Biomineralization in calcifying marine organisms

The objective of this theses is to contribute to the wide discussion about the biological control level on the biomineralization operated by calcifying organisms. In particular the intra-crystalline organic matrix associated with different coral species was studied and its role in the process was investigated. The main goals obtained from the research on corals included: (i) the discovery of the species specific role of the intra-crystalline organic matrix molecules in the precipitation of calcium carbonate; (ii) the definition of the role of magnesium ions in the control of the macromolecules assembly/aggregation and in the consequent calcium carbonate polymorphic selectivity; (iii) the discovery that in corals the biomineralization process is not affected by the sea water acidity, as consequence corals are able to construct their skeletons independently from the environmental conditions as far they survive. At the same time, investigations on different kind of vaterite, biogenic and synthetic, were also carried out and confirm the importance of the organism control on the biomineralization process and in particular on the co-existence of different crystalline structures of vaterite for enabling optimization of specific functions, through the employment of OM and acidic macromolecules

Structure and Function of Stony Coral Intraskeletal Polysaccharides

Polysaccharides represent a main weight fraction of the intraskeletal organic matrix of corals, but their structure, as well as their function in the calcification process, has been poorly investigated. This communication shows by a combination of techniques (nuclear magnetic resonance, Fourier transform infrared, and monosaccharide composition) that their key component is a 1\u21923 \u3b2-d glucuronic acid polymer and evidences its influence in vitro in the calcification process

The Influence of a Protein Fragment Extracted from Abalone Shell Green Layer on the Precipitation of Calcium Carbonate Polymorphs in Aqueous Media

Many living organisms form mineral phases through biologically controlled processes, known as biomineralization. Thus created materials are composites of both, mineral and organic components. The shell of the gastropod mollusc red abalone (Haliotis rufescens) consists of calcite and aragonite layers, each of them containing characteristic biopolymers responsible for biomineralization. In this work, the effect of interstitial green sheet polypeptide, GP, extracted from the green layer of the mollusc red abalone shell, on the process of spontaneous precipitation of calcium carbonate polymorphs, was investigated. Three precipitation systems, in which the initial mineralogical composition of the precipitate was different, have been studied. Thus, in system (1) calcite appeared, in system (2) a mixture of calcite and vaterite was found, while in system (3), ASW, only aragonite precipitated. However, the precipitation kinetic measurements, X-ray diffraction, FT-IR spectroscopy, and light and scanning electron microscopy indicated that the addition of GP in the model systems caused the inhibition of precipitation and change of morphology of crystals as a consequence of GP adsorption on the crystal surfaces and its entrapment into the mineral structure. (doi: 10.5562/cca2197

The Skeletal Organic Matrix from Mediterranean Coral Balanophyllia europaea Influences Calcium Carbonate Precipitation

Scleractinian coral skeletons are made mainly of calcium carbonate in the form of aragonite. The mineral deposition occurs in a biological confined environment, but it is still a theme of discussion to what extent the calcification occurs under biological or environmental control. Hence, the shape, size and organization of skeletal crystals from the cellular level through the colony architecture, were attributed to factors as diverse as mineral supersaturation levels and organic mediation of crystal growth. The skeleton contains an intra-skeletal organic matrix (OM) of which only the water soluble component was chemically and physically characterized. In this work that OM from the skeleton of the Balanophyllia europaea, a solitary scleractinian coral endemic to the Mediterranean Sea, is studied in vitro with the aim of understanding its role in the mineralization of calcium carbonate. Mineralization of calcium carbonate was conducted by overgrowth experiments on coral skeleton and in calcium chloride solutions containing different ratios of water soluble and/or insoluble OM and of magnesium ions. The precipitates were characterized by diffractometric, spectroscopic and microscopic techniques. The results showed that both soluble and insoluble OM components influence calcium carbonate precipitation and that the effect is enhanced by their co-presence. The role of magnesium ions is also affected by the presence of the OM components. Thus, in vitro, OM influences calcium carbonate crystal morphology, aggregation and polymorphism as a function of its composition and of the content of magnesium ions in the precipitation media. This research, although does not resolve the controversy between environmental or biological control on the deposition of calcium carbonate in corals, sheds a light on the role of OM, which appears mediated by the presence of magnesium ions

Evidence of structural variability among synthetic and biogenic vaterite

Recently, the results of experimental and theoretical investigations have revealed that, in vaterite, two or even more crystalline structures coexist. In this communication we report evidence of diverse vaterite structures in biogenic samples of different origin. In addition, it is shown that the synthetic vaterite precipitated in the presence of poly-L-aspartate has structures similar to those of biogenic samples

Ecological relevance of skeletal fatty acid concentration and composition in Mediterranean scleractinian corals

