The line between art and science can be swirling. Researchers studying social bacteria that move and feed collaborative herds have unintentionally recreated something very similar to a familiar masterpiece.
When a gene is overexpressed in bacteria Myxococcus xanthusWithin hours, individual organisms self-organize into small circular herds.
The scene is very similar to Van Gogh’s scene when the resulting herd is artificially colored. Starry night..
Above: A mixture of two strains of myxobacteria. One is overexpressing TraAB (yellow) and the other is non-adhesive and non-reversing (blue) at 10x magnification.
“Our work is as a powerful model for studying emergency behavior, which is known as a rich source of therapeutic natural products and bio-controlling agents for crops, which also exhibits artistic beauty. We emphasize how it helps, “says Daniel Wall, a microbiologist at the University of Wyoming.
Bacteria have a reputation for being selfish, M. xanthus It is described as a social bacterium because it requires finding and recognizing relatives in order to survive.
After forming a large familial mass, this rod-shaped bacterium is much better at attacking and feeding prey. Each cell produces a digestive enzyme that promotes predatory feeding.
Researchers have been fascinated by this social behavior for years, but we still do not have a comprehensive and widely accepted model for their complex movements.
In 2017, Wall and his colleagues announced the discovery of a single gene “switch” that turns this grouping action on and off.
This switch specifically controls the protein sequence known as TraA. It provides a surface receptor for the bacterium to recognize and attach to its relative’s partner receptor, TraB.
Adhesion to family members via these two receptors (TraAB) allows bacteria to exchange nutrients and proteins with other members of the group.
When a herd encounters food, laboratory studies show that the organism can actually pool enzymes and metabolites together through these connections, giving the prey the most powerful punch.
But when the team overexpresses the TraAB connection in the mutant bacterium, it all changes. This connection allows cells to stick together in the first place, but if there is too much of this “social glue”, the flock can easily break and become unable to change shape or direction.
Above: Myxobacteria from strains that overexpress TraAB (green) and non-adhesive and non-reversing (red) strains at 4x magnification.
“Normal wild-type cells move back and forth like a commuter train,” explains Oleg Igosin, a bioengineer at Rice University.
“Heads become tails, tails become heads, and they do it every eight minutes or so.”
However, overexpression of TraAB appears to prevent the herd from switching head-to-tail and vice versa.
This was suggested by the computational model, but the author still couldn’t understand why. As far as they know, the TraAB connection was not directly involved in the regulation of herd movement, but only in its stickiness.
Ultimately, the team suspected that TraB’s stickiness indirectly prevented the change of direction of the cell herd.
“Our idea may have been that there was some contact-dependent signal between the cells that suppressed the reversal,” explains Igoshin.
“The cells are in a dense group and are always in contact with other cells, but those contacts are temporary. But if overexpression of TraAB really makes you sticky, your neighbors Reversal that remains your neighbor and it can cause a signal to suppress. “
Above: Two myxobacterial strains that overexpress different types of TraA receptors (red and green) that do not adhere to each other but adhere to each other.
By running this scenario in a computational model, the authors were able to verify their intuition. By simply changing the TraAB connection, the normal head-to-tail swarm suddenly became a rotating swirl of cells larger than 1 millimeter in size.
Further experiments in the laboratory then confirmed that this also happened to real-life bacteria. Specifically, swirl can occur not only when the strain overexpresses stickiness, but also when the strain is genetically modified to be directly “non-reversed”.
The result is not only a better understanding of how millions of cells regulate movement, but also a fascinating picture of the microbial world.
The study was published in mSystems..