Bio-precipitation of Calcite with Preferential Orientation Induced by Synechocystis sp. PCC6803

This article presents a research study on the deposition process of Ca²⁺ induced by Synechocystis sp. PCC6803 in BG11 liquid medium with different Ca²⁺ concentrations and different pH. The changes of Ca²⁺ concentrations were measured by using atomic absorption method and the corresponding dynamical models were studied. Minerals and cells were analyzed by high resolution transmission electron microscope, selected area electron diffraction, scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffraction. The selected area electron diffraction patterns were analyzed by Digital Micrograph 3.7 software. The result showed that Ca²⁺ concentrations decreased faster in the experimental group. The changes of calcium carbonate precipitation were fitting to an exponential model. PH 7 and Ca²⁺ concentration of 1.5 g/L were most conducive to calcium carbonate precipitation in the corresponding gradient range. The result of high-resolution transmission electron microscopy showed that minerals in the experimental group differed obviously from that of the control group in the surface morphology, but both of them were calcites. It also showed that a certain number of minute calcites adhesion to the outer surfaces of S. PCC6803 cells. The result of scanning electron microscopy displayed that many sunken holes emerged on the surfaces of the prismatic calcium carbonate minerals. The results of X-ray diffraction proved that minerals induced by S. PCC6803 were calcites with preferential orientation. This article discusses the process of carbonate formation and the possible role played by S. PCC6803. It may be useful to further study the mechanism of microbial carbonates deposition in the field of geology.