Cristaria Plicata Research Articles

Highly Flexible, High-Performance, and Stretchable Piezoelectric Sensor Based on a Hierarchical Droplet-Shaped Ceramics with Enhanced Damage Tolerance.

Stretchable self-powered sensors are of significant interest in next-generation wearable electronics. However, current strategies for creating stretchable piezoelectric sensors based on piezoelectric polymers or 0-3 piezoelectric composites face several challenges such as low piezoelectric activity, low sensitivity, and poor durability. In this paper, a biomimetic soft-rigid hybrid strategy is used to construct a new form of highly flexible, high-performance, and stretchable piezoelectric sensor. Inspired by the hinged bivalve Cristaria plicata, hierarchical droplet-shaped ceramics are manufactured and used as rigid components, where computational models indicate that the unique arched curved surface and rounded corners of this bionic structure can alleviate stress concentrations. To ensure electrical connectivity of the piezoelectric phase during stretching, a patterned liquid metal acts as a soft circuit and a silicone polymer with optimized wettability and stretchability serves as a soft component that forms a strong mechanical interlock with the hierarchical ceramics. The novel sensor design exhibits excellent sensitivity and durability, where the open circuit voltage remains stable after 5000 stretching cycles at 60% strain and 5000 twisting cycles at 180°. To demonstrate its potential in heathcare applications, this new stretchable sensor is successfully used for wireless gesture recognition and assessing the progression of knee osteoarthritis.

GST-Mu of Cristaria plicata is regulated by Nrf2/Keap1 pathway in detoxification microcystin and has antioxidant function

Glutathione S-transferase is a crucial phase II metabolic enzyme involved in detoxification and metabolism in aquatic organisms. This study aimed to investigate the regulation of Nrf2/Keap1 pathway on microcystin-induced CpGST-Mu expression and CpGST-Mu resistance to hydrogen peroxide. A mu class GST from Cristaria plicata (CpGST-Mu) was identified. The full-length cDNA was 1026 bp, with an open reading frame of 558 bp. Subcellular localization revealed that CpGST-Mu was localized in cytoplasm. The optimum pH and temperature for the catalytic activity of CpGST-Mu protein was pH 6 and 40 °C, respectively. The results of Real-time quantitative PCR showed that CpGST-Mu mRNA was constitutively expressed in tissues, with the highest expression level in hepatopancreas and the lowest expression level in gill. The mRNA level of CpGST-Mu was significantly increased under the stress of microcystins and hydrogen peroxide. CpGST-Mu had an antagonistic effect on hydrogen peroxide. In the knockdown experiments, the mRNA levels of CpGST-Mu exhibited corresponding changes while Nrf2 and Keap1 genes were individually knocked down. These findings indicated that GST-Mu exhibited antioxidant properties and its expression was regulated by Nrf2/Keap1 signaling pathway. The study provided new information on the function of GST-Mu and could contribute to future studies on how to excrete microcystins in molluscs.

Nuclear factor E2-associated factor 2 and musculoaponeurotic fibrosarcoma K mediate regulation glutathione peroxidase of Cristaria plicata after microcystin-induced oxidative stress

Nuclear factor E2-associated factor 2 (Nrf2)/Antioxidant Response Element (ARE) signaling pathway is an endogenous antioxidant pathway that protects cells from oxidative damage. This pathway is triggered when aquatic organisms are exposed to environmental toxicants. In this study, CpMafK (musculoaponeurotic fibrosarcoma K of Cristaria plicata) mRNA expression in hepatopancreas and gills were up regulated after Cristaria plicata (C. plicata) was exposed to microcystin (MC), which showed that CpMafK protected C. plicata from MC. After MC treatment and CpNrf2 (Nrf2 of Cristaria plicata) knockdown, the mRNA expression of CpMafK was down regulated. After MC treatment and CpMafK knockdown, the mRNA expression of CpNrf2 was down regulated. Indicating that the expression of CpNrf2 was positively correlated with CpMafK. CpGPx (GPx of Cristaria plicata) mRNA was also down regulated with the down regulation of CpMafK and CpNrf2. CpGPx promoter contains a variety of transcription factor binding sites, including Nrf2, ARE elements, etc. Gel blocking experiments showed that CpNrf2/CpMafK heterodimers were bound to CpGPx promoters in vitro. Dual luciferase reporter assay showed that CpNrf2/CpMafK heterodimer negatively regulated CpGPx promoter in cells. In conclusion, Nrf2 and MafK mediate regulation of GPx play a crucial role in protecting bivalves from MC.

