The Rapid Dolomite Formation Mediated By Microorganisms

Dolomite, which is the carbonate mineral composed of calcium andmagnesium carbonate, could be widely found in both terrestrial and marineenvironments. Besides, dolomite is commonly found in many petroleumreservoirs, thus the study on dolomite formation is helpful for resourcemining. It has been more than three hundred years since the discovery ofdolomite, but the origin of dolomite is yet unclear, referred as dolomiteproblem. In the1990’s, C. Vasconcelos from Swiss Institute ofTechnology promoted a model of microbial dolomite formation whichprovided a new perspective on the origin of dolomite. Until now thereported experiments on dolomite formation mediated by microorganismswere performed at ambient temperature and pressure, and only micronspindle， dumbbell or spherical crystals were observed, which weredistinguished from natural rhombohendral dolomite crystals. In thisresearch, we used different bacteria to mediate dolomite formation undervarious environmental conditions like temperature (15°C and30°C),pressures (ambient and20MPa) and oxygen concentrations (aerobic andmicro-aerobic). For the first time hydrostatic pressure was introduced as anadditional environmental parameter in combination with the physiologicalstatus of bacteria in order to investigate the dolomite formation undermultiple conditions. Four species of bacteria Lysinibacillus sphaericus、Sporosarcina psychrophila, Shewanella piezotolerans WP3and anunnamed Methylophaga strain were used as biomass to mediate dolomiteprecipitation. According to SEM and EDS results, Lysinibacillussphaericus and Sporosarcina psychrophila have been proven to be able tomediate irregular rhombohendral dolomite crystal due to their ureahydrolysis activity after four days under high hydrostatic pressure (20MPa) and temperatures (15°C and30°C). Besides dolomite, other minerals(such as calcite, nesquehonite and huntite) were detected spontaneously. Inthis case, urea hydrolysis activity, temperature and hydrostatic pressure allhave great influence on dolomite formation. Although Methylophaga is astrain isolated from cold seep, it failed to mediate dolomite formation dueto its acidity production. According to the SEM and XRD results,Shewanella piezotolerans WP3is able to mediate dolomite precipitation ina low amount under the condition of hydrostatic pressure. This studyindicated that various microorganisms were able to mediate dolomiteformation. Besides the environmental factors, the cellular status is also akey parameter influencing dolomite formation. This provided us a newperspective and more data to optimize the model of microbial dolomiteformation.