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 How brains surrender to sleep
23.06.2017 | IMP - Forschungsinstitut für Molekulare Pathologie GmbH

nachricht A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>