Lipids from the nacreous and prismatic layers of two Pteriomorpha mollusc shells

Mollusc shells are acellular biominerals, in which macromolecular structures are intimately associated with mineral phases. Most studies are devoted to proteins, despite sugars have been described. Lipids were extracted from the calcite prismatic and aragonite nacreous layer of two mollusc shells. Fourier Transform Infrared Spectrometry shows that lipids are present in both samples, but they are not similar. Thin layer chromatography confirms that lipids are different in the two studied layers, so that it may be suggested they are species-dependant. Although not yet deciphered, their role in biomineralization and fossilisation processes is probably important.

Structural, mineralogical, and biochemical diversity in the lower part of the pearl layer of cultivated seawater pearls from Polynesia

A series of Polynesian pearls has been investigated with particular attention to the structural and compositional patterns of the early developmental stages of the pearl layer. These initial steps in pearl formation bear witness of the metabolic changes that have occurred during the pearl-sac formation. The resulting structurally and biochemically complex structures have been investigated using a variety of techniques that provide us with information concerning both mineral phases and the organic components. Results are discussed with respect to our understanding of the biomineralization mechanisms, as well as for the grafting process.

Subdaily growth patterns and organo-mineral nanostructure of the growth layers in the calcitic prisms of the shell of Concholepas concholepas Bruguière, 1789 (Gastropoda, Muricidae)

Fluorochrome marking of the gastropod Concholepas concholepas has shown that the prismatic units of the shell are built by superimposition of isochronic growth layers of about 2 mum. Fluorescent growth marks make it possible to establish the high periodicity of the cyclic biomineralization process at a standard growth rhythm of about 45 layers a day. Sulphated polysaccharides have been identified within the growth layers by using synchrotron radiation, whereas high resolution mapping enables the banding pattern of the mineral phase to be correlated with the layered distribution of polysaccharides. Atomic force microscopy has shown that the layers are made of nanograins densely packed in an organic component.

Monohydrocalcite in calcareous corpuscles of Mesocestoides corti

Mesocestoides corti (syn. vogae), as many other cestode platyhelminthes, contains abundant mineralized structures called calcareous corpuscles. These concretions may constitute as much as 40% of the dry weight of the organisms, but their function remains poorly understood. In this work, we reviewed the mineral composition of the calcareous corpuscles of M. corti. X-ray diffraction pattern showed that the major mineral component of the corpuscles is a hydrated form of calcium carbonate, monohydrocalcite, also confirmed by infrared spectrometry. The baseline shift of the X-ray diffraction spectra suggested the presence of amorphous calcium carbonate, accordingly to previous reports, and an organic matrix was confirmed by FTIR. Monohydrocalcite is a rare mineral unusually found in biominerals. Although the significance of monohydrocalcite in biominerals has not been determined, the knowledge of corpuscles composition is of relevance to establish their function and for the elucidation of the mechanisms involved in mineralization processes.

Microstructure and chemical composition of giant avian eggshells

The microstructure and composition of the layers of two giant avian eggshells were investigated using a combination of scanning electron microscopy, electron probe microanalyses, and X-ray absorption near-edge structure spectroscopy (XANES). The two species have some similarities and differences in their microstructure and composition; the composition is not homogeneous throughout the eggshell thickness. XANES studies show that sulfur is associated with amino acids in the inner organic membranes, whereas in the mineralised layers the sulfur is mainly associated with sulfated polysaccharides. These results are similar to those obtained on chicken eggshells, and confirm the active role of sulfated acidic polysaccharides in biomineralisation processes of carbonate skeletons.

