CaCO₃ nucleation by cyanobacteria: laboratory evidence for a passive, surface‐induced mechanism

Abstract

Calcite nucleation on the surface of cyanobacteria of the Synechococcus leopoliensis strain PCC 7942 was investigated to assess the influence of photosynthetic uptake of inorganic carbon and active ion exchange processes across the cell membrane on the nucleation and precipitation mechanisms. We performed long-term precipitation experiments at a constant CO(2) level in ambient air by adding suspensions of previously washed cyanobacteria to solutions of NaHCO(3)/CaCl(2) which were supersaturated with respect to calcite. Induction times between 4 and 110 h were measured over a range of saturation states, Omega, between 8 and 4. The kinetics of CaCO(3) nucleation was compared between experiments: (i) with ongoing photosynthesis, (ii) with cells metabolizing but not undergoing photosynthetic uptake of inorganic carbon and (iii) in darkness without photosynthesis. No significant differences were observed between the three treatments. The results reveal that under low nutrient concentrations and permanent CO(2) supply, photosynthetic uptake of inorganic carbon predominantly uses CO(2) and consequently does not directly influence the nucleation process of CaCO(3) at the surface of S. leopoliensis. Furthermore, ion exchange processes did not affect the kinetics, indicating a passive nucleation process wherein the cell surface or extracellular polymers provided preferential sites for mineral nucleation. The catalyzing effect of the cyanobacteria on calcite nucleation was equivalent to a approximately 18% reduction in the specific interfacial free energy of the calcite nuclei. This result and the ubiquitous abundance of cyanobacteria suggest that this process may have an impact on local and global carbon cycling.

Carbonates in Skeleton-Poor Seas: New Insights From Cambrian and Ordovician Strata of Laurentia

“…Model results do not reveal any strong variation in calcium-ion abundance through the later Cambrian-Middle Ordovician interval of interest (e.g., Demicco et al, 2005). Regardless of changing seawater chemistry, when [Ca 2+ ] far exceeds [CO 3 22 ], Ca 2+ may saturate calcium-binding sites on organic templates long before carbonate-binding sites fill, resulting in strong [CO 3 22 ] control of precipitation kinetics (Obst et al, 2009). For these reasons, and because Ca 2+ is far more abundant than CO 3 22 in seawater, likely for the past 540 myr (e.g., Horita et al 2002) and perhaps much longer, the distribution of V values in later Cambrian and Ordovician seawater must have been controlled largely by changes in carbonate-ion abundances due to the addition or removal of CO 2 .…”

Carbon gas fluxes from a brown‐water and a clear‐water lake in the boreal zone during a summer with extreme rain events

“…The lake itself has a fairly high pH and alkalinity and an exceptionally numerous population of signal crayfish (Pacifastacus leniusculus Dana). Transformation of DIC to solid phase can also take place through CaCO 3 nucleation by picoplanktic cyanobacteria (Obst et al 2009), which thrive in Lake Ormajä rvi (Jasser and Arvola 2003).…”

Intracellular Ca-carbonate biomineralization is widespread in cyanobacteria

“…The resulting alkalinity is transferred outside the cells, which raises the external pH and thus induces CaCO 3 precipitation (13). Other authors have stressed the importance of cell-surface properties of some cyanobacteria for the nucleation of CaCO 3 minerals and did not observe notable effects of photosynthesis on CaCO 3 precipitation (14). In any case, precipitation of CaCO 3 by cyanobacteria has been invariably considered a noncontrolled and extracellular process.…”