| Several bacterial species influence carbonate mineral precipitation by modifying pH, alkalinity, Ca2+ activity and by providing nucleation sites for mineralization. Two studies have been undertaken to explore microbial influence in the mineralization of carbonates. In the first study, the ability of sulfate-reducing bacteria (SRB) to induce carbonate mineralization was investigated as a means to enhance mineral sequestration of CO2. Sulfate-reducing bacteria enriched from hypersaline Storr's Lake, The Bahamas; Lake Estancia, New Mexico; and Great Salt Plains Lake, Oklahoma, were tested in reactors under varying CO2 concentrations. Carbonate mineral precipitation was achieved only in reactors with Lake Estancia SRB community and under a pCO2 of < 20 psi. Hydrogen, lactate and formate served as electron donors for SRB. Carbon isotopic studies confirmed that carbon in the carbonate minerals was derived from electron donors, CO 2 or bicarbonate ions in the solution. Sulfate-reducing bacteria's ability to induce immobile carbonate mineralization can be potentially applied to enhance long-term storage of CO2.;Secondly, microbially lithified, organo-sedimentary structures called microbialites in the hypersaline Storr's Lake were investigated to determine the influence of biotic and abiotic components of the lake on the microbialite formation. The lake water revealed fluctuations in several parameters depending upon rainfall and evaporation. Aragonite and Mg-calcite constituted the carbonate mineralogy of the five microbialites morphologic types examined. Microbial diversity studies by 16S rRNA gene analysis revealed high population percentages of anaerobic phototrophs, halo-respirers and sulfate-reducing bacteria and low population of cyanobacteria (3%). The fluctuating water characteristics, varied mineralogy and the low apparent abundance of cyanobacteria, makes Storr's Lake, a distinct environment to study microbial interaction with their surroundings during carbonate mineralization. |
