Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Salmonella bacteria sequenced

25.10.2001


Salmonella: two sequences are better than one
© SPL


Bugs behind typhoid and food poisoning give up genetic secrets.

Two teams have sequenced the genomes of two Salmonella bacteria. One is responsible for typhoid; the other causes food poisoning.

The genomes should lead to new ways to diagnose, treat and vaccinate against both diseases. Comparing the sequences should also clarify why the closely related bugs behave quite differently.



The two strains are called Typhi and Typhimurium. Typhi, the typhoid bug, infects only humans, attacking the liver, spleen and bone marrow. Gut-dwelling Typhimurium, a major cause of salmonella food poisoning, is much less fussy about where it sets up home. "It infects just about anything that walks or crawls on the face of the earth," says microbiologist Stanley Maloy of the University of Illinois at Urbana-Champaign.

Fatal flaw

Typhoid infects 16 million people each year and kills 600,000. Drug resistance is making matters worse. The Typhi team sequenced a strain from Vietnam that is resistant to several antibiotics.

The genome data should improve diagnostic tools, says team member Gordon Dougan of Imperial College, London. Typhoid is hard to diagnose because its symptoms resemble those of other diseases, including malaria and dengue fever, and the bug is difficult to recognize.

Typhoid vaccines are not fully reliable, and are not included in infant vaccination programmes. "We need another step in vaccine progress," says Dougan.

The rewards for such a step could be great. "If we could block its transmission in humans, we could eradicate it altogether - it’s got nowhere else to go," says Julian Parkhill of the Sanger Centre in Cambridge, UK, leader of the Typhi genome project. Relying on human hosts has painted Typhi into an evolutionary corner.

Typhi’s genome gives a strong hint about its narrow tastes. The bacterium has more than 200 ’pseudogenes’ - once-functional stretches of DNA that have been inactivated by mutation. Working versions of these genes were discarded during Typhi’s evolution for its current habitat.

The more flexible Typhimurium, which presumably requires a bigger biological toolkit, has about 40 pseudogenes. Each bug also has hundreds of genes that are not found in the other. "For two organisms that are classified as a single species, the amount of difference is quite a surprise," says Parkhill.

Problem and solution

Typhimurium has a less alarming public image, but is a bigger health problem than typhoid, says Michael McClelland of the Sidney Kimmel Cancer Center in San Diego, California, who led the project to sequence Typhimurium.

"It’s thought to be at least 30-fold underreported. There are probably hundreds of millions of cases every year in the world," says McClelland. He adds that gut-dwelling Salmonella may kill twice as many people - mostly infants and the elderly - as typhoid.

Typhimurium’s sequence reveals 50 previously unknown genes that code for proteins on its surface. These are potential vaccine or drug targets.

The bug is a tool as well as a menace. Weakened versions are used to deliver vaccines and cancer drugs. In mice, Typhimurium’s symptoms are very similar to human typhoid, making it a laboratory favourite for salmonella research.

The team behind the Typhimurium genome has designed microchips to identify the genes that the organism switches on in different situations. These might explain how the bug lives in different hosts, and why it has different effects on humans and mice.

"It’s a double-whammy - we can design therapies and study Salmonella’s evolution," says Typhimurium team member Sandra Clifton of Washington University in St Louis, Missouri.

There are more than 2,000 recognized strains of Salmonella enterica, with a wide variety of hosts and disease-causing capabilities. The genomes of several more strains are in the pipeline - comparisons between types "will provide the very best clues as to how [host switches] can happen in bacteria", says Maloy.

References
  1. Parkhill, J. et al. Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18. Nature, 413, 848 - 852, (2001).

  2. McClelland, M. et al. The complete genome sequence of Salmonella enterica serovar Typhimurium LT2. Nature, 413, 852 - 856, (2001).


John Whitfield | Nature News Service
Further information:
http://www.nature.com/nsu/011025/011025-10.html
http://www.nature.com/nsu/

More articles from Life Sciences:

nachricht Topologische Quantenchemie
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

nachricht Topological Quantum Chemistry
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>