JNK regulates the Nrf2/NQO1-ARE pathway against Microcystins-Induced oxidative stress in freshwater mussel Cristaria plicata

In response to stress, cells can utilize several processes, such as the activation of the Nrf2/Keap1 pathway as a critical regulator of oxidative stress to protect against oxidative damage. C-Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinase (MAPK) family, is involved in regulating the NF-E2-related nuclear factor 2 (Nrf2)/antioxidant response element (ARE) signaling pathway. NAD(P)H quinone redox enzyme-1 (NQO1), a downstream target gene of the Nrf2 pathway, plays a vital role in removing peroxide and providing resistance to oxidative injury. We found that microcystins (MCs) stimulated CpNrf2 to express and increase anti-oxidative enzyme activities in a previous experiment. In our current study, the full-length cDNAs of JNK and NQO1 from Cristaria plicata (designated CpJNK and CpNQO1) were cloned. The relative levels of CpJNK and CpNQO1 were high in hepatopancreas. Upon MCs induction, the relative level of CpNQO1 was increased, whereas that of CpJNK was decreased significantly. In contrast, CpNrf2 knockdown upregulated the expression of CpJNK mRNA and phosphorylation of CpJNK protein (Cpp-JNK), but inhibited CpNQO1 expression. Additionally, we found that JNK inhibitor SP600125 stimulated expression of CpNQO1 and CpNrf2 upon exposure to MCs, and we further confirmed that CpNrf2 protein combined with the ARE element in CpNQO1 gene promoter in vitro, and increased CpNQO1-ARE-luciferase activity in a CpNrf2-dependent manner. These findings indicated C. plicata effectively alleviated MC-induced oxidative injury through JNK participated in regulating the Nrf2/NQO1-ARE pathway.

A review of the endangered mollusks transcriptome under the threatened species initiative of Korea.

Transcriptome studies for conservation of endangered mollusks is a proactive approach towards managing threats and uncertainties facing these species in natural environments. The population of these species is declining due to habitat destruction, illicit wildlife trade, and global climate change. These activities risk the free movement of species across the wild landscape, loss of breeding grounds, and restrictions in displaying the physiological attributes so crucial for faunal welfare. Gastropods face the most negative ecological effects and have been enlisted under Korea's protective species consortium based on their population dynamics in the last few years. Moreover, with the genetic resources restricted for such species, conservation by informed planning is not possible. This review provides insights into the activities under the threatened species initiative of Korea with special reference to the transcriptome assemblies of endangered mollusks. The gastropods such as Ellobium chinense, Aegista chejuensis, Aegista quelpartensis, Incilaria fruhstorferi, Koreanohadra kurodana, Satsuma myomphala, and Clithon retropictus have been represented. Moreover, the transcriptome summary of bivalve Cristaria plicata and Caenogastropoda Charonia lampas sauliae is also discussed. Sequencing, de novo assembly, and annotation identified transcripts or homologs for the species and, based on an understanding of the biochemical and molecular pathways, were ascribed to predictive gene function. Mining for simple sequence repeats from the transcriptome have successfully assisted genetic polymorphism studies. A comparison of the transcriptome scheme of Korean endangered mollusks with the genomic resources of other endangered mollusks have been discussed with homologies and analogies for dictating future research.

