Organic Matrices of Calcium Carbonate Biominerals Improve Osteoblastic Mineralization

Many organisms incorporate inorganic solids into their tissues to improve functional and mechanical properties. The resulting mineralized tissues are called biominerals. Several studies have shown that nacreous biominerals induce osteoblastic extracellular mineralization. Among them, Pinctada margaritifera is well known for the ability of its organic matrix to stimulate bone cells. In this context, we aimed to study the effects of shell extracts from three other Pinctada species (Pinctada radiata, Pinctada maxima, and Pinctada fucata) on osteoblastic extracellular matrix mineralization, by using an in vitro model of mouse osteoblastic precursor cells (MC3T3-E1). For a better understanding of the Pinctada-bone mineralization relationship, we evaluated the effects of 4 other nacreous mollusks that are phylogenetically distant and distinct from the Pinctada genus. In addition, we tested 12 non-nacreous mollusks and one extra-group. Biomineral shell powders were prepared, and their organic matrix was partially extracted using ethanol. Firstly, the effect of these powders and extracts was assessed on the viability of MC3T3-E1. Our results indicated that neither the powder nor the ethanol-soluble matrix (ESM) affected cell viability at low concentrations. Then, we evaluated osteoblastic mineralization using Alizarin Red staining and we found a prominent MC3T3-E1 mineralization mainly induced by nacreous biominerals, especially those belonging to the Pinctada genus. However, few non-nacreous biominerals were also able to stimulate the extracellular mineralization. Overall, our findings validate the remarkable ability of CaCO3 biomineral extracts to promote bone mineralization. Nevertheless, further in vitro and in vivo studies are needed to uncover the mechanisms of action of biominerals in bone.

A highlightedly improved method for isolating and characterizing calcium oxalate crystals from tubercles of Mammillaria schumannii

BACKGROUND

Calcium oxalate (CaOx) is the most prevalent and widespread biomineral in plants and is involved in protective and/or defensive functions against abiotic stress factors. It is, however, expected that this function has an extremely significant contribution to growth processes in plants bearing large amounts of CaOx, such as cacti growing in desert environment.

RESULTS

In our research, small-sized CaOx crystals (≤ 20 µm) with tetrahedral or spherical shapes were observed to dominate in each epidermal and cortical cell from the tubercles of Mammillaria schumannii, a species from the Cereoideae subfamily, having tubercles (main photosynthetic organs) united with adjacent ones almost into ridges on its stem. Because they have potential significant functions, differential centrifugations after mechanical blending were used to obtain these small-sized CaOx crystals, which extremely tend to adhere to tissue or suspend in solution. And then the combined Scanning Electron Microscope Energy Dispersive System (SEM-EDS) and Raman spectroscopy were further performed to demonstrate that the extracted crystals were mainly CaC2O4·2H2O. Interestingly, spherical druses had 2 obvious abnormal Raman spectroscopy peaks of -CH and -OH at 2947 and 3290 cm-1, respectively, which may be attributed to the occluded organic matrix. The organic matrix was further extracted from spherical crystals, which could be polysaccharide, flavone, or lipid compounds on the basis of Raman spectroscopy bands at 2650, 2720, 2770, and 2958 cm-1.

CONCLUSIONS

Here we used a highlightedly improved method to effectively isolate small-sized CaOx crystals dominating in the epidermal and cortical cells from tubercles of Mammillaria schumannii, which extremely tended to adhere plant tissues or suspend in isolation solution. And then we further clarified the organic matrix getting involved in the formation of CaOx crystals. This improved method for isolating and characterizing biomineral crystals can be helpful to understand how CaOx crystals in cacti function against harsh environments such as strong light, high and cold temperature, and aridity.

