The influence of Salt Concentration on the Precipitation of Magnesium Calcite and Calcium Dolomite by Halomonas Anticariensis

The influence of Salt Concentration on the Precipitation of Magnesium Calcite and Calcium Dolomite by Halomonas Anticariensis

This research focuses on the formation of Ca-Mg carbonates by Halomonas anticariensis in solid media at different salt concentration and incubation time, and discusses the possible role of metabolic activity, bacteria surfaces and carbonic anhydrase in precipitation. Mineral saturation indexes of the solutions indicate that inorganic precipitation of different carbonates is possible in all media used but their precipitation did not occur in sterile control experiments. On the other hand H. anticariensis produced different Ca-Mg carbonates depending on salt concentration and Mg+2/Ca+2 ratios, in spite of its weak carbonic anhydrase activity. Incubation time does not influence the nature of the precipitates. At low salinity H. anticariensis precipitates magnesium calcite. A Ca-Mg carbonate phase with very small particle size, high lattice distortion (strain) and lattice parameters similar to those of disordered kutnohorite is presented and this phase is here referred to as non-stoichiometric calcium- rich dolomite, formed at high salinity. These Calcium-rich dolomites are rarely present in most natural habitats because this phase is thermo dynamically 32 metastable and it is subsequently transformed into calcite and dolomite.