Morphology of mineralization products. Morphological variations of the mineralized CaCO3 after 20 days in medium with and without Zn2+. A) In MH 2 medium triangular CaCO3 platelets were mineralized and assemble into globular agglomerates with equatorial constrictions. B) Cross sections of these agglomerates show the internal construction, which consists of two clearly distinct regions. A smooth inner region is surrounded by an outer region which is composed of triangular platelets and globular particles. The inner region might have been the localization site of bacteria that have been the starting point for particle agglomeration. C) In MH 2Z medium (with Zn2+) particles show a mixed structure of platelet (arrow 1) and sponge like structures (arrow 2). D) In MH 4 medium the initial globular inorganic particles on the bacterial cells elongated and form columnar structures. E) In addition to densely packed needle-like structures. F) In MH 4Z medium only irregular agglomerates consisting of columnar structures (arrow 1) and sheet like structures (arrow 2) are mineralized. Bars represent 1 μm.