Calcium Carbonate Crystals Research Articles

Relative Strength of Polycation Adsorption on Oxide Surfaces.

Polyelectrolyte adsorption onto surfaces is widely employed in water treatment and mining. However, little is known of the relative interaction strengths between surfaces and polymer. This fundamental property is assumed to be dominated by electrostatics, i.e., attractive interactions between opposite charges, which are set by the overall ionic strength ("salt concentration") of the solution, and charge densities of the surface and the polymer. A common, counterintuitive finding is a range of salt concentrations over which the amount of adsorbed polyelectrolyte increases as electrostatic interactions are tempered by the addition of salt. After an adsorption maximum, higher salt concentrations then produce the expected gradual desorption of polyelectrolyte. In this work, the salt response of the adsorption of the same narrow molecular weight distribution polycation, poly(N-methyl-4-vinylpyridinium), PM4VP, to a variety of surfaces was explored. Oxide powders for adsorption included Al2O3, SiO2, Fe2O3, Fe3O4, TiO2, ZnO, and CuO. Planar surfaces included silicon wafers, mica, calcium carbonate, and CaF2 single crystals. The PM4VP was radiolabeled with 14C so that sensitive, submonolayer amounts could be detected. The position of the peak maximum, or the lack of a peak, in response to added salt was used to rank the electrostatic component of the interaction. The importance of charge regulation, a shift in the surface pKa in response to solution species, was highlighted as a mechanism for adsorption on the "wrong" side of the isoelectric point and also as a factor contributing to the difficulty of reaching the totally desorbed state even at the highest salt concentrations.

Microstructural Evolution of Calcium Sulfoaluminate Cement during the Wet-Carbonation Process

Calcium sulfoaluminate (CSA) cement, as a type of low-carbon cement, can contribute to further reduction in carbon emissions with carbonation technologies. However, the detailed microstructure development of CSA cement during the carbonation process has been rarely analyzed. In this paper, wet carbonation was applied to CSA cement to investigate the microstructure evolution of carbonation products and carbon absorption capacity of CSA cement by means of pH measurement, X-ray diffraction (XRD) measurement, thermogravimetric (TG) measurement, Fourier-transformed infrared spectroscopy (FT-IR) measurement and scanning electron microscope measurement. During the carbonation process, the formed ettringite product and the dicalcium silicate clinker were carbonated immediately to generate calcium carbonate crystals, silica gel and aluminum hydroxide (AH3) gel. With the trend of pH increasing first and notably decreasing later, the coupling interaction between the hydration and carbonation reactions of CSA cement was revealed. From the XRD and TG results, three types of calcium carbonate crystal forms (calcite, vaterite and aragonite) were detected, and the content of calcium carbonate increased with the increase in carbonation time. FT-IR analysis further confirmed the existence of calcium carbonate, silica gel and AH3 gel with their characteristic vibrations. Moreover, the microstructure of carbonation products with different morphologies was observed. The application of wet carbonation to CSA cement provides a more comprehensive insight to the carbonation mechanism of this low-carbon cement.

Didymium arenosum, a myxomycete new to science from the confluence of deserts in northwestern China.

A new myxomycete species, Didymium arenosum, was described based on morphological evidence and phylogenetic analyses. The species was discovered in the arid region at the confluence of the Badain Jaran desert and Tengger desert on the leaves of Betula platyphylla and was cultivated in a moist chamber culture. Morphologically, the species is distinguished by the greenish-yellow calcium carbonate crystals on the surface and the spores covered with small warts, some of which are connected into a short line. A phylogenetic analysis of D. arenosum strongly supports its classification as a separate clade. The spore to spore agar culture of D. arenosum requires 23 days, and this study provides a detailed description of its life cycle.

