Biomineralisation by earthworms – an investigation into the stability and distribution of amorphous calcium carbonate

Geochemical Transactions

Research Article

Bea Demarchi¹  Kirsty E H Penkman¹  Liane G Benning²  Juan D Rodriguez-Blanco³  Mark E Hodson⁴  Paul F Schofield⁵  Emma A A Versteegh⁶ 

[1] BioArCh, Departments of Chemistry and Archaeology, University of York, York, UK;Cohen Laboratories, School of Earth and Environment, University of Leeds, LS2 9JT, Leeds, UK;GFZ German Research Centre for Geosciences, Helmholtz Centre Potsdam, Telegrafenberg, 14473, Potsdam, Germany;Cohen Laboratories, School of Earth and Environment, University of Leeds, LS2 9JT, Leeds, UK;Nano-Science Center, Department of Chemistry, University of Copenhagen, 2100, Copenhagen, Denmark;Environment Department, University of York, YO10 5DD, York, UK;Mineral and Planetary Sciences, Department of Earth Sciences, Natural History Museum, SW7 5BD, London, UK;Soil Research Centre, Department of Geography and Environmental Science, School of Archaeology, Geography and Environmental Science, University of Reading, RG6 6DW, Wokingham, UK;NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, 91109, Pasadena, CA, USA;

关键词: Calcite;    ACC;    CaCO;    FTIR;    Synchrotron;    Amino acids;    Earthworms;    Stability;   

DOI  :  10.1186/s12932-015-0019-z

 received in 2014-12-19, accepted in 2015-04-15,  发布年份 2015

来源: Springer

【 摘 要 】

BackgroundMany biominerals form from amorphous calcium carbonate (ACC), but this phase is highly unstable when synthesised in its pure form inorganically. Several species of earthworm secrete calcium carbonate granules which contain highly stable ACC. We analysed the milky fluid from which granules form and solid granules for amino acid (by liquid chromatography) and functional group (by Fourier transform infrared (FTIR) spectroscopy) compositions. Granule elemental composition was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and electron microprobe analysis (EMPA). Mass of ACC present in solid granules was quantified using FTIR and compared to granule elemental and amino acid compositions. Bulk analysis of granules was of powdered bulk material. Spatially resolved analysis was of thin sections of granules using synchrotron-based μ-FTIR and EMPA electron microprobe analysis.ResultsThe milky fluid from which granules form is amino acid-rich (≤ 136 ± 3 nmol mg−1 (n = 3; ± std dev) per individual amino acid); the CaCO3 phase present is ACC. Even four years after production, granules contain ACC. No correlation exists between mass of ACC present and granule elemental composition. Granule amino acid concentrations correlate well with ACC content (r ≥ 0.7, p ≤ 0.05) consistent with a role for amino acids (or the proteins they make up) in ACC stabilisation. Intra-granule variation in ACC (RSD = 16%) and amino acid concentration (RSD = 22–35%) was high for granules produced by the same earthworm. Maps of ACC distribution produced using synchrotron-based μ-FTIR mapping of granule thin sections and the relative intensity of the ν2: ν4 peak ratio, cluster analysis and component regression using ACC and calcite standards showed similar spatial distributions of likely ACC-rich and calcite-rich areas. We could not identify organic peaks in the μ-FTIR spectra and thus could not determine whether ACC-rich domains also had relatively high amino acid concentrations. No correlation exists between ACC distribution and elemental concentrations determined by EMPA.ConclusionsACC present in earthworm CaCO3 granules is highly stable. Our results suggest a role for amino acids (or proteins) in this stability. We see no evidence for stabilisation of ACC by incorporation of inorganic components.Graphical abstractSynchrotron-based μ-FTIR mapping was used to determine the spatial distribution of amorphous calcium carbonate in earthworm-produced CaCO3 granules.

【 授权许可】

CC BY   
© Hodson et al.; licensee Springer. 2015. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.