The Anodontini of Vietnam (Mollusca: Bivalvia: Unionidae: Unioninae) with the Description of a New Species

The basic knowledge of freshwater bivalves in the Unionida in some regions of the world is still limited, hindering potential conservation efforts, including in Vietnam. A subset of these mussels, the freshwater bivalve tribe Anodontini, is especially difficult to properly identify morphologically due to intraspecific shell similarity. This study aims to define the species of Anodontini in Vietnam and describe their evolutionary relationships and distributions by estimating phylogenies and analyzing collected specimens. The Anodontini are represented in Vietnam by five species divided among three genera: Sinanodonta, Cristaria, and Pletholophus. Sinanodonta woodiana, a large species complex, is represented in Vietnam by Sinanodonta jourdyi. Cristaria is confirmed to include the widespread Cristaria plicata and substantiates the validity of Cristaria truncata. Finally, Pletholophus is here recognized as distinct from Cristaria, containing two species in Vietnam, Pletholophus tenuis, and a species new to science. Our study is an important baseline for future studies on Vietnamese freshwater mussels and highlights the importance of surveys, molecular work, and taxonomic expertise to describe the biodiversity of understudied regions.

Bioaccumulation and Health Risk Assessment of Metals in Small-Sized Fish (Rhodeus sinensis, Ctenogobius giurinus) and Mussel (Cristaria plicata) from a River Reservoir, Southwest China.

In order to assess the bioaccumulation and health risk of metals in a river reservoir, concentrations of copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) in the water, sediments, two small-sized fish, and a freshwater mussel from the Zhoubai reservoir were examined. The results indicated that all of these metals conform with class one of environmental quality standards for surface water (State Environmental Protection Administration of China, GB 3838-2002). There were no significant differences for total metal concentrations in sediment between the three sampling sites (p > 0.05), but the bioavailable concentrations in S3 were the lowest. The Cd was dominated with exchangeable fraction and showed considerable risk. All metal concentrations except for Pb in Rhodeus sinensis were significantly higher than those in Ctenogobius giurinus (p < 0.05). The metal concentrations in Cristaria plicata showed a similar pattern of bioavailable metals in sediment, indicating that the metal concentrations in aquatic organisms were determined by the bioavailable forms of metals. Negative correlations were observed between the size of fish and concentrations of Cu, Zn, Pb, Cd, and As. However, significant positive correlations were found between the size of mussel and concentrations of Cd (p < 0.01), As (p < 0.05), and Hg (p < 0.01). Zn had the highest BCF values in fish and mussel. The aquatic organisms showed lower ability of metal bioaccumulation from the sediment. Low values of target hazard quotient (THQ), hazard index (HI), and carcinogenic risk (CR) indicated that these metals do not pose a health risk to public through fish and mussel consumption in this study area.

The combined effects of filter-feeding bivalves (Cristaria plicata) and submerged macrophytes (Hydrilla verticillate) on phytoplankton assemblages in nutrient-enriched freshwater mesocosms.

Freshwater ecosystems are threatened by eutrophication, which causes persistent and harmful algal blooms. Filter-feeding bivalve mollusks and submerged macrophytes (SMs) alleviate the eutrophication effects by inhibiting phytoplankton biomass blooms. However, very little is known about whether and how the combined manipulation of filter-feeding bivalves and SMs control eutrophication and influence phytoplankton assemblages. Here, we performed a nutrient-enriched freshwater mesocosm experiment to assess the combined effects of the filter-feeding bivalve Cristaria plicata, a cockscomb pearl mussel, and the macrophyte Hydrilla verticillate on the biomass and composition of phytoplankton assemblages. We found that addition of C. plicata and H. verticillate decreased the water nutrient concentrations and suppressed overall phytoplankton biomass. Further, distinct differences in taxa between restoration and control treatments were observed and noticeably competitive exclusion of cyanobacteria in the restoration treatments occurred. An antagonistic interaction between filter-feeding bivalves and SMs was only detected for total cyanobacteria biomass demonstrating that a larger magnitude of SM restoration may override the effect of filter-feeding bivalves. Our results suggest that manipulation, through the addition of bivalves as grazers, associated with the restoration of SMs, is an efficient approach for reducing cyanobacterial blooms and alleviating eutrophication.

