STUDY OF BIOMINERAL FORMATION BY BACTERIA FROM SOIL SOLUTION EQUILIBRIA

The role of bacteria in mineral neoformation in a saline soil was stud ied. In this soil, authigenic precipitation of gypsum and calcite take s place. Bacteria isolated from the soil were cultivated 'in vitro' in solid and liquid media prepared from soil solutions (1:1 extract). Pr ecipitation of calcite spherulites of between 20 and 50 mu m diameter and of other bioliths was observed. From soil solutions (1 : 1 extract and saturation extract) activity coefficients and the states of react ion for 18 minerals were calculated using the SOLMINEQ 88 program. Cal cite, dolomite, gypsum and aragonite were in equilibrium with the satu ration extract while in the 1 : 1 extract no mineral phases in equilib rium were present. Therefore, bacteria must play an active role in cal cite precipitation in this saline soil. (C) 1998 Elsevier Science B.V. All rights reserved.