Insight into biomolecular interaction-based non-classical crystallization of bacterial biocement

In an attempt to draw a correlation between calcium carbonate (CaCO3) precipitation and biomacromolecules such as extracellular polymeric substances and enzyme activity in biomineralizing microbe, this report aims to elucidate the ureolytic and ammonification route in Paenibacillus alkaliterrae to explore the possible role of organic biomolecule(s) present on cell surface in mediating nucleation and crystallization of biogenic CaCO3. After 168 h of biomineralization in ureolysis and ammonification, 2.2 g/l and 0.87 g/l of CaCO3 precipitates were obtained, respectively. The highest carbonic anhydrase activity (31.8 µmoles/min/ml) was evidenced in ammonification as opposed to ureolysis (24.8 µmoles/min/ml). Highest urease activity reached up to 9.26 µmoles/min/ml in ureolytic pathway. Extracellular polymeric substances such as polysaccharides and proteins were found to have a vital role not only in the nucleation and crystal growth but also in addition direct polymorphic fate of CaCO3 nanoparticles. EPS production was higher during ammonification (3.1 mg/ml) than in ureolysis (0.72 mg/ml). CaCO3 nanoparticle-associated proteins were found to be 0.82 mg/ml in ureolysis and 0.56 mg/ml in ammonification. After 30 days of biomineralization, all the polymorphic forms stabilized to calcite in ureolysis but in ammonification vaterite predominated. In our study, we showed that organic template-mediated prokaryotic biomineralization follows the non-classical nucleation and varying proportions of these organic components causes selective polymorphism of CaCO3 nanoparticles. Overall, the findings are expected to further the fundamental understanding of enzymes, EPS-driven non-classical nucleation of CaCO3, and we foresee the design of fit-for-purpose futuristic biominerals arising from such renewed understanding of biomineralization. KEY POINTS: • Organic-inorganic interface of cell surface promote crystallization of biominerals • Carbohydrate and proteins in the interface results selective polymorphism of CaCO3 • Calcite stabilized at 30 days in ureolysis, vaterite-calcite mix in ammonification.

In situ mapping of biomineral skeletal proteins by molecular recognition imaging with antibody-functionalized AFM tips

Spatial localizing of skeletal proteins in biogenic minerals remains a challenge in biomineralization research. To address this goal, we developed a novel in situ mapping technique based on molecular recognition measurements via atomic force microscopy (AFM), which requires three steps: (1) the development and purification of a polyclonal antibody elicited against the target protein, (2) its covalent coupling to a silicon nitride AFM tip ('functionalization'), and (3) scanning of an appropriately prepared biomineral surface. We applied this approach to a soluble shell protein - accripin11 - recently identified as a major component of the calcitic prisms of the fan mussel Pinna nobilis [1]. Multiple tests reveal that accripin11 is evenly distributed at the surface of the prisms and also present in the organic sheaths surrounding the calcitic prisms, indicating that this protein is both intra- and inter-crystalline. We observed that the adhesion force in transverse sections is about twice higher than in longitudinal sections, suggesting that accripin11 may exhibit preferred orientation in the biomineral. To our knowledge, this is the first time that a protein is localized by molecular recognition atomic force microscopy with antibody-functionalized tips in a biogenic mineral. The 'pros' and 'cons' of this methodology are discussed in comparison with more 'classical' approaches like immunogold. This technique, which leaves the surface to analyze clean, might prove useful for clinical tests on non-pathological (bone, teeth) or pathological (kidney stone) biomineralizations. Studies using implants with protein-doped calcium phosphate coating can also benefit from this technology. STATEMENT OF SIGNIFICANCE: Our paper deals with an unconventional technical approach for localizing proteins that are occluded in biominerals. This technique relies on the use of molecular recognition atomic force microscopy with antibody-functionalized tips. Although such approach has been employed in other system, this is the very first time that it is developed for biominerals. In comparison to more classical approaches (such as immunogold), AFM microscopy with antibody-functionalized tips allows higher magnification and keeps the scanned surface clean for other biophysical characterizations. Our method has a general scope as it can be applied in human health, for non-pathological (bone, teeth) and pathological (kidney stone) biomineralizations as well as for bone implants coated with protein-doped calcium phosphate.

