BCC structures formed in non-coupled and coupled calcium-carbon sources. SEM images of BCC-GLC (a, c) and BCC-ACE (c, d) are shown. Scales (a) and rhombohedral calcite irregular shapes (c) are present. Crystallites grow over calcite aggregates and mineralized EPS in non-coupled sources (a, b). Besides, induced mineralization occurs over the cell wall in coupled source (d). Scale bars: 1 μm.