Effect of Escherichia coliform on the biomineralization of calcium bilirubinate in mimic systems

The influence of Escherichia coliform (E. coli), especially the proteins it secretes, on the nucleation, growth and aggregation processes of calcium bilirubinate (CaBR) in different mimic systems, such as NaCl aqueous solution and model bile, is studied in this paper. The results show that in NaCl aqueous solution the morphology of calcium bilirubinate (CaBR) changes from amorphous sheet structure to a highly self-organized and highly self-replicated fractal structure that is accumulated by rhombic microcrystals after the addition of E. coli. In model bile with the existence of E. coli, CaBR also forms a fractal structure, but the fractal structure is staghorn-like. Meanwhile, the composition of the prepared CaBRs is nonstoichiometric, and the crystallization is greatly improved with the existence of E. coli. Besides, formation mechanism of CaBRs affected by E. coli is explored, showing that the proteins secreted by E. coli interact with the Ca2+ ions to provide nucleation sites for CaBRs, and the conformation of the proteins becomes more ordered, resulting in the improvement of the crystalline of CaBRs. On the other hand, the interaction of proteins and the Ca2+ ions also promote the aggregation state of the CaBRs.