Mineralizing matrices in the skeletal axes of two Corallium species (Alcyonacea)

Soluble organic matrices extracted from the axial part of the skeletons of two Corallium species (Coralliidae, Alcyonacea) were analysed using FTIR spectrometry, HPLC, IEF, 2-D gel electrophoresis and XANES. All these methods show that the main characteristics of the two matrices are similar, but not identical. Both matrices are composed of proteins and sugars; they are acidic with poorly separated molecular masses. The sugar contents are low, and the matrices do not seem highly glycosylated. The differences and similarities of these matrices are also observed in the minor element contents and in the micro- and nanostructures of the samples. These results confirm the control of the morphology and the chemical composition of calcitic biocrystals. Biomineralisation processes in Coralliidae are taxonomically significant, and differ from those of Scleractinia skeletons.

Structure and composition of the septal nacreous layer of Nautilus macromphalus L. (Mollusca, Cephalopoda)

The nacreous layer of Mollusca is the best-known aragonitic structure and is the usual model for biomineralization. However, data are based on less than 10 species. In situ observations of the septal nacreous layer of the cephalopod Nautilus shell has revealed that the tablets are composed of acicular laths. These laths are composed of round nanograins surrounded by an organic sheet. No hole has been observed in the decalcified interlamellar membranes. A set of combined analytical data shows that the organic matrices extracted from the nacreous layer are glycoproteins. In both soluble and insoluble matrices, S amino acids are rare and the soluble organic matrices have a higher sulfated sugar content than the insoluble matrices. It is possible that the observed differences in the structure and composition of the nacreous layers of the outer wall and septa of the Nautilus shell have a dual origin: evolution and functional adaptation. However, we have no appropriate data as yet to answer this question.

The two-step mode of growth in the scleractinian coral skeletons from the micrometre to the overall scale

It has been known since the 19th century that coral skeletons are built of aragonite crystals with taxonomy-linked arrangements, but the way by which each coral species controls this crystallization process remains an unsolved question. The problem became still more intriguing when it was shown that isotopic compositions of coral aragonite were subject to taxonomy-linked influences (the "vital effect"). On the other hand, presence of an organic component in coral skeletons is also long known, but localization of these compounds is admittedly restricted to particular structures called "centres of calcifications." Fibres, the largely predominant part of the coral skeletons, are usually considered as purely mineral units. In this paper, it is shown that in both "centres of calcification" and fibres, organic compounds are associated with the mineral material at a deep structural level. A series of variously scaled observations and localized measurements allow recognition of the presence of an organic component at the nanometre scale. Far from being a freely operating process, crystallization of coral fibres is thus permanently controlled by the polyp basal ectoderm through a cyclic two-step process acting at the micrometre-scale. The biomineralization cycle begins by secretion of a proteoglycan matrix. As the composition of these sugars-proteins assemblages has been shown taxonomy dependent, the hypothesis can be made that multiple and long recognized specificities of coral skeletons are linked to this biochemically driven crystallization process. Additionally, this new concept of the biomineralization process in coral skeletons provides us with an access to the long term evolution of the Scleractinia. Remarkably, results of a skeleton-based approach using microstructural criteria (i.e., the spatial relationships of "centres of calcification" and the three-dimensional arrangements of fibres), are consistent with a molecular phylogenetic analysis carried out on the same species. Clearly, at the overall ontogenic level, the two-step growth mode of coral skeletons is also a valuable tool to reconstruct the evolutionary history of Scleractinia.

In situ chemical speciation of sulfur in calcitic biominerals and the simple prism concept

The microstructure and composition of two mollusc shells were investigated using a combination of light microscopy, SEM, EPMA, and XANES. The shells of Pinna and Pinctada are composed of calcite prisms separated by organic walls. The prismatic units of Pinna are monocrystalline, and those of Pinctada are polycrystalline with internal organic radial membranes. High-spatial-resolution XANES maps for the different S species across adjacent prisms show that sulfate is the principal component in both the intraprismatic organic matrices and the outer membranes. Additionally, these maps confirm that the inner structures of the prismatic units are different for both genera. In many ways, the prisms of Pinna and Pinctada are different and invalidate the "simple prism" concept.

