Harnessing microalgae for the biosynthesis of molecular crystals

Highly reflective biogenic crystals such as guanine have potential as biocompatible alternatives to toxic inorganic optical materials. However, controlling the structural and optical properties of these sparingly soluble crystals in vitro is challenging. Engineered microbial cells have been used widely to generate high-value metabolites, but the biosynthesis of functional crystalline materials has not been achieved. Here we harness microalgae for the biosynthesis of difficult-to-crystallize molecular materials. We show that dinoflagellates can rapidly accumulate many nitrogen heterocycles from aqueous solutions into nitrogen-storage crystals, revealing a general mechanism for their metabolism of dissolved organic nitrogen. We manipulate this innate crystallization behavior to generate crystals with tailored morphologies and optical properties, including birefringent xanthine spherulites-a biogenic analog of TiO₂ nanoparticles. Our results show how microalgae may be exploited as cellular factories for producing molecular crystals from aqueous solutions, under ambient conditions, harnessing the intrinsic control mechanisms of crystal-forming cells, with possible further applications in the crystallization of pharmaceuticals and bioremediation of toxicants.