Post by Angie on Mar 2, 2006 10:38:36 GMT -5
www.sciencedaily.com/releases/2006/02/060219195554.htm
The Institute for Genomic Research
February 19, 2006
Ticks, Flukes, And Genomics: Emerging Pathogens Revealed
Ehrlichiosis is no star of science. This emerging disease has an awkward
name, vague flu-like symptoms, and a nasty habit of being caused by bacteria
that live inside ticks and flatworms. But in the current issue of the
journal Public Library of Science Genetics (PLoS Genetics), scientists put
ehrlichiosis under the genomic spotlight--and discover some brilliant
biology.
Led by scientists at The Institute for Genomic Research (TIGR) and The Ohio
State University (OSU), a team of researchers report the complete genomes of
three emerging pathogens that cause ehrlichiosis--Anaplasma phagocytophilum,
Ehrlichia chaffeensis, and Neorickettsia sennetsu--and compare the genomes
with those of 16 other bacteria with similar lifestyles. The study reports
new genes that allow the bacteria to evade a host's immune system, adapt to
new niches, and more. Finally, the report reconstructs the metabolic
potential of five representative genomes from these bacteria.
"By comparing so many different pathogens, some closely related and others
diverse, we're able to identify genes linked to different diseases and
organisms," explains molecular biologist Julie Dunning Hotopp of TIGR, first
author of the PLoS Genetics paper. Because the pathogens causing
ehrlichiosis are obligate intracellular bacteria--able to thrive only inside
host cells--they are hard to isolate and study in the lab, Hotopp adds. "How
are these diseases different? How are they the same? Can we correlate
certain genes with certain characteristics? For the first time, our
comparative genomics database offers a resource for tackling these
questions."
Recognized since at least the 1930s, ehrlichiosis sickens not only humans,
but also dogs, cattle, sheep, and other animals. In Japan, human
ehrlichiosis is commonly called sennetsu fever. In the U.S., most human
cases have been linked to ticks.
In the new study, scientists uncovered a clue to how ehrlichiosis-causing
bacteria infect such diverse animals. One of the three primary bacteria
sequenced, A. phagocytophilum, contains roughly 1,400 genes--including more
than 100 variations of a single gene that codes for a protein allowing the
bacteria to evade the immune system of the organism it has infected. This
protein sits on the bacteria's outer membrane surface. When the bacteria,
through tick bites, transfers to a human, say, or horse, the bacteria
chooses the protein variation needed to stay hidden from that particular
host.
"These genome sequences have revolutionized the types of experiments
[scientists] can perform to understand these diseases," says microbiologist
Yasuko Rikihisa of OSU's College of Veterinary Medicine. "Already, at least
four labs are performing, or planning to perform, whole genome DNA
microarray analysis and proteomic analysis of these bacteria."
In addition to comparing genomes, the current study used those genomes to
reconstruct the metabolic potential (the ability to use and produce energy
and compounds) of five bacteria, representing the numerous organisms
compared. With this final analysis, they gleaned new insight into the
broader tactics used by different bacteria. Ehrlichiosis pathogens, for
instance, appear capable of making vitamins that a host tick lacks in its
regular diet.
"This study is a beautiful example of how in-depth comparative genomics can
lead to the identification of molecular features that underlie the lifestyle
of pathogens," says TIGR molecular biologist Hervé Tettelin, senior author
of the PLoS Genetics article. "We could not have reached these conclusions
by independently studying the genome sequence of each individual pathogen,"
he adds. "Now we know how some of the pathogens studied infect or provide
benefits to their hosts."
The scientists hope to build on this work, with potential studies to
determine which bacterial genes are turned on during ehrlichiosis infection
and to track the evolutionary differences between ehrlichiosis-causing
organisms in different parts of the world. Other scientists can build on the
new work as well, by accessing the comparative database now online at
www.tigr.org/sybil/rcd/. This genome sequencing project work was
funded by the National Institutes of Health.
###
The Institute for Genomic Research is a not-for-profit center dedicated to
deciphering and analyzing genomes. Since 1992, TIGR, based in Rockville,
Md., has been a genomics leader, conducting research critical to medicine,
agriculture, energy, the environment and biodefense.