Surface Treatment of Rammed Earth Heritage Sites Using MICP Technology: An Investigation of Rainwater Erosion Resistance via Indoor Experiments and In Situ Testing

Rammed earth, a commonly used building material in ancient times, differs from natural sedimentary layers in that it is more compact. Buildings constructed from historical rammed earth sites frequently encounter the issue of rainwater erosion. Microbially induced calcium carbonate precipitation (MICP) is commonly applied to sand soil treatment, yet reports on its use for stabilizing rammed earth are scarce. This study focused on the rammed earth of the Shanhaiguan Great Wall and explored the efficacy of MICP in mitigating rain erosion through permeation tests, splash experiments, and scouring trials. The findings indicate that the forms of rain erosion damage under MICP treatment vary across different operational conditions. In laboratory experiments, as the concentration of the cementation solution increases, the amount of calcium carbonate crystals also increases. However, the permeability, splash resistance, and rain erosion resistance initially increase and then decrease. When the cementation solution concentration is 1.0 mol/L, the penetration rate is the highest, lasting 712.55 s. The splash pit rate is the lowest, at only 1.2 mm, and the soil erosion rate is the lowest, at only 4.13%. The rain erosion resistance in the field test exhibit the same trend, and the optimal concentration is 1.2 mol/L. The optimal concentration mechanism involves the aggregation of calcium carbonate crystals at suitable cementation solution concentrations, which begin to fill the soil particle pores, effectively resisting rainwater erosion. At lower concentrations of the cementation solution, calcium carbonate crystals are merely adsorbed by soil particles without blocking the pores. Due to the high compressibility of rammed earth, which results in lower porosity, a higher concentration of the cementation solution leads to rapid pore clogging by excessive calcium carbonate crystals, which accumulate on the surface to form a white crust layer. The MICP technique can effectively alleviate rainwater erosion in rammed earth, and the optimal concentration needs to be tailored to the porosity of the rammed earth. This mechanism was also validated in field scouring experiments on the Shanhaiguan Great Wall’s rammed earth.

Purification of Produced Water from a Sour Oilfield in South Kuwait. 2. Oil-Water Separation and Crystallization of Calcium Carbonate

Purification of Produced Water from a Sour Oilfield in South Kuwait. 2. Oil-Water Separation and Crystallization of Calcium Carbonate

Project M: investigating the effect of additives on calcium carbonate crystallisation through a school citizen science program

Crystallisation pathways of calcium carbonate are strongly influenced by the presence of additives. Through X-ray diffraction, samples made by the Project M Scientists reveal the effect of amino acid and related additives on the crystal structures of calcite and vaterite.

Systematic comparisons of preparative protocols to generate various types of stone-related crystals for in vitro study of renal calculi

In vitro studies of stone-related crystals and crystals-cell interactions have been extensively done to investigate cellular, molecular and pathogenic mechanisms leading to renal calculi. Effective preparation of various types of stone-related crystals is thus crucial for such studies. Nevertheless, various protocols for preparing these stone-related crystals were scatteredly reported without comparative analysis of their efficacies and yields. Herein, we systematically compared our protocols (with the suffix “-Si”) for preparing calcium oxalate (CaOx) monohydrate (COM), CaOx dihydrate (COD), magnesium ammonium phosphate (struvite), uric acid (UA), calcium phosphate dihydrate (brushite), hydroxyapatite (HAP), and calcium carbonate (CaCO3) crystals with other protocols published previously. The morphological evaluation revealed that our protocols provided the most homogeneous and most typical monoclinic prismatic, bipyramidal, coffin lid and rectangle shapes of COM, COD, struvite and UA crystals, respectively. There were comparable morphological results for brushite, HAP and CaCO3 crystals generated by different protocols. Our protocols provided the greatest yield for generating brushite crystals but with lower yields for others. Chemical analysis by Fourier transform infrared (FTIR) spectroscopy revealed comparable results among different protocols to generate each crystal type. In summary, all these protocols can be used to generate each crystal type. But our protocols offer the best quality, in terms of homogeneity and typical shape, for generating COM, COD, struvite and UA crystals.

