Nav: Home

Inflammation awakens sleepers

March 29, 2017

Bacteriophages (short form: phages) are viruses that infect bacteria. The "good" lytic phages kill off bacteria that are harmful to humans and are sometimes used in medicine; the "bad guys", the temperate phages, on the other hand, transfer their genes to microorganisms, thus giving them new properties, such as the ability to produce a toxin. The transfer of temperate phages is therefore regarded as an important driving force behind the development of bacteria into potent pathogens.

Using Salmonella, a common pathogen of gastrointestinal diseases, as an example, researchers led by ETH Professor Wolf-Dietrich Hardt have now shown that the body's own inflammatory response actually promotes the transfer of phage genes to the bacteria, thus increasing the pathogenicity of Salmonella. Their study has just been published in the specialist journal Science.

Highly efficient gene transfer

To find out how quickly temperate phages spread out within a Salmonella population, the researchers infected mice with two different strains of Salmonella. One strain carried the "SopEΦ" phage, while the other did not.

Salmonella triggered an inflammation in the animals' intestine, which led to a major change in the Salmonella strain carrying phage genes: the phage genes were expressed, the phage multiplied and ultimately free phage particles were released, killing the Salmonella cell. Free phages swarmed out and entered the second Salmonella strain to further increase there. In this way, the phages transferred their genes to almost all Salmonella cells of any strain that had previously been free of phage genes.

This horizontal gene transfer sometimes took only three days to complete. "The gene transfer is extremely efficient. That surprised us," says Hardt, who had not expected such a rapid spread of infection into naive Salmonella strains.

Virus is linked to an alarm system

"The efficiency of the procedure can be explained using previous knowledge gained from textbooks," says Médéric Diard, a postdoc in Hardt's group, who carried out the study. As soon as the bacteria cell is attacked by inflammatory factors such as reactive oxygen and nitrogen species, it sets off an SOS signal, which starts the cell's own repair programme. This signal is used as a wake-up by the phages lying dormant in the genome. "Our results show that the inflammation of the intestine promotes the horizontal gene transfer through phages - an important evolutionary mechanism of microorganisms," explains Hardt.

As long as the inflammation persists, the freshly infected Salmonella also produce more phages that in turn infect more Salmonella. This chain reaction can only be prevented if the adaptive immune system intervenes. It sends specific antibodies to neutralize Salmonella at the site of infection.

This risk of phage release can be alleviated by vaccination: Salmonella in vaccinated animals is prevented from triggering a bowel inflammation. Incidentally, this also prevents the SOS response and the production of phages.

Virus as a beneficiary

Médéric Diard proposed that phages could take "control" of the bacteria so that they trigger inflammation ever more efficiently. This also promotes phage reproduction n the intestine. This link may explain why many phages transfer toxin genes to the bacteria. Phage-encoded toxic substances may create the very conditions in the intestine of victims that stimulate phage production. "Phages are 'selfish'. Therefore one may regard Salmonella diarrhea as a collateral damage of phage evolution," says Hardt.

How the cholera bacterium became viciously successful

Cholera has become a dreadful cause of diarrhea worldwide. claimed many lifes. This was not always the case. The original ancestor of Vibrio cholerae was a harmless brackish water bacterium off the coast of Bangladesh. A phage infected these bacteria and integrated into their genome, including the cholera toxin. This turned the harmless bacterium into a powerful pathogen. The acquisition of the cholera toxin gene obviously provides this bacterium with an evolutionary advantage. Today, the bacterium has spread around the world and frequently causes epidemics, claiming many lifes, particularly after natural catastrophes or in areas of conflict where there is poor hygiene.
-end-
Reference

Diard M et al. Inflammation boosts bacteriophage transfer between Salmonella spp. Science 17 Mar 2017: Vol. 355, Issue 6330, pp. 1211-1215. DOI: 10.1126/science.aaf8451

ETH Zurich

Related Bacteria Articles:

Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.
How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.
The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?
Detecting bacteria in space
A new genomic approach provides a glimpse into the diverse bacterial ecosystem on the International Space Station.
Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.
Bacteria uses viral weapon against other bacteria
Bacterial cells use both a virus -- traditionally thought to be an enemy -- and a prehistoric viral protein to kill other bacteria that competes with it for food according to an international team of researchers who believe this has potential implications for future infectious disease treatment.
Drug diversity in bacteria
Bacteria produce a cocktail of various bioactive natural products in order to survive in hostile environments with competing (micro)organisms.
Bacteria walk (a bit) like we do
EPFL biophysicists have been able to directly study the way bacteria move on surfaces, revealing a molecular machinery reminiscent of motor reflexes.
Using bacteria to create a water filter that kills bacteria
Engineers have created a bacteria-filtering membrane using graphene oxide and bacterial nanocellulose.
Probiotics are not always 'good bacteria'
Researchers from the Cockrell School of Engineering were able to shed light on a part of the human body - the digestive system -- where many questions remain unanswered.
More Bacteria News and Bacteria Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Accessing Better Health
Essential health care is a right, not a privilege ... or is it? This hour, TED speakers explore how we can give everyone access to a healthier way of life, despite who you are or where you live. Guests include physician Raj Panjabi, former NYC health commissioner Mary Bassett, researcher Michael Hendryx, and neuroscientist Rachel Wurzman.
Now Playing: Science for the People

#544 Prosperity Without Growth
The societies we live in are organised around growth, objects, and driving forward a constantly expanding economy as benchmarks of success and prosperity. But this growing consumption at all costs is at odds with our understanding of what our planet can support. How do we lower the environmental impact of economic activity? How do we redefine success and prosperity separate from GDP, which politicians and governments have focused on for decades? We speak with ecological economist Tim Jackson, Professor of Sustainable Development at the University of Surrey, Director of the Centre for the Understanding of Sustainable Propserity, and author of...
Now Playing: Radiolab

An Announcement from Radiolab