Mutant bacteria accidentally recreated one of Van Gogh’s most iconic paintings

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The border between art and science is sometimes sinuous. Researchers studying a social bacterium that move and feed in coordinated swarms have unwittingly recreated something that looks a lot like a familiar masterpiece.

When a certain gene is overexpressed in a bacteria known as Myxococcus xanthus, individual organisms self-organize into tiny circular swarms within hours.

Once the resulting swarms are artificially colored, the scene looks remarkably similar to Van Gogh’s. The starry Night.

(D. Wall / University of Wyoming)

Above: A mixture of two strains of myxobacteria, one that overexpresses TraAB (yellow) and another that is non-sticky and non-reversible (blue) at 10x magnification.

“Our work highlights how a social bacterium, known for its rich sources of natural therapeutic products and as crop biocontrol agents, serves as a powerful model for studying emerging behaviors that also exhibit artistic beauty,” says microbiologist Daniel Wall from the University of Wyoming.

The starry Night. (Vincent van Gogh / Wikimedia Commons / Public domain)

Bacteria have a reputation for being selfish, but M. xanthus is described as a social bacterium because it needs to find and recognize relatives in order to survive.

After forming large family clumps, this rod-shaped bacterium is much better at attacking its prey for food. Each cell produces digestive enzymes that aid in feeding predators.

Researchers have been fascinated by this social behavior for years now, but we still don’t have a complete and widely accepted model for their complex movements.

In 2017, Wall and his colleagues announced the discovery of a single genetic “switch” responsible for turning this grouping behavior on and off.

The switch specifically controls a protein sequence, known as TraA, which provides a surface receptor for the bacteria to recognize and bind to the partner receptor, TraB, on its family.

Once bonded to a family member via these two receptors (TraAB), the bacteria can then exchange nutrients and proteins with the rest of the group.

When the swarm encounters food, laboratory research shows that organisms can actually pool their enzymes and metabolites through these connections to deliver the most powerful blow to their prey.

But that all changed when the team induced mutant bacteria to overexpress TraAB connections. This connection is what keeps cells together, but when there is too much of this “social glue,” the swarm cannot come apart as easily to change shape or direction.

Myxobacteria of a strain that overexpresses TraAB (green) and of a non-stick, non-reversible strain (red) at x4 magnification.  (Wall / University of Wyoming)(Wall / University of Wyoming)

Above: Myxobacteria from a strain that overexpresses TraAB (green) and a non-stick, non-reversible strain (red) at x4 magnification.

“In normal wild-type cells, they come and go, like a commuter train,” says bioengineer Oleg Igoshin of Rice University.

“The head becomes the tail and the tail becomes the head. And they do that every 8 minutes or so.”

Overexpression of TraAB, however, appears to prevent the swarm from tilting its head towards its tail and vice versa.

This is what computer models suggested to happen, but the authors still couldn’t figure out why. As far as they knew, the TraAB connection was not directly involved in regulating the swarm’s movements, only its adhesion.

Ultimately, the team suspected that TraB’s sticky quality was indirectly preventing the cell swarm from changing direction.

“Maybe our idea was that there is some kind of contact-dependent signal between cells that suppresses inversions,” says Igoshin.

“The cells are in dense groups and are in contact with others all the time, but these contacts are transient. But if the overexpression of TraAB makes you really sticky, your neighbor will stay your neighbor longer, and this could trigger the signal. which removes rollovers. “

1215 STAR D 775 full(D. Wall / University of Wyoming)

Above: Two strains of myxobacteria that overexpress different types of TraA receptors (red and green) that adhere to themselves but not to each other.

By performing this scenario in computer models, the authors were able to verify their intuition. With only modifications to the TraAB connection, the usual head-to-tail swarms suddenly became vortices of rotating cells, as large as a millimeter or more.

Further laboratory experiments then confirmed that this had also happened to bacteria in real life. Specifically, vortices can occur when a strain overexpresses stickiness, but also when a strain is genetically modified to be directly “non-reversible”.

The result is not only a better understanding of how millions of cells coordinate their movements, it is also a fascinating picture of the microbial world.

The study was published in mSystems.

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