In this study, a method for the bacterial production of a nacre-mimicking composite material was developed. Nacre (mother-of-pearl) is an organic-inorganic composite found in the inner lining of many mollusk shells and in pearls. It has a brick-and-mortar structure consisting of 95% aragonite (calcium carbonate) platelets and 5% organic matrix. Serving as a protective structure against e.g. predators, nacre has developed into an extremely strong and tough material, despite largely consisting of ceramic calciumcarbonate. Numerous mechanisms have been proposed to explain the outstanding mechanical properties of nacre, such as crack deflection and local strain hardening. Many groups are pursuing the aim of developing new materials which mimic nacre’s structure and mechanical properties. Nacre is produced by mollusks at ambient temperatures with easily obtainable materials and with low expenditure of energy. In contrast, human methods usually require extensive energy input, high temperatures and/or pressures, and environmentally damaging chemicals.