Biosynthesis of CACO₃ Crystals of complex morphology using a fungus and an actinomycete

The biosynthesis of CaCO₃ by reaction of aqueous Ca²⁺ ions with a fungus, Fusarium sp., and an actinomycete, Rhodococcus sp. (both plant organisms), is described. In the case of the fungus, cruciform-shaped calcite crystals are obtained (SEM picture A) while the actinomycete yielded the unstable polymorph of CaCO₃, vaterite (SEM picture B). Specific proteins secreted by the microorganisms are responsible for the morphology and crystallography control observed. A highlight of this approach is that the microorganisms also provide CO₂ for reaction with the Ca²⁺ ions, making the crystals completely biogenic.