This study assessed the role of picocyanobacterial photosynthesis in the induction of calcite precipitation.
It aimed at establishing whether photosynthetic uptake of bicarbonate by Synechoccoccus
cells leads to calcite nucleation.
The precipitation of calcite was initiated by addition of previously washed cyanobacterial cells of Synechococcus
PCC 7942 to solutions of calcium carbonate at different saturation levels with respect to calcite. Precipitation experiments
were performed under controlled laboratory conditions in two set-ups: one in which photosynthesis was inhibited
using a herbicide called Diuron and the other one in which photosynthesis was taking place. During the experiments, a
pH meter monitored the pH and ion selective electrodes monitored concentrations of carbonate and calcium ions. The
morphology of the precipitated crystals was analysed using Scanning Electron Microscopy. When the kinetics of
calcium carbonate nucleation by the Synechococcus
cells were compared for the two sets of experiments, there were
very little differences. In fact, the induction times for precipitation reactions with photosynthesis were shorter due to
the uptake of carbon dioxide. It is therefore, concluded that photosynthesis does not directly influence the nucleation
of calcite at the surface of Synechococcus
cells with sufficient supply of carbon dioxide, i.e. cells took up carbon dioxide
and not bicarbonate. The microscopic observations, however, provided some evidence that picocyanobacterial cell
walls act as a template for calcite nucleation.