Otolin-1, an otolith- and otoconia-related protein, controls calcium carbonate bioinspired mineralization

BACKGROUND

Otoliths and otoconia are calcium carbonate biomineral structures that form in the inner ear of fish and humans, respectively. The formation of these structures is tightly linked to the formation of an organic matrix framework with otolin-1, a short collagen-like protein from the C1q family as one of its major constituents.

METHODS

In this study, we examined the activity of recombinant otolin-1 originating from Danio rerio and Homo sapiens on calcium carbonate bioinspired mineralization with slow-diffusion method and performed crystals characterization with scanning electron microscopy, two-photon excited fluorescence microscopy, confocal laser scanning microscopy and micro-Raman spectroscopy.

RESULTS

We show that both proteins are embedded in the core of CaCO₃ crystals that form through the slow-diffusion mineralization method. Both of them influence the morphology but do not change the polymorphic mineral phase. D.rerio otolin-1 also closely adheres to the crystal surface.

GENERAL SIGNIFICANCE

The results suggest, that otolin-1 is not a passive scaffold, but is directly involved in regulating the morphology of the resulting calcium carbonate biocrystals.

Mineralogy, geochemistry, 13C and 16O isotopic characteristics of urinary stones in Iran, a case study of Lorestan Province

Owing to the importance of urinary stones as one of the biominerals in the human body, it is necessary to investigate their chemical composition and mineralogy. In this matter, a mineralogical study using X-ray diffraction and scanning electron microscopy indicated that urinary stones in Lorestan Province were divided into 5 groups of calcium oxalate, urate, cysteine, phosphate and mixed stones (Whewellite, uric acid, phosphate). In this regard, the microscopic studies revealed that Whewellite was the most important mineral phase among various phases. In the following, the major and rare elements of each group were determined by inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence analysis. The obtained results demonstrated that Ca was found the most abundant element in urinary stones. In the analysis results of the major oxides, compared to other major oxides, CaO had the highest frequency in urinary stones. The reason was due to the role of calcium in most of the basic functions in cell metabolism. The average values of isotope ¹³C and ¹⁶O in the studied urinary stones were obtained - 33.71 and - 20.57, respectively. Overall, the values of ¹³C isotope in urinary stones were lower than those in the similar stones and human hard tissues in other countries.

Selenium-doped calcium phosphate biomineral reverses multidrug resistance to enhance bone tumor chemotherapy

The construction of a functional drug delivery system to reverse the multidrug resistance (MDR) of bone tumors in cases of failed chemotherapy remains a challenge. Herein, we demonstrate a selenium-doped calcium phosphate (Se-CaP) biomineral with high biocompatibility, biodegradability and pH-sensitive drug release properties. Se-CaP may not only serve as an effective drug-carrier to enhance the uptake of doxorubicin (DOX), but may also synchronously induce caspases-mediated apoptosis of osteosarcoma by generating intracellular reactive oxygen species (ROS). Furthermore, in vitro and in vivo studies obviously demonstrate that Se-CaP can reverse the MDR of osteosarcoma by down-regulating the expression of MDR-related ABC (ATP binding cassette) transporters proteins (ABCB1 and ABCC1). Finally, DOX-loaded Se-CaP can significantly inhibit DOX-resistant MG63 (MG63/DXR) tumor growth in nude mice. Considering its biomimetic chemical properties, the Se-CaP biomineral, with the multiple functions mentioned above, could be a promising candidate for treating bone tumors with MDR characteristics.