Triaxial compression test of MICP sand column and simulation of failure process

Microbially induced calcium carbonate precipitation (MICP) technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regulation of environmental factors MICP can be used as a cementing agent to cement cohesionless sand particles to form the materials with the characteristics of higher strength, better durability and environmental friendliness, as well as a good engineering application prospect. In this paper, the shear strength of sand column was tested by triaxial compression tests, and the strength index was obtained. In order to further study the micro-strength mechanism and the failure process, based on the discrete element method, a numerical model of MICP cemented sand column was established considering the factors of matrix soil particle gradation, particle morphology, content ratio of induced calcium carbonate, pore distribution characteristics, inter-particle cementation and so on. The failure process of MICP cemented sand column under load was analysed by numerical simulation, and the reliability of the numerical model was tested by combining with the stress intensity curve of samples under test conditions. The results indicate that compared with the actual triaxial tests of MICP cemented sand column, although there are deviations in stress and strain, cohesion and internal friction angle, the numerical simulation shows similar development law and intensity amplitude, and the same failure trend. The work in this paper verifies the reliability of the numerical model and provides a theoretical basis for the subsequent analysis of the factors influencing the geotechnical mechanical properties of biomineralized materials.

Unveiling the Carbonation Behavior and Microstructural Changes of Magnesium Slag at 0 ℃

Magnesium slag (MS) is an industrial byproduct with high CO2 sequestration potential. This study investigates the carbonation behavior and microstructural changes of MS during wet carbonation at 0 °C. XRD, TG, FTIR, SEM, and BET techniques were used to characterize the phase composition, microstructure, and porosity of MS samples carbonated for different durations. The results showed that the main carbonation products were calcite, vaterite, and highly polymerized silica gel, with particle sizes around 1 μm. The low-temperature environment retarded the carbonation reaction rate and affected the morphology and crystallization of calcium carbonate. After 480 min of carbonation, the specific surface area and porosity of MS increased substantially by 740% and 144.6%, respectively, indicating improved reactivity. The microstructure of carbonated MS became denser with calcite particles surrounded by silica gel. This study demonstrates that wet carbonation of MS at 0 °C significantly enhances its properties, creating an ultrafine supplementary cementitious material with considerable CO2 sequestration capacity.

Induced crystallization for the simultaneous removal of hardness-iron–manganese in groundwater: An experimental study

Hardness, iron, and manganese are common groundwater pollutants, that frequently surpass the established discharge standard concentrations. They can be effectively removed, however, through induced crystallization. This study has investigated the effectiveness of the simultaneous removal of hardness-iron-manganese and the crystallization kinetics of calcium carbonate during co-crystallization using an automatic potentiometric titrator. The impacts pH, dissolved oxygen (DO), and ion concentration on the removal efficiency of iron and manganese and their influence on calcium carbonate induced crystallization were assessed. The results suggest that pH exerts the most significant influence during the removal of hardness, iron, and manganese, followed by DO, and then the concentration of iron and manganese ions. The rate of calcium carbonate crystallization increased with pH, stabilizing at a maximum of 10−10 m/s. Iron and manganese can be reduced from an initial level of 4 mg/L to <0.3 mg/L and 0.1 mg/L, respectively. The removal rate of iron, however, was notably higher than that of manganese. The DO concentration correlates positively with the removal of iron and manganese but has minimal impact on the calcium carbonate crystallization process. During the removal of iron and manganese, competitive interactions occur with the substrate, as increases in the concentration of one ion will inhibit the removal rate of the other. Characterization of post-reaction particles and mechanistic analysis reveals that calcium is removed through the crystallization of CaCO3, while most iron is removed through precipitation as Fe2O3 and FeOOH. Manganese is removed via two mechanisms, crystallization of manganese oxide (MnO2/Mn2O3) and precipitation. Overall, this research studies the removal efficiency of coexisting ions, the crystallization rate of calcium carbonate, and the mechanism of simultaneous removal, and provides valuable data to aid in the development of new removal techniques for coexisting ions.

