Nav: Home

Symbionts as lifesavers

May 14, 2019

When people fall ill from bacterial infection, the first priority is to treat the disease. But where do these pathogens come from and how do they thrive in the environment before the infection occurs? An international team led by Matthias Horn from the Centre for Microbiology and Environmental Systems Science at the University of Vienna has tackled this question using an important bacterial pathogen that causes lung disease. The results of their study have been published recently in the scientific journal mBio.

Legionella pneumophila is the causative agent of Legionnaire's disease (legionellosis), an atypical pneumonia that is harmless for healthy individuals but can be life-threatening for immunocompromised patients. The number of cases of disease caused by Legionella has been on the rise worldwide since 2000, with 228 registered cases and 10 deaths in Austria in 2017 alone. The latest major outbreak in Europe occurred in the Italian city of Brescia in September 2018. More than 400 patients suffered from pneumonia and had to be treated in hospitals.

The natural habitat of Legionella are sediments from lakes and rivers, but they also occur in man-made water systems. "They multiply within protozoa such as amoebae, which are ultimately destroyed upon release of the pathogens. It is precisely this property that allows Legionella to infect humans. The disease usually only occurs after Legionella has proliferated in protozoa," explains Matthias Horn from the newly founded Centre for Microbiology and Environmental Systems Science, who together with his team and scientists from the Institut Pasteur and the University of Michigan has investigated the life cycle of Legionella in amoebae.

Protection against pathogens

Legionella are not the only bacteria able to survive in protozoa. Single-celled microeukaryotes such as protozoa often harbor other bacteria that do not harm them, so-called endosymbionts. The team of researchers has now discovered that these bacteria significantly influence the proliferation and spread of Legionella. In numerous experiments, they were able to prove that Legionella can proliferate less efficiently in amoebae if they contain endosymbionts. Surprisingly, most amoebae with endosymbionts survive the otherwise lethal infection with Legionella. "Those bacteria that had previously proliferated in amoebae with endosymbionts were considerably less infectious and were therefore less successful in infecting new amoebae" said Lena König, first author of the study and doctoral student at the Centre for Microbiology and Environmental Systems Science.

Uncovering the molecular mechanism

To better understand what happens inside amoebae which harbor endosymbionts and are infected by Legionella, the scientists took a closer look at the gene expression of both bacteria. "RNA sequencing allows conclusions to be drawn about biological events that take place within amoebae," explains Cecilia Wentrup, a postdoctoral researcher who played a major role in the project. König adds: "We found an explanation for the weakened infectivity of Legionella. They seem to lose the competition for nutrients inside the protozoa, which both the pathogen and the natural endosymbiont need to survive". The consequence: Legionella multiply more slowly and cannot produce virulence factors necessary for the infection of amoeba and humans. For example, the pathogen fails to become mobile and lacks important storage compounds.

From the laboratory to the environment

Yet another observation caught the interest of the researchers. The growth arrest did not only work with commonly used laboratory strains, but also with amoebae freshly extracted from the environment, as well as with recently isolated Legionella. Endosymbionts of amoebae are therefore a decisive factor for the proliferation and spread of Legionella not only under laboratory conditions, but probably also in the environment. This is particularly important because most amoebae carry bacterial symbionts under natural conditions. The current study thus contributes significantly to better understand the lifestyle of these bacterial pathogens in the environment.
The project was carried out at the University of Vienna as part of the FWF project "Eukaryotic genes in vacuolar pathogens and symbionts (EUGENPATH)" and a Marie Sk?odowska Curie Individual Fellowship Fellowship.

Publication in mBio:

Lena König, Cecilia Wentrup, Frederik Schulz, Florian Wascher, Sarah Escola, Michele S. Swanson, Carmen Buchrieser, Matthias Horn. 2019. Symbiont-mediated defense against Legionella pneumophila in amoebae.


University of Vienna

Related Bacteria Articles:

Conducting shell for bacteria
Under anaerobic conditions, certain bacteria can produce electricity. This behavior can be exploited in microbial fuel cells, with a special focus on wastewater treatment schemes.
Controlling bacteria's necessary evil
Until now, scientists have only had a murky understanding of how these relationships arise.
Bacteria take a deadly risk to survive
Bacteria need mutations -- changes in their DNA code -- to survive under difficult circumstances.
How bacteria hunt other bacteria
A bacterial species that hunts other bacteria has attracted interest as a potential antibiotic, but exactly how this predator tracks down its prey has not been clear.
Chlamydia: How bacteria take over control
To survive in human cells, chlamydiae have a lot of tricks in store.
More Bacteria News and Bacteria Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Teaching For Better Humans
More than test scores or good grades — what do kids need to prepare them for the future? This hour, guest host Manoush Zomorodi and TED speakers explore how to help children grow into better humans, in and out of the classroom. Guests include educators Olympia Della Flora and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#535 Superior
Apologies for the delay getting this week's episode out! A technical glitch slowed us down, but all is once again well. This week, we look at the often troubling intertwining of science and race: its long history, its ability to persist even during periods of disrepute, and the current forms it takes as it resurfaces, leveraging the internet and nationalism to buoy itself. We speak with Angela Saini, independent journalist and author of the new book "Superior: The Return of Race Science", about where race science went and how it's coming back.