Bioinformatics sheds light on evolutionary origin of Rickettsia virulence genes

Mar 12, 2009

Scientists from the Virginia Bioinformatics Institute (VBI) at Virginia Tech, the University of Maryland School of Medicine, and the University of Louisville have revealed that genes for a specific type of molecular secretion system in Rickettsia, a structure that is linked in many cases to virulence, have been conserved over many years of evolution.

The scientists compared the of 13 Rickettsia species to detect a highly conserved type IV secretion system. Type IV are membrane-spanning transporters that can act as syringes that inject virulence factors into the cells of their hosts (eukaryotes). Once introduced, these virulence factors compromise the host and may result in harmful disease, for example Legionnaires' disease (Legionella pneumophila) and ( burnetii). However, these secretion systems have not been implicated in human diseases caused by Rickettsia, including (R. prowazekii) and Rocky Mountain spotted fever (R. rickettsii). Type IV secretion systems are unique in their ability to transport and proteins into plant and animal cells. A possible role of the transporter that is not directly associated with virulence, such as , has been overlooked in Rickettsia.

Dr. Joseph Gillespie, a bioinformatician at the Virginia Bioinformatics Institute and leader of the study, remarked: "We have used the Rickettsia genomic information steadily accumulated over the past 10 years as a starting point to look in detail at the origin and function of Rickettsia virulence-like genes. The study reveals a highly conserved type IV secretion system across the 13 genomes investigated, some of which are, intriguingly, not known to cause disease in their invertebrate and vertebrate hosts."

In addition to the evolutionarily conserved nature of the Rickettsia type IV secretion system, informatics analysis revealed some unexpected properties, including of nearly half of its components. Gene duplication is very rare in Rickettsia genomes. By digging a little further, the team also identified three additional genes that likely contribute to the secretion system. Gillespie noted: "Because Rickettsia live inside their hosts at all stages of their life cycle, we are very limited in how we can characterize their genes. Researchers often have little choice but to apply related information from other bacteria that are easier to study." This often entails labor-intensive manual work that cannot currently be substituted by automated gene prediction methods. "Sometimes, the brain beats the algorithm," Gillespie added.

One of the major revelations of the sequence comparison is that the ancestor organism of the Rickettsia most likely acquired a virulence-like genetic locus from distantly related bacteria. The team speculates that this may have taken place while the ancestor was residing in a protozoan host.

Principal Investigator Bruno Sobral remarked: "Virulent species of Rickettsia are of great interest both as emerging agents of infectious disease and potential bioterror agents. However, a lot of intense laboratory work has failed to provide information that characterizes their virulence factors. Our comparative genomics approach sheds light on the evolution of Rickettsia virulence and provides a solid foundation for the future laboratory assessment of the function of the Rickettsia type IV secretion system."

Dr. Gillespie concluded: "Additional experimental evidence from recent studies suggests that some of the components of the Rickettsia type IV secretion system are indeed expressed, regulated and secreted. It is too early yet to know with certainty the precise mechanism of how the system operates but we now have a solid foundation for future work."

More information: Joseph J. Gillespie, Nicole C. Ammerman, Sheila M. Dreher-Lesnick, M. Sayeedur Rahman, Micah J. Worley, João C. Setubal, Bruno S. Sobral, Abdu F. Azad (2009) An anomalous type IV secretion system in Rickettsia is evolutionarily conserved. The paper is featured in the March 12, 2009 edition of the online publication PLoS ONE.

Source: Virginia Tech (news : web)

Explore further: Heaven scent: Finding may help restore fragrance to roses

Related Stories

Researcher tags genes linked to disc degeneration

Mar 11, 2009

( -- Lumbar disc degeneration is an uncomfortable condition that affects millions of people, but two University of Alberta researchers have identified some of the genes that are causing problems. ...

Space Research May Help Explain Salmonella Illness

Mar 11, 2009

( -- Salmonella bacteria research from two recent NASA space missions discovered key elements of the bacteria's disease-causing potential that hold promise for improving ways to fight food-borne infections on ...

Small molecules block cancer gene

Mar 10, 2009

Finding molecules that block the activity of the oncogene Stat 3 (signal transducer and activator of transcription) required screening literally millions of compounds, using computers that compared the structure of the cancer-causing ...

Structure mediating spread of antibiotic resistance identified

Jan 08, 2009

Scientists have identified the structure of a key component of the bacteria behind such diseases as whooping cough, peptic stomach ulcers and Legionnaires' disease. The research, funded by the Wellcome Trust and the Biotechnology ...

Recommended for you

Study on pesticides in lab rat feed causes a stir

Jul 02, 2015

French scientists published evidence Thursday of pesticide contamination of lab rat feed which they said discredited historic toxicity studies, though commentators questioned the analysis.

International consortium to study plant fertility evolution

Jul 02, 2015

Mark Johnson, associate professor of biology, has joined a consortium of seven other researchers in four European countries to develop the fullest understanding yet of how fertilization evolved in flowering plants. The research, ...

Making the biofuels process safer for microbes

Jul 02, 2015

A team of investigators at the University of Wisconsin-Madison and Michigan State University have created a process for making the work environment less toxic—literally—for the organisms that do the heavy ...

Why GM food is so hard to sell to a wary public

Jul 02, 2015

Whether commanding the attention of rock star Neil Young or apparently being supported by the former head of Greenpeace, genetically modified food is almost always in the news – and often in a negative ...

The hidden treasure in RNA-seq

Jul 01, 2015

Michael Stadler and his team at the Friedrich Miescher institute for Biomedical Research (FMI) have developed a novel computational approach to analyze RNA-seq data. By comparing intronic and exonic RNA reads, ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.