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From 2010.igem.org

Calcium Carbonate

Calcium carbonate precipitation is a widespread process among bacteria. The process are controlled by two distinct pathways, namely biologically induced pathway and the biologically controlled pathway. In the biologically controlled pathway, bacteria is able to control the precipitation of calcium carbonate and deposit it intracellularly. In contrast, in the biologically induced pathway, no specialized cell structure or specific molecular mechanism is thought to be involved. However environmential conditions were known to play a part.

A cluster of five genes (lcfA, ysiA, ysiB, etfB, and etfA) called the lcfA operon was involved in the calcium carbonate precipitation isn Bacillus subtilis.