New Biocalcifying Marine Bacterial Strains Isolated from Calcareous Deposits and Immediate Surroundings

Marine bacterial biomineralisation by CaCO₃ precipitation provides natural limestone structures, like beachrocks and stromatolites. Calcareous deposits can also be abiotically formed in seawater at the surface of steel grids under cathodic polarisation. In this work, we showed that this mineral-rich alkaline environment harbours bacteria belonging to different genera able to induce CaCO₃ precipitation. We previously isolated 14 biocalcifying marine bacteria from electrochemically formed calcareous deposits and their immediate environment. By microscopy and µ-Raman spectroscopy, these bacterial strains were shown to produce calcite-type CaCO₃. Identification by 16S rDNA sequencing provided between 98.5 and 100% identity with genera Pseudoalteromonas, Pseudidiomarina, Epibacterium, Virgibacillus, Planococcus, and Bhargavaea. All 14 strains produced carbonic anhydrase, and six were urease positive. Both proteins are major enzymes involved in the biocalcification process. However, this does not preclude that one or more other metabolisms could also be involved in the process. In the presence of urea, Virgibacillus halodenitrificans CD6 exhibited the most efficient precipitation of CaCO₃. However, the urease pathway has the disadvantage of producing ammonia, a toxic molecule. We showed herein that different marine bacteria could induce CaCO₃ precipitation without urea. These bacteria could then be used for eco-friendly applications, e.g., the formation of bio-cements to strengthen dikes and delay coastal erosion.