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Biological modulation of element incorporation presents a major hurdle in the interpretation of geochemical data as an environmental proxy, detailed understanding and quantitative evaluation of the mechanism of elemental fractionation both being essential for reliable reconstruction of an environment. Biogenic calcium carbonate has a specific skeletal microstructure, which is strongly controlled by biomineralization. Since primary processes are more likely reflected on a smaller spatial scale, elemental distribution patterns associated with skeletal microstructure should provide unique information on biological elemental fluctuations, which cannot be determined from large-scale analysis. To study elemental fractionation mechanisms, microscale elemental distribution patterns have been studied in coral skeletons and bivalve and foraminiferal shells and the skeletal microstructure, sulfur distribution, and organic features compared. The microanalytical studies revealed two characteristic patterns that were common to all studied biogenic calcium carbonates, even though the specimens examined represented different phyla: (1) significant compositional heterogeneities that could not be explained by changes in the ambient environment and (2) a strong correlation of “metal/Ca” ratios with all or some of sulfur distribution, skeletal microstructure, and organic character. Based on these common features, I propose a mechanism of elemental fractionation, commonly applicable to biogenic calcium carbonates and involving both composition and/or concentration of organics in the calcifying fluid, that facilitates preferential elemental incorporation into biogenic calcium carbonate.

Three facultative anaerobe mesophilic bacteria were isolated from marine sediment collected off Niigata, Japan. Sequencing of complete 16S ribosomal DNA revealed 99% homology with , , and . Phylogenetic analyses suggest novel strain status thus new strains were designated as strain Hiro-1, strain Hiro-2, and strain Hiro-3. Minimum inhibitory concentration assays using increasing concentrations of NaTeO revealed resistance of strain Hiro-1 at 15 mM, and strain Hiro-2 and strain Hiro-3 both showed resistance at 4 mM. Transmission electron microscopy revealed intracellular aggregation of metallic tellurium nanorods with a minimum unit size of 60-nm nanoparticle.

Calcium oxalate crystals (COC) are one of the most prevalent and widely distributed biomineralizations in plants. The aim of this work is to analyze and compare the data previously reported about the presence and production of COC in leaves of plant species from forests, wetlands, and agroecosystems of the southeast of the Pampean Plain. Diaphanization, clearing of tissues with 50% sodium hypochlorite, and cross sectioning of the leaves were realized. The material was mounted with gelatin–glycerin, and COC were identified and described with optical, polarization, and scanning electron microscopes. Crystal size and density were calculated. Calcification mainly occurred in leaf mesophyll. In terrestrial species, crystals were closely associated with vascular bundles, while in aquatic species, they were associated with aerenchyma. Druses, prisms, and raphides were observed in the leaves of all species analyzed. Average crystal size was smaller in terrestrial species than aquatic ones (12 and 80 μm, respectively), but average crystal density was higher (246 and 23 crystals/mm, respectively). These different patterns in COC production and distribution may be related to taxonomical characteristics, the types of cells where crystals precipitate, their function, and the differential transpiration rates, among other factors.

Biomineralizations are biogenic composites, crystalline or amorphous, produced by the metabolic activity of organisms distributed all over the world. The aim of this work was to evaluate the presence of iron and calcium biomineralizations and their influence in the physicochemical and mineralochemical variations in paleo and actual pedosedimentary sequences of the coastal plains in Mar Chiquita. The complex interaction of calcium with iron biomineralizations, as framboidal and poliframboidal pyrites associated with gypsum, barite, calcite, halite, and iron oxyhydroxides, have demonstrated the active and complex biogeochemistry that occurs in the temperate–wet paleoesturaries and estuaries of the coastal Pampean Plains.Particularly the consequences that different human activities could have, such as the possible acidification processes as result of the iron sulfide oxidation.

The mollusc shell comprises a small amount of organic macromolecules, mostly proteins and polysaccharides, which, all together, constitute the skeletal organic matrix (SOM). In the recent years, the study of the SOM of about two dozens of mollusc species via transcriptomics and/or proteomics has led to the identification of hundreds of shell-associated proteins. This rapidly growing set of data allows several comparisons, shedding light on similarities and differences at the primary structure level and on some peculiar evolutionary mechanisms that may have affected SOM proteins. In addition, it constitutes a prerequisite for investigating the SOM repertoires of sub-fossils or fossil specimens, closely related to known extant species, in order to revisit diagenetic processes, i.e. how SOM proteins degrade during fossilization. These two aspects are briefly exemplified here: on the one hand, , the sea hare, exhibits a vestigial internal shell that has kept a proteomic signature similar to that found in fully functional external shells. On the other hand, subfossil specimens of the giant clam , collected in French Polynesia, precisely dated and analysed by proteomics for their SOM content, comprise several preserved proteins that can still be identified by their peptide signature, in spite of information losses likely due to diagenetic transformations.