Mollusc shellomes: Past, present and future

In molluscs, the shell fabrication requires a large array of secreted macromolecules including proteins and polysaccharides. Some of them are occluded in the shell during mineralization process and constitute the shell repertoire. The protein moieties, also called shell proteomes or, more simply, 'shellomes', are nowadays analyzed via high-throughput approaches. These latter, applied so far on about thirty genera, have evidenced the huge diversity of shellomes from model to model. They also pinpoint the recurrent presence of functional domains of diverse natures. Shell proteins are not only involved in guiding the mineral deposition, but also in enzymatic and immunity-related functions, in signaling or in coping with many extracellular molecules such as saccharides. Many shell proteins exhibit low complexity domains, the function of which remains unclear. Shellomes appear as self-organizing systems that must be approached from the point of view of complex systems biology: at supramolecular level, they generate emergent properties, i.e., microstructures that cannot be simply explained by the sum of their parts. A conceptual scheme is developed here that reconciles the plasticity of the shellome, its evolvability and the constrained frame of microstructures. Other perspectives arising from the study of shellomes are briefly discussed, including the macroevolution of shell repertoires, their maturation and their transformation through time.

Chemical data on environmental matrices from an abandoned mining site

This article contains analytical data on chemical composition of waters and solid samples (mining wastes and biominerals) collected in an abandoned mining area, and they are related with the research article "Geochemistry of rare earth elements in water and solid materials at abandoned mines in SW Sardinia (Italy)" (Medas et al., 2013). Specifically, we present physicochemical data (temperature, electrical conductivity, pH, and redox potential), major components and the main contaminants (Zn, Mn, Cd, Ni, Cu, Pb) detected in stream waters and drainages from mine wastes. Waters were monitored from 2009 to 2011 during different seasonal conditions to give an insight into metal dispersion under different hydrological conditions.

Chitosan enhances calcium carbonate precipitation and solidification mediated by bacteria

Formation of the biominerals in living organisms is mainly associated with organic macromolecules. These organic materials play an important role in the nucleation, growth, and morphology controls of the biominerals. Current study mimics this concept of organic matrix- mediated biomineralization by using microbial induced carbonate precipitation (MICP) method in combination with the cationic polysaccharide chitosan. CaCO₃ precipitation was performed by the hydrolysis of urea by the ureolytic bacteria Pararhodobacter sp. SO1 in the presence of CaCl₂, with and without chitosan. The crystal polymorphism and morphology of oven-dried samples were analyzed by X-ray diffraction and scanning electron microscopy. The amount of precipitate obtained was higher in the presence of chitosan. The precipitate included both of the CaCO₃ and the chitosan hydrogel. Rhombohedral crystals were dominant in the precipitate without chitosan and distorted crystal agglomerations were found with chitosan. Sand solidification experiments were conducted in the presence of chitosan under different experimental conditions. By adding chitosan, more strongly cemented sand specimens could be obtained than those from conventional method. All of these results confirm the positive effect of chitosan for the CaCO₃ precipitation and sand solidification.

Data on rare earth elements in mining environments under non-acidic conditions

This article contains analytical data on Rare Earth Elements (REE) concentration in waters and solid samples (mining wastes and biominerals) collected in an abandoned mining site characterized by near-neutral conditions, and they are related with the research article “Geochemistry of rare earth elements in water and solid materials at abandoned mines in SW Sardinia (Italy)” (Medas et al., 2013).

REE can show specific signatures due to fractionation processes, giving an insight to the understanding of the natural processes ruling the water–rock interactions and the geo–bio-interactions. Most researches on REE behavior were performed in acidic environments, while only few data on REE are available for neutral waters. Elaboration of this dataset can be useful to evaluate the reactions controlling the geochemical behavior of REE under near-neutral to slightly alkaline conditions, driving the scientific community toward an efficient management of monitoring actions and remediation technologies.

