PhD Student, Macquarie University
I study nanoscale properties of bivalve shells to see how they record environmental information
Bivalve shells are nano-composite materials consisting of crystalline calcium carbonate phases that are embedded within an organic scaffold. These two building blocks are arranged into highly hierarchical structures of different styles of arrangement. A detailed understanding of how bivalves produce and arrange these building blocks is of vital importance to decipher environmental and climatic information e.g., salinity, seawater temperature, and pH, which they record in their growing shells. In aquaculture experiments, I apply specific trace elements as labels to the waters in which the bivalves live and grow their shells. The labels are incorporated into the growth fronts of the shells and serve as snapshots to visualize the discrete, dynamic growth processes by applying high resolution micro-analytical instruments (e.g. nanoSIMS and Atom Probe). Aquaculture experiments have yielded positive results and are of high interest for the biomineralogical community.
Abstract: A detailed characterisation of the organic composition of Arctica islandica (Linnaeus, 1767) shells with homogenous microstructure is compared with nacroprismatic shells of Pinctada fucata martensii (Dunker, 1872), Hyriopsis cumingii (Lea, 1852) and Diplodon chilensis patagonicus (d’Orbigny, 1835). Thermogravimetric analysis shows lowest total organic contents of 1.65 wt% for A. islandica shells, while all nacroprismatic shells are higher (3.14–4.13 wt%). Macromolecules extracted from the nacroprismatic shells are dominated by hydrophobic amino acids (~ 54%) in the acid extracts, while EDTA-extracts are moderately rich in aspartate and glutamate (16% in total) and in glycine–alanine (42%). In comparison, A. islandica shells have higher concentrations of proline, glycine and aspartate (ca 40%). Infrared spectroscopy shows some acidic protein bands in A. islandica, which cannot be found in the nacroprismatic shells. Alcian Blue and/or modified silver staining methods reveal many prominent bands. Protein bands at around 10, 14, 17, 21, 26, 31, 40 and 55 kDa are detected in A. islandica shells for the first time, thus may constitute a new set of proteins in mollusc shells. SDS-PAGE exhibits apparent molecular weights from 5 to 63 kDa in nacroprismatic shells. Distinct protein bands at around 17 and 26 kDa in A. islandica shells may correspond to a post-translational modification of proteins; these prominent bands, however, are absent in the nacroprismatic samples. Contrarily, SDS-PAGE of both, homogeneous and nacroprismatic shell microstructures show nonacidic-matrix-proteins.
Pub.: 06 Oct '17, Pinned: 24 Apr '18