Stork transmitter in the petri dish

Bacteria as conversation stoppers

Microorganisms not only use chemical signals to coordinate the behavior of their own colonies, they can also use them to disrupt the communication systems of other species.

Bacteria are relatively simple, yet they have developed astonishing abilities. For they are no speechless self-breadwinners, but quite communicative. Wherever there are large numbers of them, there is not only competition, but also cooperation and communication. And researchers are increasingly discovering the sophisticated mechanisms at work here.

The American researcher Bonnie Bassler is one of the pioneers in this field. More than ten years ago, they discovered that bacteria can not only communicate within their own species, but also use "universally understood" vocabulary. In a recent paper in Nature, she reports that some species of microbes can manipulate "conversations" to confuse others with them.

It’s the mass that counts

For a long time, they were regarded as unsociable, as absolute loners, focused only on reproducing themselves. In the meantime, it is clear that even the smallest life forms have a social vein. By means of certain messenger substances, they exchange information with each other – even across species boundaries.

One of the most important techniques at their disposal is the so-called quorum sensing. It refers to the ability to determine how many bacteria of the same or a different species are present in the environment. To measure this, the microbes continuously emit chemical signal molecules, so-called autoinducers. If their concentration exceeds a threshold value – i.e. if a certain population density is reached – this triggers a chemical reaction: some marine-dwelling bacteria (e.g. Vibrio. B. Vibrio fischeri, Vibrio harveyi) start to glow blueish, others form a dense biofilm.

Tiny saboteurs

Given the possibilities opened up by quorum sensing, it is not surprising that some organisms seek to interfere with the communication systems of other species for their own benefit. The molecular biologist Bonnie L. Bassler and her team at Princeton University’s Howard Hughes Medical Institute have investigated this amption. In earlier experiments, they had already dealt with quorum sensing in bacteria such as Vibrio harveyi, Escherichia coli and Vibrio cholerae The researchers at the University of Freiburg have been working on the signaling molecule Al-2, which is produced by a large number of microorganisms and enables them to communicate across species.

During their experiments, Bassler and his colleagues brought E. coli-Bacteria with the marine luminescent bacterium Vibrio harveyi together – a mixture that never occurs in the wild. However, in both species, the Al-2 production of one bacterium was able to trigger the quorum sensing of the other bacterium. Still, the common vocabulary Al-2 doesn’t always guarantee that the right message will get through. For E. coli can both produce and consume Al-2. In experiments in which Basler E. coli Al-2 consume dear, went at Vibrio harveyi the light off. Similar, albeit less clear-cut, results were obtained in corresponding experiments with the cholera pathogen Vibrio cholerae from.

"The really crucial thing about this is the interference," Bassler comments. "Consuming the signal could be a mechanism by which one bacterial species prevents another species from measuring its own population density and depends on it to coordinate behavior."

Hope for new medical therapies

At least 50 different species communicate via the Al-2 autoinducer, including pathogens that trigger disease. They live within their host without harming it, only when they become too strong, they change their behavior. In the lungs of people with cystic fibrosis, for example, the decision is made to use microcommunication Pseudomonas aeruginosa by quorum sensing when virulence factors are released. With the help of this strategy, the bacteria presumably manage to trick the human immune system and remain undetected in the early stages of infection.

In the meantime, the pharmaceutical industry also has high hopes for the decoding of microbial communication: previously dangerous bacteria could lose their pathogenic properties by capping the communication system.

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