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Cadmium (Cd) is a toxic heavy metal that, when present as a pollutant in the marine environment, is readily accumulated by marine bivalves, causing oxidative stress and tissue damage. This study explored whether short-term depuration could reverse Cd2+-induced toxicity in the ovary of the clam Meretrix meretrix. Clams exposed to 3 mg L-1 Cd2+ for three days showed increased accumulated Cd2+ in their ovaries with obvious tissue damage as shown by loose structure and some apoptotic cells compared with non-exposed clams. Increased oxidative stress in the ovarian tissue was also obvious, as revealed by increased levels of oxidative indicators such as reactive oxygen species (ROS), malondialdehyde (MDA), DNA-protein crosslinking (DPC), and protein carbonylation (PCO) and increased expression levels of genes related to oxidative stress and apoptosis, which included the Bax, Bcl-2, caspase-3, HO-1, Hsp70, NQO1, Nrf2, and MT genes. When the clams were exposed to Cd2+ for three more days, the accumulated Cd2+ level in the ovary increased to more than 10-fold the level in the control clams, accompanied by more severe damage and cell death as well as oxidative stress. However, when the initial three-day Cd2+ exposure was followed by three days of depuration in Cd2+-free seawater, the Cd2+ level in the ovary was reduced by as much as 20%, accompanied by some recovery of tissue damage and reduced oxidative stress, suggesting that short-term depuration may mitigate Cd2+-induced toxicity in M. meretrix, allowing the clams to recover and potentially reducing the risk of Cd2+ exposure from consuming contaminated clams. [ABSTRACT FROM AUTHOR]

C-type lectins (CTLs) are a kind of Ca2+-dependent immunoreactive factors, which participated in pathogens recognition and defense. The present study identified a new CTL from hard clam Meretrix meretrix (designated as MmCTL4). The full-length of MmCTL4 cDNA was 608 bp, encoding a presumed signal peptide of 19 bp and a carbohydrate recognition domain (CRD) of 131 bp. The tertiary structure of recombinant MmCTL4 protein (rMmCTL4) was the typical long double-ring structure with three conserved disulfide bonds, and the motifs in Ca2+-binding sites of MmCTL4 were QPN and WSD. The SYBR Green real-time PCR analysis indicated that MmCTL4 was widely expressed in the hemocytes, hepatopancreas and mantle of healthy clams. After Vibrio splendidus stimulation, the temporal expression profile of MmCTL4 mRNA in hemocytes and hepatopancreas increased by 7.8-fold at 6 hpi and 3.9-fold at 12 hpi, respectively. The cDNA fragments encoding MmCTL4 were recombined into pET-32a (+) vectors, and transformed into Escherichia coli BL21 (DE3). The rMmCTL4 with the presence of Ca2+ performed obvious hemagglutination activity, and could agglutinate E. coli , Bacillus subtilis , and Staphylococcus aureus , while it only weakly agglutinate Vibrio parahaemolyticus and fungi P. pastoris. The agglutination activity of rMmCTL4 were significantly inhibited by D-mannose, D-xylose, D-lactose, maltose and lipopolysaccharides. These results indicated that MmCTL4, as a class of typical pattern recognition receptors (PRRs), could protect the host against pathogen invasion in the innate immunity of clams. [Display omitted] • A novel C-type lectin with QPN and WSD motifs was identified in Meretrix meretrix. • MmCTL4 could be strongly induced after Vibrio splendidus stimulation. • The rMmCTL4 exhibited multiple activities in a Ca2+-dependent manner. [ABSTRACT FROM AUTHOR]

Different sources of proteins have various ways for facilitating the gelation process of surimi matrices, leading to the diverse combined effects with transglutaminase (TG). In this study, the effects of two plant proteins, soy protein isolate (SPI) and pea protein isolate (PPI), and two animal non-muscle proteins, egg white protein (EWP) and whey protein isolate (WPI), with TG addition on the gel properties of clam Meretrix meretrix (MM) surimi gels were investigated, and the mechanisms were explored. In the presence of TG, the exogenous protein addition significantly improved (p < 0.05) the gelation process of the MM surimi. The best improvements were obtained with the combination of EWP, where the gel strength, cooking loss, and water holding capacity were enhanced by 113.08%, 67.89%, and 26.30%, respectively. The addition of SPI showed a relatively weak enhancement compared to EWP incorporation, followed by the addition of PPI and WPI. The results of optical microscopy, differential scanning calorimetry, and chemical forces demonstrated that TG preferentially promoted plant proteins to form self-aggregation in the surimi system, and SPI generated more polymers than PPI. In contrast, the interpenetration of animal proteins and MM myofibrillar proteins was improved by TG. EWP formed a double cross-linking network within the MM protein network, while WPI acted as a binder to promote protein-protein interactions. This research could provide novel insights for developing MM resources and establish a theoretical foundation for the use of composite exogenous protein additives to enhance the gel properties of MM surimi products. • Plant/animal proteins could improve the gelation of TG-added MM surimi. • TG generated more polymers between plant proteins within MM gel network. • SPI generated more self-aggregates than PPI in the presence of TG. • The interpenetration of animal proteins with MM surimi was promoted by TG. • TG induced a double cross-linking network between EWP and MM protein. [ABSTRACT FROM AUTHOR]

