Petri dish with engineered E. coli forming Turing patterns (Photo: Ricard Solé)

Just before computer science pioneer Alan Turing’s untimely death in 1954, he devised a theory that continues to intrigue scientists more than half a century later. It mathematically answers the riddle of how complex, regular patterns — like the spots on a leopard or the stripes on a seashell — can arise from a simple, homogenous system.

These “Turing patterns,” and Turing’s proposed mechanism for generating them by an interacting “activator” and “inhibitor,” have been shown to occur in chemistry and physics. But their role in biology has been more difficult to prove experimentally. Now, a new study led by SFI External Professor Ricard Solé based at Universitat Pompeu Fabra and Salva Duran-Nebreda of the Institut de Biologia Evolutiva in Barcelona shows how a new class of Turing patterns work, using synthetic biology to create them from scratch in the lab.

“By using synthetic biology, we have a unique opportunity to interrogate biological structures and their generative potential,” Solé says. “Are the observed mechanisms found in nature to create patterns the only solutions to generate them, or are there alternatives?”

To find out, the team, which also included Jordi Pla, Blai Vidiella, Jordi Piñero, and Nuria Conde-Pueyo, began by considering potential mathematical models that could be implemented by engineering E. coli in the lab. Several attempts failed until the team found a design principle similar to mechanisms ants and termites use to build their nests. As the cells reproduced, the researchers observed how the growing colony evolved. Over a period of several days, as the cells continued to interact with one another, the shape of the circular colony began to change. As it expanded outward, it began to sprout “branches” around the perimeter, displaying regular spacing, just as Turing’s theory predicts.

The paper, published February 19 in the journal Synthetic Biology, offers “a new conceptual framework to create Turing-like patterns in microbial communities,” Solé says. Studying how these patterns emerge is key in understanding how complexity evolves in biology.

“The relevance of this study goes far beyond this specific implementation,” he says. “We suspect that hidden under the complexity of entangled gene interactions lies the kind of self-organization principles envisioned by Turing.”

The framework, which grew out of a collaboration between Solé and Duran-Nebreda at the Santa Fe Institute, can be applied to the study of other biological systems, such as social insects. Solé notes that the synthetic biology approach could also pave the way to studying how complex embryos develop from simple blastocysts, without having to resort to animal models.

Read the paper, “Synthetic Lateral Inhibition in Periodic Pattern Forming Microbial Colonies,” in Synthetic Biology (February 19, 2021)
 
Read the Universitat Pompeu Fabra press release
 
Read a 2009 paper on Turing patterns in seashells by the late SFI Science Board member George Oster, published in PNAS