Evidences for Bioprecipitation of Pedogenic Calcite by Calcifying Bacteria from Three Different Soils of L'Aquila Basin (Abruzzi, Central Italy)

To provide further evidences on the role of bacterial soil species in the development of calcium carbonate deposits in soil, we isolated 36 heterotrophic bacterial strains from three soils of L'Aquila basin characterized by different CaCO3 content and tested their ability to precipitate CaCO3 when cultured on a Ca-rich medium. We found that the majority (63.89%) of these isolates could precipitate CaCO3 minerals at 27 degrees C. The aptitude to calcification (time and crystal amount) of each calcifying strains, morphology (SEM) and mineralogy of the formed bioliths were also investigated. X-ray diffraction confirmed the production of calcite. Crystal formation was not observed in the controls. Organic matter, total N and assimilable P, cation exchange capacity and exchangeable Ca2+, Mg2+, K+, Na+, pH, total and active calcium carbonate content, electric conductivity, skeleton, sand, silt and clay fractions of each soil sample were determined and related with its microbiological parameters. We found that the CaCO3 content of soil was significatively related, in particular, to the percentage of calcifying bacterial strains (r = 0.95) and to the heterotrophic bacterial density (r = 0.98), which was found significatively related also with Ca2+ content of soil (r = -0.97) and its CEC (r = -0.97).