Elemental analysis of bacteria cells and the mineralized inorganic phase by EDX spectroscopy. For both culture media calcium accumulated to high levels, reflecting the formation of calcium carbonate. In medium with zinc acetate supplementation (upper spectrum, + Zn2+) additional zinc peaks were detected compared to the one without zinc (− Zn2+). The detection of osmium and platinum is due to the subject of sample preparation and staining. The silicon peak originates form the silicon wafer which was used as sample holder.