Soluble organic matrices of the calcitic prismatic shell layers of two Pteriomorphid bivalves. Pinna nobilis and Pinctada margaritifera

The calcitic prisms of the shells of two bivalves, Pinna and Pinctada, are considered simple prisms according to some morphological and mineralogical characteristics. Scanning electron microscopic and atomic force microscopic studies show that the microstructures and nanostructures of these two shells are different. Pinna prisms are monocrystalline, whereas Pinctada prisms are not. Moreover, intraprismatic membranes are present only in the Pinctada prisms. The soluble organic matrices extracted from these prisms are acidic, but their bulk compositions differ. Ultraviolet and infrared spectrometries, fluorescence, high pressure liquid chromatography, and electrophoresis show that the sugar-protein ratios and the molecular weights are different. Sulfur is mainly associated with acidic sulfated sugars, not with amino acids, and the role of acidic sulfated sugars is still underestimated. Thus, the simple prism concept is not a relevant model for the biomineralization processes in the calcitic prismatic layer of mollusk shells.

Composition and properties of the soluble organic matrix of the otolith of a marine fish: Gadus morhua Linne, 1758 (Teleostei, Gadidae)

The soluble matrix of the sagittal otolith of the cod Gadus morhua was analyzed using UV and IR spectroscopy, liquid chromatography and electrophoresis. This matrix is a complex mixture of proteins and glycoproteins, with a large range of molecular weights. High weights (>1000 kDa) are shown for the first time in water-soluble matrix of otolith. However, the 2D denaturing electrophoresis and large range of sorting used in high performance liquid chromatography columns do not separate the soluble matrix to well-defined molecular weights. The IR data indicate that several conformations are present and the main part of the sugars is not sulfated. Additionally, electrophoresis data show that the acidity of the sugar components is higher than that of the proteins. Despite the relative scarcity of literature data, our study of G. morhua suggests that the chemical composition of otolith soluble organic matrix may differ among species.

Comparison of the soluble matrices of the calcitic prismatic layer of Pinna nobilis (Mollusca, Bivalvia, Pteriomorpha)

The calcitic prisms of the outer layer of the shell of Pinna nobilis, surrounded by thick organic walls, contain a soluble intracrystalline matrix. The structure and composition of the outer interprismatic walls are not well known. The current viewpoint is they are composed of an insoluble matrix. Another thick organic structure, the interlamellar sheet of the nacreous layer, is composed of insoluble and soluble matrices. The composition of two sets of soluble organic matrices from the calcitic layer of Pinna nobilis, extracted with and without the organic walls are compared. According to the various analyses (SEM and AFM, UV and FTIR spectrometry, HPLC, electrophoreses, XANES), the main characteristics of the two matrices are similar, but not identical. Thus, the organic walls contain soluble components. However, the three-layered structure of the interlamellar sheet of the nacreous layer has not been observed.

Comparative studies of skeletal soluble matrices from some Scleractinian corals and Molluscs

The soluble organic matrices extracted from aragonitic skeletons of five Scleractinia and two Molluscs were analyzed using FTIR spectrometry, HPLC and 2-D gel electrophoresis. All these methods show that scleractinian and molluscan matrices are different. Both matrices are acidic with poorly separated molecular weights. The scleractinian matrices are highly glycosylated, whereas the molluscan matrices are not as shown by stains in 2D-electrophoresis. These results were in accordance with earlier data: high S contents in Scleractinia skeletons and low S contents in Mollusca shells. These results confirm the control of the morphology and the chemical composition of aragonite biocrystals in various taxa.

La diagenese des otolithes par la comparaison des donnees microstructurales, mineralogiques et geochimiques; application aux fossiles du Pliocene du Sud-Est de la France

Microstructure, mineralogy and elemental and isotopic compositions of recent and fossil otoliths have been investigated. Fossil otoliths come from marine Pliocene localities of southeastern France. The study of the different parameters show that diagenetic changes are weak. Microstructural features specific to otoliths, such as needle-like crystals and growth increments, are usually well preserved. When present, the microstructural modifications remain limited inside each otolith. Except a few pyritic specimens, the only mineral found is aragonite like in recent specimens. The chemical compositions of fossil and recent otoliths are not significantly different, and any element is preferentially changed by diagenesis. The isotopic composition does not show strong alterations. However, the difference in 18 O content between recent fishes having different ecological habits is not found with the same magnitude in fossil specimens. Finally, when elemental and isotopic compositions are compared, the specimens are sorted according to taxonomy and not according to their geologic age. This suggests that biogenic signals have been preserved.

