Nucleation of calcium carbonate on microbial cell material may have been the dominant mode of microbial carbonate formation during most of Earth's history. Current knowledge predicts that nucleation takes place on the cell surface or on extracellular polymeric substances. However, the initial nucleation steps have not been described in detail and the process remains elusive. Here we describe the bacterial nucleation of calcium carbonate at the nanometer scale. In our precipitation experiment with sulfate reducing bacteria (SRB), the bulk of calcium carbonate precipitates on hundreds of individual globules 60-200 nm in diameter. Globules originate from the SRB cell surface but calcify significantly only when released to the culture medium. Similar globules have been observed, albeit at a much larger scale, in other bacterial precipitation experiments and in many natural microbial carbonates, suggesting that the process we describe could be an important step in microbial calcification.
Univ Kiel, Leibniz Inst Marine Sci, D-24148 Kiel, Germany; Univ Lyon 1, CNRS UMR 5125, Lab Paleoenvironm & Paleobiosphere, F-69622 Villeurbanne, France; Univ Paris 11, CNRS UMR 8502, Phys Solides Lab, F-91405 Orsay, France; Fed Inst Geosci & Nat Resources, D-30655 Hannover, Germany; Univ Kiel, Leibniz Inst Marine Sci, D-24148 Kiel, Germany; Univ Paris 06, CNRS UMR 7590, Lab Mineral & Cristallog Paris, F-75015 Paris, FranceArticleEnglish