Competition between homogeneous and heterogeneous crystallization of CaCO3 during water softening

Homogeneous and heterogeneous crystallization of CaCO3 simultaneously occur in seed-induced crystallization during water softening, while suppressing homogeneous crystallization is necessary due to the production of fine particulates that poorly precipitate. However, homogeneous crystallization is difficult to distinguish from heterogeneous crystallization. Consequently, a central focus in improving water softening is understanding their competing activities. In this study, a novel method for distinguishing homogeneous and heterogeneous calcium carbonate crystallization is described that utilizes magnetite as seed particles. Results showed that saturation index (SI) was the primary driver of both homogeneous and heterogeneous crystallizations. Heterogeneous crystallization was preferentially promoted at low SI, while homogeneous crystallization was promoted at high SI. The highest suppression effect to homogeneous crystallization occurred at SI of about 1.01. Seed dosage and mean particle size were the primary parameters related to the competition of the crystallization types. Higher seed dosage and smaller seed particle sizes promoted heterogeneous crystallization and suppressed homogeneous crystallization. Due to the good adaptability of heterogeneous crystallization at low SI, the absorption of CO2 from the air into the solutions also improved the efficiency of hardness removal. The introduction of seed particles did not change crystalline product phases, with calcite being the only observed phase and possessing rhombohedral forms with highly regular and smooth edges. Water softening pilot test results showed that SI of 1.5 was more favorite for CaCO3 layer formation on seed surface and hardness removal in comparison with SI of 1.0 and 2.0. Overall, the results from this study demonstrate that the introduction of seed particles is a promising approach to suppress the homogeneous crystallization of CaCO3. Moreover, these results can serve as a framework for improved seed-induced crystallization during water softening.

Micro-macro investigation on bio-cemented sand under different grouting saturation: An effective enhancement method

Microbial-induced calcium carbonate precipitation (MICP) is a new biotechnology that can be used to improve the strength of soils. Unsaturated soils are common in nature and saturation is a significant factor affecting the efficiency of bio-cementation. This study investigated the properties of MICP under different grouting saturation conditions. Unconfined compressive strength (UCS) tests confirmed that biocemented sand could get higher strength under unsaturated grouting conditions with the same calcium carbonate content which helps reduce the material cost. Scanning electron microscopy (SEM) test results show that at lower saturation, the size and amount of calcium carbonate crystals were insufficient but calcium carbonate mainly gathered between the particles. At higher saturation, larger calcium carbonate crystals were produced and exited in pores and on the particle surface, increasing the filling effect. Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) test results show that the dominant calcium carbonate morphology detected in samples was calcite, which was the most stable one. X-ray computed tomography (CT) test results show that after cementation, the measured contact surface area became uniform and the coordination number was higher. The flow direction of bacteria and the cementing solution did not induce significant anisotropy in the cementation process. The effective cementation and content of calcium carbonate jointly influenced the improvement of soil mechanical properties.

Enrichment, characterization, and sand consolidation application of urease active calcite-producing bacteria.

Minerals such as calcium carbonate, which is prevalent in marble and limestone, are present naturally in rocks. Both physicochemical processes and microbial processes can result in the creation of calcium carbonate in nature, as is well documented. In this study, microbiologically induced calcite precipitation potential of three different Travertine-type water sources (Pamukkale Travertine Spring (PTS), Pamukkale Travertine Terraces (PTT), and Red Travertine of Karahayit (RTK)) using three different incubation media (NB, NB3, and ATCC1832) were investigated. After enrichment with ATCC1832 media, urease assays were positive for all of the microbial sources. The PTS and PTT were cultured with ATCC1832 medium for 48h, which showed the best results for urease activity and microbial growth among other samples. Metagenome analyses indicated that PTT enriched with ATCC1832 media contains > 99% Firmicutes, while PTS enriched with ATCC1832 contains > 99% Proteobacteria at the Phylum level. Results from SEM-EDX and XRD analysis revealed that calcite and/or vaterite were the minerals that emerged from the mineralization of the PTS and PTT during incubation. The type of calcium carbonate crystals tended to change from one form to another when the incubation period extends from 72 to 120h. Both the PTS and the PTT were able to precipitate calcite within the sand column. However, the bacteria from the PTT (26% CaCO3) outperformed those from the PTS (18% CaCO3) in terms of calcium carbonate deposition on the 21st day of incubation.