Prx5 of Cristaria plicata has antioxidant function and is regulated by Nrf2/ARE signaling pathway

Cristaria plicata is one of the more important freshwater pearl bivalves in China, which is susceptible to pathogen infection, and greatly impacts the ability of breeding pearls. Nrf2/ARE signaling pathway and its downstream target gene Prx5 have endogenous antioxidant functions to protect cells from oxidative damage. The full-length cDNA of Prx5 was cloned from C. Plicata, which was 1420 bp, encoding a total of 189 amino acids and had two conserved cysteine residues (Cys78 and Cys179). The amino acid sequence of CpPrx5 was highly similar to Prx5 of other species. Real-time fluorescence quantitative PCR showed that CpPrx5 was distributed in various tissues of mussels, and the highest expression was in hepatopancreas. The expression of CpPrx5 up-regulated in hepatopancreas and gills after LPS, PGN and Poly:I:C stimulation. The recombinant plasmid DE3-PGEX-4T-1-CpPrx5 was expressed in Escherichia coli BL21 and showed antioxidant activity. With the increase of CpPrx5 protein concentration, the superhelical form of DNA was protected. The expression of CpPrx5 was up-regulated after interference CpKeap1 and down-regulated after interference CpNrf2. Gel block assay showed that CpNrf2 and CpMafK proteins blocked CpPrx5 promoter. Subcellular localization showed that CpPrx5 was located in 293T nucleus and cytoplasm and CpMafK was located in 293T nucleus. GST-Pull down verified that CpMafK and CpPrx5 could bind in vitro. These results indicated that Prx5 had antioxidant function and could protects DNA from oxidative damage, and participated in transcriptional regulation by combining with the transcription factor MafK. In addition, MafK could combine with Nrf2 to regulate the downstream target gene Prx5.

P62/SQSTM1 upregulates NQO1 transcription via Nrf2/Keap1a signaling pathway to resist microcystins-induced oxidative stress in freshwater mussel Cristaria plicata

Microcystins (MCs) are the most frequent and widely distributed type of cyanotoxin in aquatic systems, and they cause an imbalance of the body's oxidative system. In a previous experiment, we demonstrated that the mollusk Cristaria plicata can protect against MC-induced oxidative damage through the nuclear factor erythroid 2-related factor 2(Nrf2)/Kelch-like epichlorohydrin-related protein-1 (Keap1) pathway. Here, we evaluated whether selective autophagy affects the Nrf2/Keap1a anti-oxidative stress pathway in C. plicata. Full-length cDNA sequences of p62/SQSTM1 from C. plicata (Cpp62) were divided into 2484 bp fragments. From N-terminal to C-terminal, the amino acid sequence of Cpp62 contained PB1 (Phox and Bem1p domain), ZNF (zinc finger domain) chain, LIR (LC3 interacting region) and UBA (ubiquitin-associated domain) domains, but not the KIR (Keap1 interacting region) domain. We confirmed that Cpp62 did not bind to CpKeap1a in vitro, and the relative level of Cpp62 was the highest in the hepatopancreas. Moreover, MCs significantly upregulated the mRNA and protein levels of Cpp62 in the hepatopancreas after CpKeap1a knockdown, whereas Nrf2 upregulated the transcription levels of Cpp62, suggesting that MCs increased Cpp62 expression via the Nrf2/Keap1a signaling pathway. Moreover, Cpp62 and CpNrf2 proteins have a strong affinity for the NQO1 promoter, but MCs inhibited the ability of CpNrf2 and Cpp62 to upregulate luciferase activity. The results show that Nrf2 and the p62 protein induced p62 expression by binding to ARE (antioxidant response element) sequences in the p62 promoter of C. plicata, thereby promoting p62 to resist MC-induced oxidative stress. Therefore, we speculate that MCs induce p62-dependent autophagy in C. plicata, resulting in the inhibition of Nrf2 transcription and Cpp62 promoter activity. These findings help to reveal the mechanism by which the p62-Nrf2/Keap1 pathway mitigates MC-induced oxidative damage in mussels.

