Shining light on how pearls and other biominerals are formed Finding answers between biochemistry and mineral chemistry

The process by which living organisms produce inorganic minerals is known as biomineralization, and the minerals produced by living organisms are called biominerals. Typical examples include pearls, shells, corallum (coral skeletons) and the exoskeletons of shrimp and crabs. In human beings, our bones, teeth, and stones that form in the urinary tract are similar examples. While these biominerals have extremely intricate structures and superlative material properties, it has not been clear how they are formed. Associate Professor Michio Suzuki has elucidated one aspect of this mechanism using the example of Akoya pearl oysters (Pinctada fucata), which are used in pearl aquaculture.

“Akoya pearl oyster shells can be divided up into a nacreous or mother-of-pearl layer that casts the same iridescent luster as the pearl, a prismatic layer outside that, and then the outer shell beyond that, along with the ligaments at the hinges. Chemical analysis of the intricate structure of the nacreous layer has revealed that a key role is played by a novel matrix protein known as Pif. That is, Pif interacts with the calcium carbonate crystals to control the nacre formation.”

This analysis would have been impossible to attempt without an understanding of both organic and inorganic matter. While these two tend to be conceptualized separately in the world of chemistry, for Suzuki, who specialized in biochemistry at the Graduate School of Agricultural and Life Sciences and mastered methods for analyzing inorganic minerals at the Graduate School of Science and in overseas laboratories, it was only natural to consider both.

“The year I spent at the Weizmann Institute of Science, a hub for the world’s top biomineral researchers in Israel, was inspiring. I was a postdoc when I returned to Japan, where I married one of my younger colleagues at the laboratory. At the time, I was living on one-year appointments, so I felt that I would never be able to get married if I waited for my career to stabilize.”

Suzuki says that with the elucidation of the mechanisms of biomineral production, “the players are finally ready to go.” Many unclear molecular mechanisms yet remain, and he is now at a stage where he can begin to proceed with full-scale research. If the whole mechanism can be understood, it will be possible to improve the efficiency of pearl farming, which currently entails significant waste. And we cannot overlook the soil improvement effects and antibacterial properties of the oyster shells. Moreover, the shells – which contain a lot of calcium carbonate – play a role in fixing atmospheric CO₂, which could potentially contribute to the prevention of global warming.

“Of course, I'm not necessarily doing research with the idea of helping in any one thing in particular. For me, ideally, the results of my devotion to basic research will lead to the creation of things that will be widely used in society.”

Once, Suzuki would spend most of his waking moments on experiments, but these days he enjoys playing with his three children in the park. Seven years ago, as one might expect, he chose a Mikimoto pearl for his wife’s engagement ring.