Rational Control of Calcium Carbonate Precipitation by Engineered Escherichia coli

Ureolytic bacteria ( e.g., Sporosarcina pasteurii) can produce calcium carbonate (CaCO₃). Tailoring the size and shape of biogenic CaCO₃ may increase the range of useful applications for these crystals. However, wild type Sporosarcina pasteurii is difficult to genetically engineer, limiting control of the organism and its crystal precipitates. Therefore, we designed, constructed, and compared different urease operons and expression levels for CaCO₃ production in engineered Escherichia coli strains. We quantified urease expression and calcium uptake and characterized CaCO₃ crystal phase and morphology for 13 engineered strains. There was a weak relationship between urease expression and crystal size, suggesting that genes surrounding the urease gene cluster affect crystal size. However, when evaluating strains with a wider range of urease expression levels, there was a negative relationship between urease activity and polycrystal size (e.g., larger crystals with lower activity). The resulting range of crystal morphologies created by the rationally designed strains demonstrates the potential for controlling biogenic CaCO₃ precipitation.