Calcium carbonate polymorph selection in fish otoliths: A key role of phosphorylation of Starmaker-like protein

Fish otoliths are calcium carbonate biominerals found in the inner ear commonly used for tracking fish biochronologies and as a model system for biomineralization. The process of fish otolith formation is biologically controlled by numerous biomacromolecules which not only affect crystal size, shape, mechanical properties, but also selection of calcium carbonate polymorph (e.g., aragonite, vaterite). The proteinaceous control over calcium carbonate polymorph selection occurs in many other species (e.g., corals, mollusks, echinoderms) but the exact mechanism of protein interactions with calcium and carbonate ions – constituents of CaCO3 – are not fully elucidated. Herein, we focus on a native Starmaker-like protein isolated from vaterite asteriscus otoliths from Cyprinus carpio. The proteomic studies show the presence of the phosphorylated protein in vaterite otoliths. In a series of in vitro mineralization experiments with Starmaker-like, we show that native phosphorylation is a crucial determinant for the selection of a crystal's polymorphic form. This is the first report showing that the switch in calcium carbonate phase depends on the phosphorylation pattern of a single isolated protein. Statement of SignificanceCalcium carbonate has numerous applications in industry and medicine. However, we still do not understand the mechanism of biologically driven polymorph selection which results in specific biomineral properties. Previous work on calcium carbonate biominerals showed that either several macromolecular factors or high magnesium concentration (non-physiological) are required for proper polymorph selection (e.g., in mollusk shells, corals and otoliths). In this work, we showed for the first time that protein phosphorylation is a crucial factor for controlling the calcium carbonate crystal phase. This is important because a single protein from the otolith organic matrix could switch between polymorphs depending on the phosphorylation level. It seems that protein post-translational modifications (native, not artificial) are more important for biomolecular control of crystal growth than previously considered.

Generation of Multiple Concentration Gradients Using a Two-Dimensional Pyramid Array.

Concentration heterogeneity of diffusible reactants is a prevalent phenomenon in biochemical processes, requiring the generation of concentration gradients for the relevant experiments. In this study, we present a high-density pyramid array microfluidic network for the effective and precise generation of multiple concentration gradients. The complex gradient distribution in the 2D array can be adaptively adjusted by modulating the reactant velocities and concentrations at the inlets. In addition, the unique design of each reaction chamber and mixing block in the array ensures uniform concentrations within each chamber during dynamic changes, enabling large-scale reactions with low reactant volumes. Through detailed numerical simulation of mass transport within the complex microchannel networks, the proposed method allows researchers to determine the desired number of reaction chambers within a given concentration range based on experimental requirements and to quickly obtain the operating conditions with the help of machine learning-based prediction. The effectiveness in generating a multiple concentration gradient environment was further demonstrated by concentration-dependent calcium carbonate crystallization experiments. This device provides a highly efficient mixing and adaptable concentration platform that is well suited for high-throughput and multiplexed reactions.

Inhibition of calcium carbonate nucleation and crystallization by carboxymethyl dextran: Experiments and molecular dynamics simulations

Fouling causes huge economic losses for industrial process. In this work, experimental and molecular dynamics simulation approaches were used to carefully examine the scale inhibitory effects of carboxymethyl dextran (CMD) on the nucleation and crystallization process of calcium carbonate. The findings of the experiment demonstrated that CMD could significantly inhibit calcium carbonate's crystallization and nucleation processes. Moreover, an increase in the CMD concentration prolonged the induction period of calcium carbonate nucleation, and led to an increase in the critical conductivity value, inhibition effect on the nucleation process, and scale inhibition efficiency. The simulation results demonstrated the presence of strong interactions between the calcium ions in solution and the carboxyl groups of CMD. The probability and strength of calcium and carbonate ions adsorbing to the solution's surface decreased as the CMD concentration rose. Adsorption probability and strength of calcium and carbonate ions in the solution declined as CMD concentration rose, tightly agglomerated calcium carbonate gradually dispersed into small clusters and ions, and scale inhibition effectiveness improved. The experimental results were found to be in good agreement with the simulation results.

