The recipe of nature is old, has evolved more than once

In recent years, scientists have unveiled many of the secrets of biomineralization, the process by which sea urchins grow, molluscs build their shells and corals make skeletons, and how mammals and other animals make bones. and teeth.

The materials animals make from scratch to build protective shells, sharp teeth, bones and needle-like spines are some of the hardest and most durable substances available. The recipe for making these materials was one of Nature's well-kept secrets, but new analytical tools and powerful microscopes solved much of the mystery, showing the scale nanoscale how a large number of animals use exactly the same mechanisms and the same starting chemicals. to manufacture the biomineral structures on which they depend.

Now, in a report released today (August 19, 2019) in the Proceedings of the National Academy of Sciences (PNAS), a team led by Pupa Gilbert, professor of physics at the University of Wisconsin – Madison, shows that the recipe for making shells, spines and coral skeletons is not only the same, in many bloodlines. Modern animals, but that it is millions of years old – and have evolved independently more than once.

The results are important because they help assemble an evolving story of biomineralization. The more complete picture of an ubiquitous process in animal life on our planet tells us not only something important about our world, but the details may one day be exploited by the human to produce harder, lighter and more durable materials; tools that never need to be sharpened; more faithful biomedical implants; and the possibility of human intervention in areas such as the reconstruction of the world's coral reefs.

"The discovery that biomineralization has evolved independently several times, using the same mechanism, tells us that there is a strong physical or chemical reason for doing so," says Gilbert, a global expert on the process of biomineralization . "If an organism starts making its biomineral this way, it outperforms all the others who do not do it or differently, it's not eaten and has to convey that good idea throughout the lineage."

New PNAS The report draws on a series of major discoveries by Gilbert and his colleagues. In previous studies, the Wisconsin physicist has shown that the biomineralization process works the same way in very different animal classes, ranging from molluscs such as abalone to echinoderms such as sea urchins. and cnidaria, a large group of animals including corals. jellyfish and sea anemones. These phyla, or large groups of animals, do not have a common ancestor that was already biomineralising. They must therefore have developed biomineralization mechanisms independently. Therefore, says Gilbert, "it is extremely surprising that, when they started the Cambrian biomineralization (more than 500 million years ago), these three phyla began to do exactly that. same way: using the attachment of amorphous nanoparticles ".

"Biomineralization exemplifies both the unity and diversity of nature," says Andrew Knoll, professor of natural history and Earth and planet sciences at Harvard University, and co-author of the new report . "The biomineralized skeletons may have evolved up to twenty times in animals only, which means that none of these biomineralising groups share a common ancestor that has itself shaped a biomineralized skeleton."

Gilbert and his colleagues have shown that different biominerals are formed from amorphous calcium carbonate nanoparticles, which are produced in cells and are the essential starting chemical for all the materials that form in the process of biomineralization, which 39 it is mother-of-pearl or the mother of the mother. pearl, which lines an abalone shell or the teeth of a sea urchin grinding rocks. "More of a biomineral is being formed with these amorphous precursor nanoparticles," Gilbert said. "It does not matter that it's like a sea urchin spike, a tooth, a spine, a mother-of-pearl or a mother-of-pearl." a coral All these systems have the same amorphous precursors.

"The amorphous calcium carbonate nanoparticles," adds Gilbert, "are stabilized in a confinement and in a reversible way, so the crystals do not nucleate and grow in the right place at the right time, but they can and do make it to the right place and at the right time, that is, on the growing surface of a shell, a coral skeleton, a sea urchin spine. "

The ability of many animals to make hard, protective or defensive structures, Knoll says, was probably a general response to the evolution of carnivores, resulting in a "biomineralization surge" observed in the fossils of the Cambrian period. about 541 million years ago. .

The microscopic particles of calcium carbonate produced in animal cells are the same material that forms "lime" deposits in pipes and plumbing fixtures. In an animal, it is transformed at the site of biomineralization by binding to the site and forming crystals in which individual atoms are perfectly aligned to form a network, a scaffolding of the kind, whatever the structure that is in place. an animal is building. The process was developed by Gilbert's team using a new microscope that uses the soft x-rays produced by synchrotron radiation to observe at nanometer scale the approximation of structures as and when their training.

Gilbert's team has stepped back in time by applying the same techniques to probe deep fossils in three distinct phyla, or large groups of related animals, dating back up to 550 million years ago. to sample the oldest known animal biomineral: the Cloudina skeleton with its characteristics. series of funnels nestled into each other.

Gilbert notes that, although animal remains undergo significant changes in the fossilization process, the biomineralization signature of nanoparticles remains intact and is observed by cracking open fossils and using a scanning electron microscope to probe the site of the fracture to detect the warning signs of nanoparticles during the initial period. crystallization process. "We have retreated as much as possible in the past, up to the first fossils, and biomineralization by particle fixation has the same appearance as in modern animals."

The history of biomineralization reported by Gilbert and his colleagues could inform the development of new materials useful for the industry.

"We do not know how to ensure that amorphous calcium carbonate or any other material forms a solid filling the space then crystallizes, but the cells of marine organisms know it," says Gilbert. "What we learn from them, we can reproduce in the lab and in the industry, and make much better materials than the sum of their components, as are all biominer."