Manganese enhances the immobilization of trace cadmium from irrigation water in biological soil crust

The effect of biological soil crust (BSC) in paddy field on the immobilization and removal of heavy metal from irrigation water is an important issue. BSC was cultured in solutions with different concentrations of manganese (Mn) salt and cadmium (Cd) sulfate for 15 days. We analyzed the Mn, Cd and Fe contents in the BSC and investigated the effects of Mn salt on the Cd distribution in different binding-forms in BSC as well. The results show that Mn salt was effective at enabling BSC to immobilize the Cd, and its removal efficiency from irrigation water improved with an increase in the Mn concentration used. The removal of 50.00 μg/L of Cd from irrigation water by BSC reached as high as 95.70% in present of 20.00 mg/L Mn. The highest obtained biological concentrated factor of BSC for Cd is ~2.7 × 10⁴. The mainly Cd species (75%) in BSC is the non-EDTA extracted minerals. Based on the SEM-EDS and XPS analyses, it was reasonably inferred that the Mn ion was oxidized by Mn oxidizing bacteria (MOB), to yield the porous spongy-like birnessite with d-spacing of 2.31 Ǻ, while Cd was scavenged and immobilized in the crystal lattice. The MOB was identified as Bacillus. This study provides a potentially novel method to decontaminate irrigation water polluted with Cd by using BSC in presence of Mn.

Fluid-flow-templated self-assembly of calcium carbonate tubes in the laboratory and in biomineralization: The tubules of the watering-pot shells, Clavagelloidea

We show with laboratory experiments that self-assembled mineral tube formation involving precipitation around a templating jet of fluid - a mechanism well-known in the physical sciences from the tubular growth of so-called chemical gardens - functions with carbonates, and we analyse the microstructures and compositions of the precipitates. We propose that there should exist biological examples of fluid-flow-templated tubes formed from carbonates. We present observational and theoretical modelling evidence that the complex structure of biomineral calcium carbonate tubules that forms the 'rose' of the watering-pot shells, Clavagelloidea, may be an instance of this mechanism in biomineralization. We suggest that this is an example of self-organization and self-assembly processes in biomineralization, and that such a mechanism is of interest for the production of tubes as a synthetic biomaterial.

STATEMENT OF SIGNIFICANCE

The work discussed in the manuscript concerns the self-assembly of calcium carbonate micro-tubes and nano-tubes under conditions of fluid flow together with chemical reaction. We present the results of laboratory experiments on tube self-assembly together with theoretical calculations. We show how nature may already be making use of this process in molluscan biomineralization of the so-called watering-pot shells, and we propose that we may be able to take advantage of the formation mechanism to produce synthetic biocompatible micro- and nano-tubes.

Photosynthetic biomineralization of radioactive Sr via microalgal CO2 absorption

Water-soluble radiostrontium ((90)Sr) was efficiently removed as a carbonate form through microalgal photosynthetic process. The immobilization of soluble (90)Sr radionuclide and production of highly-precipitable radio-strontianite ((90)SrCO3) biomineral are achieved by using Chlorella vulgaris, and the biologically induced mineralization drastically decreased the (90)Sr radioactivity in water to make the highest (90)Sr removal ever reported. The high-resolution microscopy revealed that the short-term removal of soluble (90)Sr by C. vulgaris was attributable to the rapid and selective carbonation of (90)Sr together with the consumption of dissolved CO2 during photosynthesis. A small amount of carbonate in water could act as Sr(2+) sinks through the particular ability of the microalga to make the carbonate mineral of Sr stabilized firmly at the surface site.

X-ray microdiffraction of biominerals

Biominerals have complex and heterogeneous architectures, hence diffraction experiments with spatial resolutions between 500 nm and 10 μm are extremely useful to characterize them. X-ray beams in this size range are now routinely produced at many synchrotrons. This chapter provides a review of the different hard X-ray diffraction and scattering techniques, used in conjunction with efficient, state-of-the-art X-ray focusing optics. These include monochromatic X-ray microdiffraction, polychromatic (Laue) X-ray microdiffraction, and microbeam small-angle X-ray scattering. We present some of the most relevant discoveries made in the field of biomineralization using these approaches.

CaCO₃ vaterite microparticles for biomedical and personal care applications

Among the polymorph modifications of calcium carbonate, the metastable vaterite is the most practically important. Vaterite particles are applied in regenerative medicine, drug delivery and a broad range of personal care products. This manuscript scopes to review the mechanism of the calcium carbonate crystal growth highlighting the factors stabilizing the vaterite polymorph in the most cost efficient synthesis routine. The size of vaterite particles is a crucial parameter for practical applications. The options for tuning the particle size are also discussed.

