Selective dissolution of calcite in a bacterial habitat environment

It has been well known that the activity of bacteria causes a promoting crystallization in the natural environment. On the other hand, it has been pointed out that bacteria activity also plays a role in the dissolution of crystals, and the microscopic observation showed that the inhibition of the bacteria affects the pit formation to promote the dissolution of calcite[1]. The authors found a grope of bacteria, which promotes the dissolution process of calcite. We isolated bacteria from calcite-enriched soil and examined their calcite-degrading activity.To understand the role of bacteria in the dissolution process, In the experiments, the cleavage surface of the calcite was exposed to the culture fluid of the bacteria for 4 days to investigate the effect of bacteria on the calcite dissolution. The surface morphology of the calcite was investigated using an optical microscope and scanning electron microscope after the dissolution experiment in the culture fluid with bacteria.The calcium ion concentration in the culture fluid of Streptomyces was one-third of control, Escherichia coli DH5a, indicating the promoting the dissolution process of calcite. The surface observation of the calcite surface, which has been exposed in the culture fluid of bacteria shows the etch pits, which were formed during the dissolution process.Differing from the previous study, [1] the shape of the etch pits showed a rounded and asymmetric shape and deviated from the rectangular, which reflects the symmetry of the surface. These etch pits were formed accompanied by the bacteria colony. And the bacteria colony was formed along the cleavage step on the calcite surface. These observations infer that the inhabitation of the bacteria and the dissolution of the calcite are related to each other and the effect of the surface activity of calcite in the dissolution process could be larger by the biological activity.Reference[1] A. Luettge and P.G. Conrad, Direct observation of microbial inhibition of calcite dissolution, App. Env. Micr (70) 2004