector control point of view," Aksoy said. "The
sequence will be extremely helpful and will expand functional
studies. We have increased understanding of how Sodalis transitions
from a free-living to a symbiotic state."
###
Other authors on the study included Hidehiro Toh, Brian L. Weiss,
Sarah Perkin, Atsushi Yamashita, Kenshiro Oshima and Masahira
Hattori.
Citation: Genome Research, Published online December 15,
2005
Print Publication: February 2006.
Editor's Note: The original news release can be found here.