Carboxylic acid-induced freshwater acidification effects on behavior and operculum ultrastructure in the gastropod mollusc Bellamya bengalensis

ABSTRACT Global freshwater acidification, accelerated by rising pCO2, remains a critical ecological concern. Despite the prevalence of carboxylic acids like acetic acid (AA) and benzoic acid (BA) in freshwater, their potential to exacerbate acidification and impact biota is not fully understood. In this study, we examined behavioural disruptions during acute exposures (96 h) and operculum ultrastructure changes during chronic exposures (28 days) to ecologically-relevant concentrations of AA (39.7, 79.5, and 99.4 mg/L) and BA (31.4, 62.8, and 78.5 mg/L) in Bellamya bengalensis. Acute exposures revealed significant behavioural disruption, including reduced activity and impaired escape behaviour. Chronic exposures led to ultrastructural defects in the operculum, with more pronounced effects in BA-exposed groups. Acidification scenarios appeared to impact calcium carbonate crystal formation, compromising opercula structure. Our study underscores the importance of understanding both acute and chronic effects of freshwater acidification on molluscan species, emphasising the need for further research into the underlying mechanisms and thresholds of acidification tolerance.

Calcium Carbonate Precipitation Behavior in the System Ca-Me2+-CO3-H2O (Me2+ = Co, Ni, Cu, Fe): Ion Incorporation, Effect of Temperature and Aging

Crystalline calcium carbonates (CCCs) are among the most widespread minerals on the Earth’s surface and play a crucial role in the global carbon cycle, heavy metal sorption and incorporation. Among the numerous factors that influence the precipitation of CCCs from solution, the most determinant are the presence of additives in the mineral-forming medium, temperature, and crystallization time (aging time). The current work fills the gaps in the study of calcium carbonate crystallization from heavy metal (Me2+ = Co, Ni, Cu Fe)-containing solutions (Me2+/Ca 0.005–1.600) at different temperatures (3 and 23 °C) and aging times (21–158 days). The resulting precipitates were studied using optical and scanning electron microscopy, powder X-ray diffraction and energy-dispersive X-ray spectroscopy. Three crystalline calcium carbonates (synthetic analogues of calcite, aragonite and monohydrocalcite), as well as amorphous carbonate (AC), were found in the resulting precipitates. Temperature and aging time have a considerable effect on the phase composition, morphology and heavy metal content in CCCs. Low temperature (3 °C) and short aging times are generally favorable for the formation of monohydrocalcite and amorphous carbonate, while calcite tends to form at a higher temperature (23 °C) and in long-term experiments. Heavy metals can be incorporated into the calcite/monohydrocalcite crystal lattice in sufficient amounts, while aragonite can host a very small amount of Me2+ (or none). Calcite can concentrate Co (up to ~0.25 atoms per formula unit (apfu)) and Ni/Cu (up to ~0.05 apfu), while its Fe content is very close to the detection limits. Calcite precipitated at a higher Me2+/Ca ratio and temperature (23 °C) contains less Me2+ compared to calcite precipitated at a lower Me2+/Ca ratio and temperature (3 °C). Monohydrocalcite can host up to ~0.1 apfu of Co/Ni/Cu with no detectable preference for Me2+. The amount of Me2+ in monohydrocalcite decreases as aging time or temperature increases. It is worth noting that AC is the main carrier of heavy metals in the system being investigated and it should be considered the main host phase in heavy metal adsorption from aqueous solutions. The results obtained can be used to solve environmental issues and in mineral resource management.