The effects and mechanisms of four exogenous proteins, soy protein isolate (SPI), pea protein isolate (PPI), egg white protein (EWP), and whey protein isolate (WPI), on the gelation of Meretrix meretrix (MM) surimi were investigated. The exogenous protein addition significantly increased the G* of samples to 1.36-1.60 folds compared to the MM group, and the MM/EWP sample presented a better time-stable structure. Furthermore, the incorporation of SPI and EWP reduced expressible water content by 17.51 % and 21.61 % in MM gel, respectively. Moreover, SPI and PPI interacted with water to act as fillers within the MM matrix, where SPI formed larger self-aggregations than PPI. A double cross-linked network was generated by EWP and MM protein, and WPI increased the interaction with MM protein as a binder. This research could provide a theoretical basis for the processing and utilization of exogenous proteins in MM., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

• Post-stress recovery assays separate Meretrix meretrix into proactive and reactive. • Nano-TiO 2 exposure impaired clams' survival and physiological conditions. • High survival rate in proactive clams might change ecosystem population structure. • Proactive clams had better adaptability under nano-TiO 2 exposure. Nano-TiO 2 is inevitably released into aquatic environment with increasing of nanotechnology industries. Study pointed that different individuality showed divergent behavioral and physiological response when facing environmental stress. However, the effects of nano-TiO 2 on tolerance of bivalves with different individualities remain unknown. In the study, clams were divided into two types of individuality - proactive and reactive by post-stress recovery method. It turned out that proactive individuals had quicker shell opening level, stronger burrowing behavior, faster feeding recovery, higher standard metabolic rate and more rapid ammonia excretion ability than reactive individuals after exposed to air. Then, the survival rate, hemocytes response and oxidase activity of classified clams were evaluated after nano-TiO 2 exposure. Results showed that after 30 d exposure, proactive individuals accelerated burrowing behavior with higher survival rate. Moreover, proactive clams had better adaptability and less hemocytes response and oxidative damage than reactive clams. The study highlights the individualities of marine shell fish determine individual capacity to adapt to environmental changes, play important roles in aquaculture and coastal ecosystem health. [ABSTRACT FROM AUTHOR]

To understand the effect of salinity on the toxicokinetics, oxidative stress, and detoxification of cadmium-exposed Meretrix meretrix , M. meretrix were acclimatized to different salinities (8, 14, 20, 26, and 32 ppt) for 14 d, exposed to 10 μg/L Cd for 7 d, followed by a 28-day depuration period. The internal Cd concentration was determined, and the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST)), and the malondialdehyde (MDA) content were measured. The mRNA expression levels of antioxidant enzyme (Cu/Zn SOD , CAT) and detoxification-related genes metallothionein (MT) were analyzed. The mean concentrations of Cd in M. meretrix tissues were in the order gill > digestive gland > mantle > axe foot. The Cd uptake rate in the four tissues decreased with increasing salinity (range: 14–26 ppt). The Cd elimination half-lives were the highest at 8 ppt and 14 ppt salinity. Cadmium activated the four oxidative stress-related related enzymes in the gills. At the end of accumulation period, Cd exposure at 20 ppt salinity significantly increased the expression of Cu/Zn SOD. CAT expression was significantly inhibited at 20 ppt salinity, but was induced at 32 ppt. MT mRNA expression was only induced under Cd at 20 ppt salinity. At the end of depuration period, Cu/Zn SOD expression was inhibited at salinities of 8, 14, and 26 ppt. The results indicated that SOD, CAT, GST, MDA, Cu/Zn SOD , CAT , and MT were sensitive to cadmium in a water environment, and can be used as indicators of marine heavy metal pollution. [Display omitted] • The Meretrix meretrix were exposed to 10 μg/L Cd at salinities of 8, 14, 20, 26, and 32. • Cd concentration in tissues was: gill > digestive gland > mantle > axe foot. • Cd uptake rates increased inversely with salinity at the range of 14–26. • The oxidative stress related parameters play important roles in oxidative damage protection. • MT plays an important role in Cd detoxification. [ABSTRACT FROM AUTHOR]