Research on the biogenic-specific polymorphism and morphology of carbonate has been gaining momentum in the fields of biomineralization and industrial engineering in recent years. We report the nucleation of carbonate particles on bacterial cell templates to produce a novel dumbbell-like morphology which was assembled by needle-like crystals of magnesium calcite or aragonite radiating out from both ends of the template bacterium. Mature dumbbell-like structures had a tendency to break apart in the central template region, which was made up mostly of weak amorphous carbonate. Further crystal growth, especially at the template region, transformed the broken pieces into spherulites. Rod-like cell templates were essential for the formation of dumbbell-like morphologies, and we propose a possible formation mechanism of the dumbbell-like morphology. Our findings provide new perspectives on the morphological formation mechanism in biomineralization systems and may have a potential significance in assembling composite materials suitable for industrial applications.