Identification of a frustule-associated protein of the marine pennate diatom Fistulifera sp. strain JPCC DA0580

Among the proteins localized on the cell wall (frustule) of diatoms (frustule-associated proteins), several proteins tightly associated with the cell wall have been implicated in frustule formation. These proteins include diatom-specific unique serine- and lysine-rich sequences represented by silaffins. Taking advantage of available genome information, we used a recently described bioinformatics approach to screen silaffin-like proteins rich in serine and lysine from the genome of the marine pennate diatom Fistulifera sp. strain JPCC DA0580 and identified 7 proteins. All of the proteins shared a sequence motif called the XGXG domain, which was also confirmed in a silaffin-like protein identified in other diatoms. In vivo localization analysis revealed that one of the identified proteins, G7408, occurs throughout the frustule with a slightly uneven distribution. This novel frustule-associated protein could be a useful tool to elucidate the mechanism of biosilica formation in diatoms and to functionalize this strain for future biotechnological applications.

Crystal nucleation and near-epitaxial growth in nacre

Nacre is the iridescent inner lining of many mollusk shells, with a unique lamellar structure at the sub-micron scale, and remarkable resistance to fracture. Despite extensive studies, nacre formation mechanisms remain incompletely understood. Here we present 20-nm, 2°-resolution polarization-dependent imaging contrast (PIC) images of shells from 15 mollusk species, mapping nacre tablets and their orientation patterns. These data show where new crystal orientations appear and how similar orientations propagate as nacre grows. In all shells we found stacks of co-oriented aragonite (CaCO₃) tablets arranged into vertical columns or staggered diagonally. Near the nacre-prismatic (NP) boundary highly disordered spherulitic aragonite is nucleated. Overgrowing nacre tablet crystals are most frequently co-oriented with the underlying aragonite spherulites, or with another tablet. Away from the NP-boundary all tablets are nearly co-oriented in all species, with crystal lattice tilting, abrupt or gradual, always observed and always small (plus or minus 10°). Therefore aragonite crystal growth in nacre is near-epitaxial. Based on these data, we propose that there is one mineral bridge per tablet, and that "bridge tilting" may occur without fracturing the bridge, hence providing the seed from which the next tablet grows near-epitaxially.

Crystal lattice tilting in prismatic calcite

We analyzed the calcitic prismatic layers in Atrina rigida (Ar), Haliotis iris (Hi), Haliotis laevigata (HL), Haliotis rufescens (Hrf), Mytilus californianus (Mc), Pinctada fucata (Pf), Pinctada margaritifera (Pm) shells, and the aragonitic prismatic layer in the Nautilus pompilius (Np) shell. Dramatic structural differences were observed across species, with 100-μm wide single-crystalline prisms in Hi, HL and Hrf, 1-μm wide needle-shaped calcite prisms in Mc, 1-μm wide spherulitic aragonite prisms in Np, 20-μm wide single-crystalline calcite prisms in Ar, and 20-μm wide polycrystalline calcite prisms in Pf and Pm. The calcite prisms in Pf and Pm are subdivided into sub-prismatic domains of orientations, and within each of these domains the calcite crystal lattice tilts gradually over long distances, on the order of 100 μm, with an angle spread of crystal orientation of 10-20°. Furthermore, prisms in Pf and Pm are harder than in any other calcite prisms analyzed, their nanoparticles are smaller, and the angle spread is strongly correlated with hardness in all shells that form calcitic prismatic layers. One can hypothesize a causal relationship of these correlated parameters: greater angle spread may confer greater hardness and resistance to wear, thus providing Pf and Pm with a structural advantage in their environment. This is the first structure-property relationship thus far hypothesized in mollusk shell prisms.