Figure 1.

Complex colony morphology correlates with calcite precipitation in Bacillus subtilis. (a–c) Top view of a colony of an undomesticated strain of wild-type B. subtilis (NCIB 3610). The colonies were grown on solid biomineralization-promoting medium without (a) or with (a and b) a calcium source, for 3 and 7 (a), 21 (b) days, at 30 °C, in a CO₂-enriched environment. (b) Top view of a colony (left) and a magnification of calcite crystals at the periphery (right upper) or centre (right lower) of the colony. Images were taken by Stereo microscope with an objective of ×0.5 (a and b, left) or ×1 (b, right) Scale bar corresponds to 2 mm (a and b, left) or 100 μm (b, right). (c) The FTIR spectra of calcium carbonate minerals precipitated at the edges of the colony. ν₂ and ν₃ indicate characteristic vibrations. The results are of a representative experiment out of five independent repeats.