The intra-skeletal fatty acid concentration and composition of four Mediterranean coral species, namely Cladocora caespitosa, Balanophyllia europaea, Astroides calycularis and Leptopsammia pruvoti, were examined in young and old individuals living in three different locations of the Mediterranean Sea. These species are characterized by diverse levels of organization (solitary or colonial) and trophic strategies (symbiotic or non-symbiotic). Fatty acids have manifold fundamental roles comprehensive of membrane structure fluidity, cell signaling and energy storage. For all species, except for B. europaea, the intra-skeletal fatty acid concentration was significantly higher in young individuals than in old ones. Moreover, fatty acid concentration was higher in colonial corals than in solitary ones and in the symbiotic corals compared to non-symbiotic ones. Analysis by gas chromatography-mass spectrometry (GC-MS) revealed that palmitic acid (16:0) was the most abundant fatty acid, followed by stearic (18:0) in order of concentration. Oleic acid (18:1) was detected as the third main component only in skeletons from symbiotic corals. These results suggest that, in the limits of the studied species, intra-skeletal fatty acid composition and concentration may be used for specific cases as a proxy of level of organization and trophic strategy, and eventually coral age

Ecological relevance of skeletal fatty acid concentration and composition in Mediterranean scleractinian corals

The intra-skeletal fatty acid concentration and composition of four Mediterranean coral species, namely Cladocora caespitosa, Balanophyllia europaea, Astroides calycularis and Leptopsammia pruvoti, were examined in young and old individuals living in three different locations of the Mediterranean Sea. These species are characterized by diverse levels of organization (solitary or colonial) and trophic strategies (symbiotic or non-symbiotic). Fatty acids have manifold fundamental roles comprehensive of membrane structure fluidity, cell signaling and energy storage. For all species, except for B. europaea, the intra-skeletal fatty acid concentration was significantly higher in young individuals than in old ones. Moreover, fatty acid concentration was higher in colonial corals than in solitary ones and in the symbiotic corals compared to non-symbiotic ones. Analysis by gas chromatography-mass spectrometry (GC-MS) revealed that palmitic acid (16:0) was the most abundant fatty acid, followed by stearic (18:0) in order of concentration. Oleic acid (18:1) was detected as the third main component only in skeletons from symbiotic corals. These results suggest that, in the limits of the studied species, intra-skeletal fatty acid composition and concentration may be used for specific cases as a proxy of level of organization and trophic strategy, and eventually coral age

Morphological and mechanical characterization of composite calcite/SWCNT\u2013COOH single crystals

A growing number of classes of organic (macro) molecular materials have been trapped into inorganic crystalline hosts, such as calcite single crystals, without significantly disrupting their crystalline lattices. Inclusion of an organic phase plays a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals. Here we report the synthesis and mechanical characterization of composite calcite/SWCNT-COOH single crystals. Once entrapped into the crystals SWCNT-COOH appeared both as aggregates of entangled bundles and nanoropes. Their observation was possible only after crystal etching, fracture or FIB (focused ion beam) cross-sectioning. SWCNT-COOHs occupied a small volume fraction and were randomly distributed into the host crystal. They did not strongly affect the crystal morphology. However, although the Young's modulus of composite calcite/SWCNT-COOH single crystals was similar to that of pure calcite their hardness increased by about 20%. Thus, SWCNT-COOHs provide an obstacle against the dislocation-mediated propagation of plastic deformation in the crystalline slip systems, in analogy with the well-known hardness increase in fiber-reinforced composites

Polypeptide effect on Mg2+hydration inferred from CaCO3formation: a biomineralization study by counter-diffusion

The use of a counter-diffusion system allows the evaluation of diverse parameters involved in a crystallization process. In this study, this tool has been used to infer the hydration status of Mg2+ during CaCO3 formation experiments in an agarose highly viscous sol entrapping charged polypeptides. The experimental data allow us to infer that the hydration status of Mg2+ is altered by the presence of poly-L-aspartate or poly-L-glutamate. This changes the CaCO3 polymorphic distribution in favor of Mg-calcite with respect to aragonite, but does not favor the isomorphic substitution of Mg2+ with Ca2+ within the calcite lattice. The latter may exclude the formation of an amorphous transient form, which leads to a high Mg-calcite, as expected when using a counter-diffusion system set up. The presence of poly-L-lysine does not affect the hydration of Mg2+, but favors the formation of aragonite with respect to calcite. In this case an inhibition of calcite formation and an alteration of the hydration sphere of Ca2+ could be invoked; both effects are able to increase CaCO3 supersaturation. In conclusion, this study reveals that charged polypeptides can orchestrate CaCO3 formation by also controlling the hydration status of cations