Identification of Nrf2/Keap1 pathway and its transcriptional regulation of antioxidant genes after exposure to microcystins in freshwater mussel Cristaria plicata

Microcystins (MC) are one of the most abundant and widely distributed cyanotoxins in aquatic systems. MC inhibits the functions of protein phosphatase 1 and 2A (PP1/2A), which can seriously affect ecosystem integrity. The NF-E2-related nuclear factor 2 (Nrf2)/Kelch-like epichlorohydrin-related protein-1 (Keap1) signaling pathway protects against oxidative damage by activating phase II detoxification/antioxidant enzymes. Our previous study revealed that MC upregulates the expression and enhances the activities of the antioxidant enzymes by stimulating the CpNrf2 signaling pathway. In the current study, to further clarify the regulatory role of Keap1 in response to MC-induced oxidative stress in shellfish, we cloned the full-length cDNA of Keap1a and Keap1b from Cristaria plicata (designated CpKeap1a and CpKeap1b), which are 2952 and 3710 bp peptides, respectively. The amino acid sequence of CpKeap1a and CpKeap1b contained Tram-track and Bric-a-brac (BTB), Intervening region (IVR), and Double glycine repeat (DGR) domain. Additionally, CpKeap1a contained two cysteine residues analogous to Cys-273 and -288 in zebrafish, but CpKeap1b did not. Moreover, CpKeap1a and -1b formed a homodimer and heterodimer, respectively, and also formed a heterodimer with CpNrf2. In the hepatopancreas, the expression levels of CpKeap1a and -1b were the highest, but MC treatment down-regulated the expression of these proteins. Moreover, the transcription of antioxidant enzymes with antioxidant response element (ARE-driven enzymes), including CpMnSOD, CpCu/ZnSOD, CpTRX, CpPrx, CpSe-GPx, and Cpsigma-GST was upregulated by CpNrf2 in the hepatopancreas. Compared with the MC-induced group, CpKeap1a-siRNA1117 injection significantly increased the transcription of mRNAs for ARE-driven enzymes and Nrf2. CpKeap1a-siRNA1117 also enhanced the activities of antioxidation enzymes. These findings demonstrated that Keap1a negatively regulated the expression of Nrf2 protein and MC-induced oxidative stress response in C. plicata. Therefore, we speculated that CpKeap1a promoted CpNrf2 by recognizing and binding MC. These events then protected molluscs from MC-induced oxidative damage.

Comparative analysis of Neptunea cumingii growth, related digestive and immune enzyme indicators, and liver transcriptome under different feeding conditions

Neptunea cumingii is a carnivorous snail with a very high market value, but it cannot be cultivated on a large scale at present due to the lack of an appropriate artificial feed. In this study, we fed N. cumingii four kinds of diets (Cristaria plicata meat, Chlamys farreri mantle, Mytilus edulis meat, and artificial feed) for 90 days and then measured growth indexes and digestive and immune enzyme indexes. We also subjected liver samples to transcriptome sequencing to detect significant differences among the four groups at the transcriptome level. The survival rate of N. cumingii fed with each type of feed was &amp;gt; 90%. The weight, shell length, shell height, and weight gain of the N. cumingii in the C. plicata meat group were significantly higher than those of the other treatment groups, while the values in the artificial feed group were significantly lower than those of the other treatment groups. The superoxide dismutase, catalase, amylase, protease, and lipase activities were higher in the stomach, intestine, and liver of snails in the C. plicata meat feeding group than in those of the other treatment groups, and they were significantly higher than those of the artificial feed group (p &amp;lt; 0.05); the opposite was true for malondialdehyde content. A total of 3407 differentially expressed genes (DEGs) were found in the M. edulis meat group vs. C. plicata meat group comparison. A total of 3422 DEGs genes were identified in the artificial feed group vs. C. plicata meat group comparison. A total of 3,929 DEGs were found in the C. plicata meat group vs. C. farreri mantle group comparison. Through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, we found the DEGs in the liver of N. cumingii fed with the different diets were mainly enriched in the energy metabolism, growth, and immunity pathways. Our results indicated that among the four diets tested, C. plicata meat had the best effect on N. cumingii, and they provided an important reference for identification of suitable diets for the development of N. cumingii artificial breeding.