Shelk2, a novel shell matrix protein from the Pacific oyster, , is reported to be involved in shell biosynthesis of the prismatic layer. Results of RNAi experiment on showed that Shelk2 has a key role in shell regeneration. When dsRNA of was injected into the adductor muscle of Pacific oyster, the prismatic layer did not grow normally during shell regeneration. Observation of regenerated shell using scanning electron microscopy (SEM) revealed that the size of each column in the prismatic layer was reduced, and the edge of the column top looked rounder. From these results, it was deduced that the columns were less tightly bound with each other than in normally regenerated shells. Furthermore, the surface of the column appeared to be rough. Unexpectedly, the expression level of mRNA was not reduced but remarkably enhanced by the knockdown experiment. Further experiments including gene and protein expression will be necessary for a better understanding of its function and role in oyster shell regeneration.

The “nacro-prismatic” shells are the most studied mollusks, and they are often said to be “the” model to unravel the biomineralization mechanisms. Nevertheless, the nacro-prismatic structure is not unique, despite most data are provided by only three genera. The aragonitic nacre is taxon dependent: in cephalopods and gastropods, nacre is columnar, whereas bivalves have a spiral or sheet nacre. The inner structure of gastropod and cephalopod columnar nacre differs. The shape of the tablets is specific of the taxa. Calcitic and aragonitic prisms exist. The composition of the organic matrices extracted from calcitic prisms with a similar shape and mineralogy strongly differs. The inner structure of aragonite prisms is complex, with a central zone and divergent elongated crystallites at the periphery. Additionally, the relationships between nacre and prisms are also taxonomically related. From these data, whatever the scale at which they are studied, every component of the “nacro-prismatic” model – nacre, prisms, and prism–nacre topographic relations – is highly variable, so that this “model” does not exist; it is a structure.

Recent imaging methods applied to the growing edge of the shell allow for a better appreciation of ancient structural data. Growth of the shell (both lateral extension and thickness increase) is a coordinated mechanism involving a series of clearly identified steps in contrast to the prevailing concept of a direct “self-assembly” process.

In the current method of pearl production, the mantle fragment of a donor pearl oyster is transplanted into a host pearl oyster together with an inorganic bead (pearl nucleus). After this surgical procedure, only outer epithelial cells (OEC) in the transplanted mantle survive in a host pearl oyster and form a pearl sac to begin pearl formation. Therefore, implantation of only the OEC instead of the mantle fragment would be a possible alternative to the current procedure. To examine the potential of pearl production by implanting OEC in , we developed a cell implantation method using the pearl nucleus carrying a small pit inoculated with OEC. As a result, approximately 70% of the inserted nuclei formed the nacreous layer when the OEC were inoculated at 5 × 10 cells/nucleus. Then, OEC isolated from two genetically different types of pearl oysters that significantly differed in shell nacre color (yellowness) were mixed at four different ratios, and the prepared OEC mixtures were transplanted to investigate the effects of the blend on the yellowness of pearls to be harvested. The yellowness of harvested pearls differed significantly in accordance with the mixing ratio. Similarly, OEC isolated from two types of pearl oysters that showed a significant difference in the thickness of their shell nacre aragonite tablets were mixed at four different ratios and transplanted. Mean thickness of the aragonite tablets of the harvested pearls differed according to mixing ratio. These results suggest the method to control pearl quality by blending OEC obtained from pearl oysters genetically improved by selective breeding for traits related to pearl quality.

The bivalve hinge ligament is the hard tissue that functions to open and close shells. The ligament contains fibrous structures consisting of aragonite crystals surrounded by a dense organic matrix. This organic matrix may contribute to the formation of fibrous aragonite crystals, but the mechanism underlying this formation remains unclear. Recently, we showed that tissue inhibitor of metalloproteinase (TIMP) and matrix metalloproteinase (MMP) is related to the formation of the ligament in . BLAST search of genome database revealed that seven MMP genes are encoded in the genome of . To identify the specific MMP that may contribute to ligament formation, the expression level of each MMP was measured in the mantle isthmus, which secretes the ligament. The expression of MMP54089 increased after scratching of the ligament, while the expressions of other MMPs did not increase after doing the same operation. To identify the role of MMP54089 in forming the ligament structure, double-stranded (ds) RNA targeting MMP54089 was injected into the living to suppress the function of MMP54089. Scanning electron microscopic images showed disordered growing surfaces of the ligament in individuals injected with MMP54089-specific dsRNA. These results suggest that PfTIMP and MMP54089 play important roles in the formation of the fibrous ligament structure.