Figure 2.

Schematic diagrams of biologically controlled and induced mineralization (BCM and BIM). In BCM, anions and cations are taken up through transmembrane proteins into the cell. Through genetically controlled biochemical processes, minerals reach supersaturation and precipitate inside a membrane, despite extracellular undersaturation. In BIM, minerals of relatively non-uniform size and low chemical purity form via three possible pathways: (1) anionic species of extracellular polymeric substances (EPSs) bind with cations to nucleate mineral formation; (2) anions on the cell surface serve a similar function to nucleate mineral formation; (3) anionic species are excreted to outside the cell to bind with cations to precipitate minerals.