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

Abstract

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°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).

Keywords:

• biogenic carbonates
• biomineralization
• pedogenic carbonates
• calcifying bacteria
• soil bacteria

Acknowledgments

We thank L. Gianiorio for her assistance during laboratory work, LARIAN laboratory (Italian Center of Agricultural Consulting) for assistance in chemical-physical analyses of the soils, M. Giammatteo and L. Arrizza for assistance with SEM, G. Cappuccio for his collaboration in crystal XRD-analyses. We also thank G. Ferrini for the selection of the three different locations for appropriate sampling and C. De Rose and M. Roma for graphic and geographical assistance.