Fig. 4.

SEM photomicrographs of bacterial attachment and CaCO₃ biomineralization on calcite. a General overview of the calcite substrate subjected to bacterial biomineralization; b bacterial cells (bc) onto calcite 17 h after inoculation; c detail of bacterial cells and newly formed CaCO₃ (arrow); d initial calcification of bacterial cells that keep their rod-shaped morphology, whereas uncalcified cells (darker contrast) collapse during sample preparation (drying) and observation (high vacuum); e bright field (negative) SEM image taken with an STEM detector of bacterial calcite crystals formed after 24 h incubation time, one of them including an entombed bacterial cell (bc); f bacterially induced CaCO₃ crystals (Bcc) along with EPS and collapsed bacterial cells (EPS + bc) on the calcite substrate; g bacterial calcite structures formed on the calcite substrate during the early stages of biomineralization (24 h after inoculation). Rod-like bacterial cells are seen partially entombed in newly formed CaCO₃ (arrow); h calcite substrate fully covered by bacterial calcite after 48 h; i detail of the nanostructured bacterial calcium carbonate structures shown in h