Calcareous deposit formation under cathodic polarization and marine biocalcifying bacterial activity.

CaCO3 precipitation can occur through bacterial activity (biomineralization) but can also take place in abiotic conditions in seawater at a steel surface under cathodic polarization. In this work, we used two biocalcifying bacterial strains: Pseudoalteromonas sp. and Virgibacillus halodenitrificans isolated in a previous work from marine environment for their ability to induce CaCO3 precipitation. Motility experiments were performed to evaluate the bacterial behaviour in the absence or presence of an applied electric current of -600 µA/cm2 in a solid medium. As no alteration of bacterial growth or CaCO3 crystal formation were observed, we studied both strains in liquid cultures at different applied currents densities: -100, -200 and -600 µA/cm2. The deposits formed on the cathode surface were characterized by µ-Raman spectroscopy and X-ray diffraction. The strain ability to biocalcify in the presence of electric current, in the liquid medium, was evaluated by monitoring bacterial growth, pH evolution, CaCO3 production and metabolic characterization for 7 days. Our results show that neither bacterial growth, enzymatic pathways or CaCO3 production were altered by the electric current. Moreover, bacterial activity modified drastically the nature of the compounds formed on the cathode surface. It favoured Mg-containing calcite, hindering the formation of both aragonite and brucite.