Comparison of the soluble organic matrices of healthy and diseased shells of Pinctada margaritifera (L.) and Pecten maximus L. (Mollusca, Bivalvia)

Pinctada margaritifera and Pecten maximus are among the mollusks of commercial value. Both are known to show abnormal calcification processes that strongly increase the mortality rate. Several parameters of the soluble organic matrices extracted from the shells of P. margaritifera and P. maximus are analyzed: bulk composition, molecular weights, and acidity. The composition of the matrices of healthy and diseased shells were compared, showing that the protein and the sugar contents are variously modified. Differences between healthy and diseased shells are dissimilar in the two species. This is in accordance with the previously described macroscopic and microscopic alterations (red color, numerous brown membranes). This study does not allow identification the origin of the disease, but provides new insights on the role of sugars in biomineralization processes.

Structure and composition of the aragonitic crossed lamellar layers in six species of Bivalvia and Gastropoda

The microstructures, the chemical composition and the soluble organic matrices of the aragonitic crossed lamellar layers of the shells of six species of molluscs have been studied. The microstructures and chemical contents are similar, whereas the quantities of organic matrices are variable. All the soluble matrices are glycoproteins, with low S contents. Their molecular weights, the protein-sugar ratios and acidities are variable. Neither a gastropod nor a bivalve pattern is recognized. The diversity of the organic matrices probably plays a main role in the fossilization processes of mollusc shells.

Taphonomy and palaeoecology of Olduvai Bed-I (Pleistocence, Tanzania)

Detailed taxonomic and taphomonic studies of rodents and palaeoecological analysis have been undertaken to investigate faunal change in Olduvai Bed-I. The palaeoenvironments inferred from rodent faunas recorded in Olduvai Bed-I suggest a change between the middle (FLK + FLKNN) and the top of the series (FLKN). Changes have also been observed from taxonomic studies of large mammals and from palynological studies. These differences have been attributed in the past to climatic change, but taphonomic studies suggest a more complex scenario. The environment at Olduvai Bed-I is here interpreted through analysis of fossil faunas and fossilization processes. Identification of the causative agents that could have altered the faunal composition provides information on the environment and on the nature of the change observed between the middle and top of Bed-I. This information can then be used to test conflicting hypotheses about the origins and amount of faunal and pollen change. Results show evidence of predation in all units of Bed-I and can be attributed to different predators along the series. Different predator behaviours explain some of the variability observed by previous authors in the small mammal species composition between the middle and the top of Bed-I. After taking taphonomy into account, the remaining faunal differences point to environmental differences between middle and upper Bed-I and even greater within the upper Bed-I sequence. These differences go beyond the range that is present today in the tropical woodland-savanna biome. Our interpretation of the palaeoenvironments is that the middle Bed-I faunas indicate a very rich closed woodland environment, richer than any part of the present-day savanna biome in Africa, changing to less rich woodland in upper Bed-I with a trend towards more open and seasonal woodlands at the top of the series.

Isoelectric properties of the soluble matrices in relation to the chemical composition of some Scleractinian skeletons

Soluble matrices of four Scleractinian skeletons (Madrepora, Favia, Leptastrea and Fungia), were extracted and studied by isoelectric focusing (IEF). The main part of the extracted matrices is acidic. IEF gels are poorly stained or unstained by Coomassie Blue and silver. The positive Alcian Blue staining is indicative of a sulfated and acidic nature of the glycoproteins. Chemical analysis shows high S contents in Scleractinian skeletons. These results are supported by the comparison with IEF and chemical contents of Molluscan shells.