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.