Manifestations and environmental implications of microbially-induced calcium carbonate precipitation (MICP) by the cyanobacterium Dolichospermum flosaquae

The aim of this work is to explore the ability and magnitude of the temperate cyanobacterium Dolichospermum flosaquae in microbially-induced calcium carbonate precipitation (MICP). Environmentally, MICP controls the availability of calcium, carbon and phosphorus in freshwater lakes and simultaneously controls carbon exchange with the atmosphere. Cultures of flosaquae were grown in BG11 medium containing 0, 1, 1.5, 2 and 4 mg Ca2+ L−1, as cardinal concentrations previously reported in freshwater lakes, in addition to a control culture (BG11 containing 13 mg Ca2+ L−1). Growth (cell number, chlorophyll a, and protein content) of D. flosaquae was generally reduced by elevating calcium concentrations of the different salts used (chloride, acetate, or citrate). D. flosaquae exhibited its ability to perform MICP as carbonate alkalinity was sharply increased up to its highest level (six times that of the control) at a citrate concentration of 4 mg Ca2+ L−1. Calcium carbonate was formed at a pre-precipitation stage as the minimum pH necessary for precipitation (8.7) has been scarcely approached under such conditions. In this work, MICP took place mostly empowered by photosynthesis and respiration. Residual calcium exhibited its lowest value at 4 mg Ca2+ citrate L−1, coinciding with the highest alkalinity level. Precipitated calcium was increased with chlorophyll a content, but not with increasing cell numbers.