MAPK/MAK/MRK overlapping kinase mediated apoptosis through caspase signaling pathway from Cristaria plicata

MAPK/MAK/MRK Overlapping Kinase (MOK) belongs to MAP kinase superfamily, which plays an important role in regulating cell growth, division, and differentiation. Caspase-3, as the final executor of apoptosis, has an important position in the caspase-mediated apoptotic signaling pathway. The full-length cDNA of MOK and caspase-3 were cloned from Cristaria plicata (designated CpMOK and CpCaspase-3). The CpMOK gene was sequence with a full-length of 1413 bp, encoding a total of 470 amino acids, and containing an S_TKc structural domain. CpCaspase-3 has a sequence of 2425 bp, encoding 322 amino acids, containing a CASc domain. Real-time fluorescence quantitative PCR analysis showed that CpMOK and CpCaspase-3 distributed in various tissues of C. plicata, and the highest expression of CpMOK and CpCaspase-3 mRNA was in hepatopancreas. The expression of CpMOK was significantly changed in hepatopancreas, gills, and kidneys by the construction of wound model as well as stimulation of LPS, PGN, Poly I: C and Aeromonas hydrophila. Subcellular localization experiments confirmed that CpMOK was localized in the nucleus. Furthermore, the double-stranded RNA (dsRNA) of CpMOK was constructed for interference experiment, and the results showed that the mRNA expression of apoptotic gene signals caspase-1, caspase-3, caspase-7, caspase-8, and caspase-9 were increased. The expression of caspase-1, -3, -7, -9, cytochrome C (Cyt-c) and tumor necrosis factor-α (TNF-α) was detected by ELISA. Fluorescent staining of apoptotic cells using the Tunnel method revealed an increase in the number of apoptotic cells after interference. These results suggested that CpMOK knockdown could induce caspase-mediated apoptosis in C. plicata, and the phosphorylation of the kinase was disrupted during the process.

Distinctive Impact of Heat Treatment on the Mechanical Behavior of Nacreous and Crossed-Lamellar Structures in Biological Shells: Critical Role of Organic Matrix.

As biological ceramic composites, mollusk shells exhibit an excellent strength-toughness combination that should be dependent on aragonite/organic matrix interfaces. The mechanical properties and fracture mechanisms of the nacreous structure in the Cristaria plicata (C. plicata) shell and crossed-lamellar structures in the Cymbiola nobilis (C. nobilis) shell were investigated, focusing on the critical role of the organic matrix/aragonite interface bonding that can be adjusted by heat treatments. It is found that heat treatments have a negative impact on the fracture behavior of the nacreous structure in the C. plicata shell, and both the bending and shear properties decrease with increasing heat-treatment temperature because of the loss of water and organic matrix. In contrast, for the crossed-lamellar structure in C. nobilis shell, the water loss in heat treatment slightly decreases its bending properties. When the organic matrix is melted after an appropriate heat treatment at 300°C for 15 min, its bending properties can be greatly enhanced; in this case, remarkable toughening mechanisms involving crack deflection and the fiber pull-out are exhibited, although the interfacial bonding strength reduces. Therefore, an appropriate heat treatment would bring about a positive impact on the fracture behavior of crossed-lamellar structure in the C. nobilis shell. The major research findings have provided an important inspiration that the inducement of moderately weak interfaces rather than all strong interfaces might enhance the comprehensive mechanical properties of fiber-reinforced ceramic composites.

