Aerobic microbial dolomite at the nanometer scale: Implications for the geologic record

Microbial experiments are the only proven approach to produce experimental dolomite under Earth's surface conditions. Although microbial metabolisms are known to induce dolomite precipitation by favoring dolomite growth kinetics, the involvement of microbes in the dolomite nucleation process is poorly understood. In particular, the nucleation of microbially mediated dolomite remains a matter for investigation because the metabolic diversity involved in this process has not been fully explored. Herein we demonstrate that Halomonas meridiana and Virgibacillus marismortui, two moderately halophilic aerobic bacteria, mediate primary precipitation of dolomite at low temperatures (25, 35 °C). This report emphasizes the biomineralogical implications for dolomite formation at the nanometer scale. We describe nucleation of dolomite on nanoglobules in intimate association with the bacterial cell surface. A combination of both laboratory culture experiments and natural samples reveals that these nanoglobule structures may be: (1) the initial step for dolomite nucleation, (2) preserved in the geologic record, and (3) used as microbial tracers through time and/or as a proxy for ancient microbial dolomite, as well as other carbonate minerals.