Swirling bacteria mimic Van Gogh's 'The Starry Night'

Two myxobacteria strains that have different types of TraA receptors that adhere to themselves, but not each other, have been combined in an experiment. D. Wall is from the University of Wyoming.

Scientists have discovered a way to transform predatory millions ofbacteria into swirling flash mobs reminiscent of painterVincent Van Gogh's "The Starry Night" as the unexpected result of experiments on a genetic circuit the creatures use to discern friend from foe.

Myxococcus xanthus has been studied for decades as a model system for social cooperation. Researchers from Rice University and the University of Wyoming discovered a previously unreported behavior while studying M. xanthus mutants that overexpress two proteins.

An image from the study will be featured in a forthcoming issue of the open-access journal, and the research is described in a study published online in the American Society for Microbiology's mSystems.

"When you overexpress that protein, you can see these circular aggregates emerge after four hours, and by 12 hours they take up the whole (petri dish)," said study co-author Oleg Igoshin, a professor of bioengineering at Rice and senior scientist at Rice's Center
Igoshin's research group and the Wyoming microbiology group collaborated for five years on the study, conducting dozens of laboratory and computational experiments to uncover the genetic mechanism of the circular swarms.

M. xanthus preys on otherbacteria. Lacking internal organs to digest their prey, they band together in family packs to devour victims, which can include M. xanthus that aren't members of the family.

A strain of myxobacteria that overexpresses TraAB and is non-adhesive and non-reversing is depicted at four times magnification. D. Wall is from the University of Wyoming.

Five years ago, Wall and his graduate student, Pengbo Cao, showed that M. xanthus uses a surface receptor called TraA and a partnerprotein called TraB to recognize kin. The TraAB complex acts as a kind of glue when M. xanthus bumps into a close relative. TraAB helps poison non-kin when M. xanthus runs into unrelated M.

While investigating the mechanism of TraAB, Wall's team created several strains, including some that overexpressed TraAB, making more of theprotein than normal, and they formed within a few hours. Igoshin's group was asked if it could create a theoretical model that could explain the mystery.

Igoshin said that the only way to see the circular aggregates in simulations is to make the cells non-reversing. They go back and forth, like a commuter train, in normal wild-type cells. The head and tail are the same thing. They do it every eight minutes.

The model was developed by Igoshin and his graduate students and used changes to TraAB and other signaling circuits to model M. xanthus behavior.

"Our first idea was that they're sticky and can't reverse," Igoshin said. We tried to see if sticky cells would form circular aggregates. Nothing happened after we added a very strong adhesion to our simulations. They did not make circles. The simulations worked if we instead stopped the reversals. Aggregates emerged.

Cells in the aggregates did not reverse, but that raised more questions.

A strain of myxobacteria that overexpresses TraAB and a strain that is non-adhesive and non-reversing are both shown in the image. D. Wall is from the University of Wyoming.

Igoshin said that TraAB overexpression in aggregates prevented cells from reversing. This was cool for us because our model predicted it. This was a bit puzzling and completely unforeseen. TraAB didn't have anything to do with reversal regulation.

There were a few possible explanations that were ruled out. There was evidence suggesting TraAB could be the key.

How is it that the reversals are suppressed? Igoshin said something. The idea was that there was a contact- dependent signal between the cells that suppressed the reversals. The cells are in contact with each other all the time, but they are not always in contact with each other. If TraAB overexpression makes you sticky, your neighbor will remain your neighbor for longer, and that could signal the reversals.

The model began to produce patterns that were very similar to what Wall's team was seeing. Igoshin's team wanted to see if the model could predict a behavior that hadn't been seen in experiments. They would form large rotating swarms with the two strains.

Wall's team applied false color to images of the colonies to reveal a song by M. xanthus.

"Our work shows how a social bacterium, known for rich sources of therapeutic natural products and as crop biocontrol agents, serves as a powerful model for studying emerging behaviors that also exhibit artistic beauty," Wall said.

Kalpana Subedib of the University of Wyoming is a co-author.

The Emergent Myxobacterial Behaviors Arise from Reversal Suppression Induced by Kin Contacts, mSystems is more information. There is a book titled "mSystems"

There are swirlingbacteria that mimic Van Gogh's 'The Starry Night'.

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