Experimental study on the effect of cementation curing time on MICP bio-cemented tailings

Tailings dam break and leakage accidents usually threaten the safety of people around the mining area. In addition, tailings leakage seriously pollutes the surrounding environment. In view of the above problems, the tailing sand is solidified based on the microbial induced calcite precipitation (MICP). This method can not only enhance the strength of tailing sand, but also solidify heavy metals in tailings. In order to optimize the curing time of MICP bio-cemented tailings, improve the strength and cost-effectiveness, this study used the layered injection method to cement the tailings. Combined with the unconfined compressive strength, calcium carbonate content and heavy metal leaching effect of MICP bio-cemented tailings, the effect of MICP curing time on bio-cemented tailings was analyzed. The results showed that the curing time of MICP bio-cemented tailings has a great influence on the strength of tailings, and has little effect on the fixation of heavy metals in tailings. The curing time of the optimized MICP biocemented tailings is 10 days. The unconfined compressive strength of the MICP bio-cemented tailing sand specimen is 1.01 MPa. When the cementation curing time is greater than 10 d, the cementation curing time will no longer be the main factor affecting the MICP bio-cemented tailings. After the MICP bio-cemented tailings samples were leached for 5 days, the fixation rates of Pb2+, Zn2+, total Fe, Mn2+, Cu2+, Cd2+ and total Cr in the leaching solution were 100%, 100%, 100%, 94.80–98.45%, 100%, 100%, 93.34–95.56%, respectively. The results of FTIR, XRD, SEM and EDS showed that when the tailings were cemented and solidified many times the cementation liquid metabolized by Sporosarcina pasteurii was mainly used for the growth of existing calcium carbonate crystals rather than the formation of new calcium carbonate crystals. The deposition of these larger calcium carbonate crystals can stably fill the gaps between the tailings particles, cement the tailings particles together and improve the strength of the tailings.

Core genes of biomineralization and cis-regulatory long non-coding RNA regulate shell growth in bivalves

IntroductionBivalve molluscs are abundant in marine and freshwater systems and contribute essential ecosystem services. They are characterized by an exuberant diversity of biomineralized shells and typically have two symmetric valves (a.k.a shells), but oysters (Ostreidae), some clams (Anomiidae and Chamidae) and scallops (Pectinida) have two asymmetrical valves. Predicting and modelling the likely consequences of ocean acidification on bivalve survival, biodiversity and aquaculture makes understanding shell biomineralization and its regulation a priority. ObjectivesThis study aimed to a) exploit the atypical asymmetric shell growth of some bivalves and through comparative analysis of the genome and transcriptome pinpoint candidate biomineralization-related genes and regulatory long non-coding RNAs (LncRNAs) and b) demonstrate their roles in regulating shell biomineralization/growth. MethodsMeta-analysis of genomes, de novo generated mantle transcriptomes or transcriptomes and proteomes from public databases for six asymmetric to symmetric bivalve species was used to identify biomineralization-related genes. Bioinformatics filtering uncovered genes and regulatory modules characteristic of bivalves with asymmetric shells and identified candidate biomineralization-related genes and lncRNAs with a biased expression in asymmetric valves. A shell regrowth model in oyster and gene silencing experiments, were used to characterize candidate gene function. ResultsShell matrix genes with asymmetric expression in the mantle of the two valves were identified and unique cis-regulatory lncRNA modules characterized in Ostreidae. LncRNAs that regulate the expression of the tissue inhibitor of metalloproteinases gene family (TIMPDR) and of the shell matrix protein domain family (SMPDR) were identified. In vitro and in vivo silencing experiments revealed the candidate genes and lncRNA were associated with divergent shell growth rates and modified the microstructure of calcium carbonate (CaCO3) crystals. ConclusionLncRNAs are putative regulatory factors of the bivalve biomineralization toolbox. In the Ostreidae family of bivalves biomineralization-related genes are cis-regulated by lncRNA and modify the planar growth rate and spatial orientation of crystals in the shell.