More than meets the eye: how patterns appear in nature

Nature is full of patterns. Among them are tile patterns, which mimic what you would see on a tiled bathroom floor, characterized by both tiles and interfaces, like grout, in between. In the wild, the coloring of a giraffe is an example of a tiling pattern. But what causes these natural patterns to form?

A new study from the University of Arizona (UArizona) uses bacteria to understand how tiles and interfaces are created. The findings have implications for understanding how complex multicellular life may have evolved on Earth and how new biomaterials might be created from biological sources.

In many biological systems, tiling patterns are functionally important. For example, the wings of a fly have tiles and interfaces. Veins, which provide stability and contain nerves, are interfaces that divide a wing into smaller tiles. And the human retina at the back of the inner eye contains cells that are also arranged like a mosaic of tiles to process what’s in our field of vision.

Much research has examined how such patterns can be established through biochemical interactions. However, patterns can also be established by mechanical interactions. This process is not as well understood.

A new article published in Nature sheds new light on the formation of mechanical patterns. It was led by Honesty Kim, a former UArizona postdoctoral fellow. Ingmar Riedel-Kruse, associate professor in the Department of Molecular and Cellular Biology at UArizona, is the lead author of the paper.

The Riedel-Kruse lab, in partnership with researchers from the Massachusetts Institute of Technology’s Department of Applied Mathematics, used bacteria to model how tiling patterns can appear through mechanical interactions.

The team developed various adhesive, or sticky, molecules that were placed on the surface of bacterial cells, allowing different cell types to selectively stick together. When these altered bacteria were then placed on a Petri dish, the bacteria began to grow towards each other. Whenever two different bacterial types met, an interface formed or not, depending on whether their surface adhesion molecules were complementary or not. The interfaces were typically half a millimeter wide and 3 to 10 millimeters long, containing millions of bacteria. Many such interfaces then resulted in a variety of complex tiling patterns, depending on the initial bacterial locations on the petri dish.

The authors then investigated what kinds of tiling patterns could be generated and whether there is any underlying logic. They discovered that just four different adhesive molecules were enough to create any possible tile pattern. Mosaic patterns may vary in shape, size, and position of interfaces.

“We proved this mathematically with the famous four-color map theorem, which states that no more than four colors are needed to ensure that two countries touching each other on a political map do not have the same color,” Riedel-Kruse said.

The researchers thus generated many different models, including one that used interfaces to spell “U of A” for the University of Arizona.

The ideas proposed by the document can ultimately lead to practical applications.

Scientists could create patterned biomaterials with desired properties. For example, they could create a material with a specific pattern that could control how easily liquid flows over a material’s surface. Biomaterials are made from living things and could degrade faster than synthetic materials such as plastic.

“Using the logic of this research, shape, structure, elasticity and even how the fluid reacts – penetrating the material or repelling – can be controlled,” Riedel-Kruse said. “Or consider microbial biofactories to produce drugs and other chemicals. We could control where different bacteria are placed relative to each other to perform different parts of a complex reaction.”

The fact that only four adhesions are needed to create virtually every possible tiling pattern also offers new insights into how complex multicellular life might have evolved on Earth from single-celled life.

“The finding that four different adhesions are all it takes to create highly diverse mosaic patterns of life suggests that once enough adhesive components are available, developmental biology could generate many new forms,” Riedel said. – Kruse.

– This press release originally appeared on the University of Arizona website

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