Copyright © 1995-2006 ScienceDaily LLC
The Institute for Genomic Research
February 19, 2006
Ticks, Flukes, And Genomics: Emerging Pathogens Revealed
Ehrlichiosis is no star of science. This emerging disease has an awkward
name, vague flu-like symptoms, and a nasty habit of being caused by bacteria
that live inside ticks and flatworms. But in the current issue of the
journal Public Library of Science Genetics (PLoS Genetics), scientists put
ehrlichiosis under the genomic spotlight--and discover some brilliant
biology.
Led by scientists at The Institute for Genomic Research (TIGR) and The Ohio
State University (OSU), a team of researchers report the complete genomes of
three emerging pathogens that cause ehrlichiosis--Anaplasma phagocytophilum,
Ehrlichia chaffeensis, and Neorickettsia sennetsu--and compare the genomes
with those of 16 other bacteria with similar lifestyles. The study reports
new genes that allow the bacteria to evade a host's immune system, adapt to
new niches, and more. Finally, the report reconstructs the metabolic
potential of five representative genomes from these bacteria.
"By comparing so many different pathogens, some closely related and others
diverse, we're able to identify genes linked to different diseases and
organisms," explains molecular biologist Julie Dunning Hotopp of TIGR, first
author of the PLoS Genetics paper. Because the pathogens causing
ehrlichiosis are obligate intracellular bacteria--able to thrive only inside
host cells--they are hard to isolate and study in the lab, Hotopp adds. "How
are these diseases different? How are they the same? Can we correlate
certain genes with certain characteristics? For the first time, our
comparative genomics database offers a resource for tackling these
questions."
Recognized since at least the 1930s, ehrlichiosis sickens not only humans,
but also dogs, cattle, sheep, and other animals. In Japan, human
ehrlichiosis is commonly called sennetsu fever. In the U.S., most human
cases have been linked to ticks.
In the new study, scientists uncovered a clue to how ehrlichiosis-causing
bacteria infect such diverse animals. One of the three primary bacteria
sequenced, A. phagocytophilum, contains roughly 1,400 genes--including more
than 100 variations of a single gene that codes for a protein allowing the
bacteria to evade the immune system of the organism it has infected. This
protein sits on the bacteria's outer membrane surface. When the bacteria,
through tick bites, transfers to a human, say, or horse, the bacteria
chooses the protein variation needed to stay hidden from that particular
host.
"These genome sequences have revolutionized the types of experiments
[scientists] can perform to understand these diseases," says microbiologist
Yasuko Rikihisa of OSU's College of Veterinary Medicine. "Already, at least
four labs are performing, or planning to perform, whole genome DNA
microarray analysis and proteomic analysis of these bacteria."
In addition to comparing genomes, the current study used those genomes to
reconstruct the metabolic potential (the ability to use and produce energy
and compounds) of five bacteria, representing the numerous organisms
compared. With this final analysis, they gleaned new insight into the
broader tactics used by different bacteria. Ehrlichiosis pathogens, for
instance, appear capable of making vitamins that a host tick lacks in its
regular diet.
"This study is a beautiful example of how in-depth comparative genomics can
lead to the identification of molecular features that underlie the lifestyle
of pathogens," says TIGR molecular biologist Hervé Tettelin, senior author
of the PLoS Genetics article. "We could not have reached these conclusions
by independently studying the genome sequence of each individual pathogen,"
he adds. "Now we know how some of the pathogens studied infect or provide
benefits to their hosts."
The scientists hope to build on this work, with potential studies to
determine which bacterial genes are turned on during ehrlichiosis infection
and to track the evolutionary differences between ehrlichiosis-causing
organisms in different parts of the world. Other scientists can build on the
new work as well, by accessing the comparative database now online at
www.tigr.org/sybil/rcd/. This genome sequencing project work was
funded by the National Institutes of Health.
###
The Institute for Genomic Research is a not-for-profit center dedicated to
deciphering and analyzing genomes. Since 1992, TIGR, based in Rockville,
Md., has been a genomics leader, conducting research critical to medicine,
agriculture, energy, the environment and biodefense.
Copyright © 1995-2006 ScienceDaily LLC