A high-strength and high-toughness nacreous structure in a deep-sea Nautilus shell: Critical role of platelet geometry and organic matrix

To explore the differences in mechanical behavior of nacre between shells that live in different water depths, the microstructures, phase composition and related mechanical properties of nacre under indentation, three-point bending and shear tests in deep-sea Nautilus and freshwater Cristaria plicata shells were systematically investigated. It is found that the nacreous structure in Nautilus shell exhibits an outstanding combination of high strength and high toughness compared with that in C. plicata shell, attributing to its larger aspect ratio of platelet and interfacial shear resistance. Specifically, the interfacial resistance is mainly generated from the adhesion of organic matrix and friction caused by nano-asperities on platelet surfaces. According to the interfacial resistance model, the stiction force originated from organic matrix adhesion is sensitive to its content, and the friction force produced by nano-asperities presents a positive correlation with their distribution density and dimension. Hence, the higher content of organic matrix of nacre with denser and larger nano-asperities on platelet surfaces in Nautilus shell contributes to a higher interfacial resistance. Therefore, it is the coupled effects of platelet geometries (i.e. aspect ratio and nano-asperity) and organic matrix that result in the high-strength and high-toughness nacreous structure in Nautilus shell, which is thus more conductive to inhabit in the deep sea with extremely high pressure. The present research findings are expected to provide beneficial references for the design of strong and tough nacre-inspired materials with appropriate platelet geometry and content of soft phase.

Bioaccumulation and human health risk assessment of trace metals in the freshwater mussel Cristaria plicata in Dongting Lake, China

Trace metal contamination in water and bioaccumulation in aquatic organisms are human health risks of increasing concern. However, the bioaccumulation of trace metals in the organs of the mussel Cristaria plicata in Dongting Lake, China and the human health risks of mussel consumption are largely unknown. We investigated the concentrations of 15 trace metals and metalloids in surface water, sediments, and C. plicata organs (foot, gill, mantle, and visceral mass) and quantified the bioaccumulation and human health risk of these trace metals in specimens collected from Dongting Lake. The concentrations of most metals in surface water exceeded previously published background values. In contrast, the concentrations of most metals in sediments showed a decreasing trend. Overall, the metal concentrations in the gill and visceral masses of C. plicata were higher than those in the foot and mantle, and higher bioaccumulation capacities were observed for essential metals than for nonessential metals. The mean concentrations of the trace elements Zn, Pb, Cd, As, Cu, and Cr in C. plicata foot samples were lower than the threshold values established by international and Chinese organizations. The estimated daily intake (EDI) values of the essential metal Mn in C. plicata foot was higher than the recommended tolerable daily intake (TDI) values for juveniles. Only Mn for juveniles and As for both juveniles and adults may pose noncarcinogenic health risks through foot consumption. The hazard index (HI) values for adults and juveniles were higher than 1, suggesting significant risks of noncarcinogenic effects to humans by exposure to multiple metals.

Application of crushed shells Cristaria plicata to separation cadmium and chromium from polluted water by static sorption

Cristaria plicata is a species of freshwater mollusk in the genus Cristaria of the family Unionidae. Cristaria plicata shells are available natural raw materials in Vietnam for the production of sorbents that can absorb many pollutants from wastewater. The most important pollutants are heavy metals. The aim of the study was to study the possibility of using powders from Cristaria plicata shells to purify contaminated water from heavy metals such as Cd and Cr by sorption method. A technology for obtaining a sorbent has been developed. After collection, the shells were washed, dried and ground to a size of no more than 0.5 mm, then the powder was soaked in distilled water for 10 hours, dried to a constant weight and sieved through sieves, collecting a fraction with a particle size of about 0.5 mm. Microscopic studies showed that the sorbent parti-cles from the shells of Cristaria plicata contained pores with a diameter of 4.5 to 8.2 microns and a length of 15.9 to 27.6 microns. The static sorption method was used. The Cd and Cr content in water samples before and after sorption was performed by atomic absorption spectrophotometry. It is shown that the sorbent from the shell material of Cristaria plicata can be used quite effectively for wastewater treatment from Cd and Cr. It was found that with an increase in the mass fraction of the powder in the treated water, the concentration of Cr and Cd in this water noticeably decreases. The Cr content drops by 29.5-45.5% after shaking for 60 minutes, while the Cd content drops by 91.6-96.9%. The absorption capacity of the sorbent from the shells of Cristaria plicata depends on the initial concentrations of Cr and Cd, the higher the initial concentration, the more pollutants are absorbed by the sorbent. The best effect of sorption purification is observed at the initial concentrations of Cd 1 mg/l and Cr 20 mg/l. For maximum Cd allocation, the recommended processing time is 40÷60 minutes, and for Cr-80÷100 minutes.

