Precipitation of carbonates by bacteria from a saline soil, in natural and artificial soil extracts

The precipitation of carbonates by populations of bacteria from a saline soil cultivated in both solid and liquid culture media was studied. The soil was a Gley- Gypsic- Carbonated Solonchak from near an inland saltern in Granada, Spain. Two types of soil extract were prepared: 1: 1 extract and saturation extract. The soil samples used for the bacteriological analysis were taken in situ from the A and C soil horizons. The culture media were made from ( 1) soil extract, ( 2) artificial soil solutions, and ( 3) artificial solutions of marine salts. The geochemical analysis of the solution was carried out using the program PHREEQC. Samples of purified bioliths were examined by X- ray diffraction and were observed with SEM. We found that the mineral precipitated from the natural and artificial soil extracts was calcite. Calcite was also found in the secondary accumulations of this soil. However in the media derived from marine salts, mixtures of calcite, magnesian calcite, and aragonite were precipitated, depending on the Mg2+ concentration, the [ Mg]/[ Ca] molar ratio, and the type of medium. The morphology of the minerals precipitated shows bacterial involvement in the process of pedogenic bioprecipitation. The precipitation studied could be regarded as a process of induced biomineralization.