First freshwater mussel-associated piscicolid leech from East Asia

Parasites and symbionts of freshwater mussels are poorly understood, although a diverse assemblage of mussel-associated leeches (Glossiphoniidae) was recently described. Here, we report on the discovery of a fish leech (Piscicolidae) in the mantle cavity of the freshwater mussel Cristaria plicata (Unionidae) in the Russian Far East. It is the first member of this leech family being associated with freshwater molluscs. This leech does not match any known genus and species both morphologically and genetically, and is described here as Alexandrobdella makhrovigen. & sp. nov. It uses mussels as shelter (and probably as a secondary host), while the Amur catfish Silurus asotus (Siluridae) seems to be the primary host. These novel findings indicate that mussel-associated leech assemblage contains at least one piscicolid species. Our fossil-calibrated phylogeny suggests that the crown group of Piscicolidae was originated in the Early Cretaceous. This primarily marine family shares at least five independent colonization events into freshwater environments.

Effect of microcystin on the expression of Nrf2 and its downstream antioxidant genes from Cristaria plicata

Microcystin (MC) is a cyclic heptapeptide toxin. Nuclear factor erythocyte 2-related factor 2 (Nrf2) can enhance cellular survival by mediating phase 2 detoxification and antioxidant genes. In this study, CpNrf2 cDNA sequences were cloned from freshwater bivalve Cristaria plicata. The full-length CpNrf2 cDNA sequence was 4259 bp, and its homology was the highest with Mizuhopecten yessoensis, reaching 46%. CpNrf2 transcription levels were examined in all tested tissues, and the highest level was in hepatopancreas from C. plicata. The recombinant protein pET32-CpNrf2 was purified with the content of 1.375 mg/mL. The expression levels of CpNrf2 mRNA were raised in hepatopancreas after MC stimulation. After CpNrf2 knockdown, CpNrf2 mRNA levels were significantly down-regulated after 24 h. Compared with control group, the expression levels of ARE-driven enzymes (CpMnSOD, CpCuZnSOD, CpTRX, CpPrx, CpSe-GPx and Cpsigma-GST) were significantly increased, and those enzyme activities were also significantly up-regulated in MC-stimulated group. However, in CpNrf2-iRNA group, they were significantly down-regulated. The results revealed that Nrf2/ARE pathway is very crucial to protect molluscs from MC.

Thickness-dependent mechanical properties of nacre in Cristaria plicata shell: Critical role of interfaces

The thickness dependence of mechanical properties of nacre in Cristaria plicata shell was studied under three-point bending tests. The results show that the mechanical behavior of nacre exhibits a strong thickness dependence. The bending strength firstly increases with the increase of specimen thickness and then becomes roughly constant as the thickness reaches a certain value of ∼2.5 mm. However, the mean value of work per unit volume increases constantly with increasing specimen thickness; meanwhile, the cracking mode changes from penetration into the platelets to deflection along the interfaces. The theoretical analyses indicate that the thickness-dependent mechanical properties of nacre are mainly caused by the variation in the number of inter-lamellar interfaces. The more the number of inter-lamellar interfaces is, the higher the strength and work of fracture of nacre under bending tests will be. However, as the number of inter-lamellar interfaces reaches a certain value (e.g., in the present specimen with 2.5 mm thickness), the strength tends to remain constant, while the work of fracture still increases. Therefore, the present research findings are expected to provide a valuable guidance for the interfacial design of nacre-like materials with high strength and toughness.