Sea Cucumber Apostichopus Japonicus Research Articles

CircRNA8388 functions as the sponge for miR-2392 during intestinal regeneration in sea cucumber Apostichopus japonicus

The sea cucumber Apostichopus japonicus can expel internal organs under stress and regenerate them subsequently. However, growth is delayed during regeneration, significantly impacting the industry. Circular RNAs (circRNAs) are single-stranded circular RNA molecules produced through alternative splicing of mRNA precursors. They play crucial roles in regulating gene expression via the ceRNA mechanism. In this study, circRNA profiles of control and regenerated intestines were constructed. A total of 15,874 circRNAs were identified, with a length of 300‐350 nucleotides (nt) being the most abundant. Sanger sequencing confirmed the circular structure of circRNA398. Compared with the normal intestine, 50 and 83 differentially expressed circRNAs (DE-circRNAs) were identified in the regenerated intestine at 1 and 3 days post evisceration (dpe), respectively. Gene ontology (GO) terms for signal transduction and development regulation were most significantly enriched in 1dpeVScon and 3dpeVScon treatments, respectively. The dual-luciferase assay revealed that circRNA8388 functions as a sponge for miR-2392, participating in the remodeling of the extracellular matrix (ECM). In conclusion, these findings will contribute to the enhancement of the non-coding RNA database for echinoderms and lay the groundwork for future investigations into circRNA regulation during intestinal regeneration.

Evidence of size-dependent toxicity of polystyrene nano- and microplastics in sea cucumber Apostichopus japonicus (Selenka, 1867) during the intestinal regeneration

Microplastics are ubiquitous pollutants in the global marine environment. However, few studies have adequately explored the different toxic mechanisms of microplastics (MPs) and nanoplastics (NPs) in aquatic organisms. The sea cucumber, Apostichopus japonicus, is a key organism in the marine benthic ecosystem due to its crucial roles in biogeochemical cycles and food web. This study investigated the bioaccumulation and adverse effects of polystyrene micro- and nanoplastics (PS-M/NPs) of different sizes (20 μm, 1 μm and 80 nm) in the regenerated intestine of A. japonicus using multi-omics analysis. The results showed that after 30-day exposure at the concentration of 0.1 mg L−1, PS-MPs and PS-NPs accumulated to 155.41–175.04 μg g−1 and 337.95 μg g−1, respectively. This excessive accumulation led to increased levels of antioxidases (SOD, CAT, GPx and T-AOC) and reduced activities of immune enzymes (AKP, ACP and T-NOS), indicating oxidative damage and compromised immunity in the regenerated intestine. PS-NPs had more profound negative impacts on cell proliferation and differentiation compared to PS-MPs. Transcriptomic analysis revealed that PS-NPs primarily affected pathways related to cellular components, e.g., ribosome, and oxidative phosphorylation. In comparison, PS-MPs had greater influences on actin-related organization and organic compound metabolism. In the PS-M/NPs-treated groups, differentially expressed metabolites were mainly amino acids, fatty acids, glycerol phospholipid, and purine nucleosides. Additionally, microbial community reconstruction in the regenerated intestine was severely disrupted by the presence of PS-M/NPs. In the PS-NPs group, Burkholderiaceae abundance significantly increased while Rhodobacteraceae abundance decreased. Correlation analyses demonstrated that intestinal regeneration of A. japonicus was closely linked to its enteric microorganisms. These microbiota-host interactions were notably affected by different PS-M/NPs, with PS-NPs exposure causing the most remarkable disruption of mutual symbiosis. The multi-omic approaches used here provide novel insights into the size-dependent toxicity of PS-M/NPs and highlight their detrimental effects on invertebrates in M/NPs-polluted marine benthic ecosystems.

Shelter Capacity of Artificial Reefs for Sea Cucumber Apostichopus japonicas Is Influenced by Water Flow and Food Resources in Laboratory Experiments

Artificial reefs have been advocated and implemented as management tools for aquaculture, species conservation and habitat replacement. However, the shelter capacity of artificial reefs and its influencing factors are still not well understood. In this study, we identified factors that may limit the shelter capacity of artificial reefs for sea cucumber (Apostichopus japonicas) with a laboratory experiment. We investigated how water flow and food availability affect the shelter capacity and conducted shelter utilization experiments to determine whether sea cucumber sheltering behavior was density dependent. The results revealed that shelter capacity of artificial reefs in high velocity is significantly higher than that of artificial reefs in low velocity or no velocity. The artificial reefs that were provided food had significantly higher shelter capacity than those that did not have food. The densities did not affect the sheltering capacity of artificial reefs in the laboratory experiment. There was a logarithmic relationship between the shelter capacity and shelter availability assessed by the exposed surface area of the artificial reefs. In conclusion, abundant food resources and high water flow may have a positive effect on the shelter capacity of artificial reefs.

Dietary tryptophan effectively decreases the behavioral impacts of handling stresses on the sea cucumber Apostichopus japonicas

Dietary tryptophan effectively decreases the behavioral impacts of handling stresses on the sea cucumber Apostichopus japonicas

Neuronal cell populations in circumoral nerve ring of sea cucumber Apostichopus japonicus: Ultrastructure and transcriptional profile

The echinoderm nervous system has been studied as a model for understanding the evolution of the chordate nervous system. Neuronal cells are essential groups that release a ‘cocktail’ of messenger molecules providing a spectrum of biological actions in the nervous system. Among echinoderms, most evidence on neuronal cell types has been obtained from starfish and sea urchin. In sea cucumbers, most research has focused on the location of neuronal cells, whereas their transcriptional features have rarely been investigated. Here, we observed the ultrastructure of neuronal cells in the sea cucumber, Apostichopus japonicus. The transcriptional profile of neuronal cells from the circumoral nerve ring (CNR) was investigated using single-cell RNA sequencing (scRNA-seq), and a total of six neuronal cell types were identified. 26 neuropeptide precursor genes (NPPs) and 28 G-protein-coupled receptors (GPCR) were expressed in the six neuronal cell types, comprising five NPP/NP-GPCR pairs. Unsupervised pseudotime analysis of neuronal cells showed their different differentiation status. We also located the neuronal cells in the CNR by immunofluorescence (IF) and identified the potential hub genes of key cell populations. This broad resource serves as a valuable support in the development of cell-specific markers for accurate cell-type identification in sea cucumbers. It also contributes to facilitating comparison across species, providing a deeper understanding of the evolutionary processes of neuronal cells.

Potential sexual pheromones of sea cucumber Apostichopus japonicus and their functions on aggregative and spawning behavior

The surging market demand for sea cucumbers (Apostichopus japonicus) has fueled a thriving growth in the sea cucumber breeding industry. Pheromones are molecules that evolve signals in defined proportions in the case of multicomponent pheromones, emitted by one individual and received by a second individual of the same species to cause a specific response. It remains an enigma as to how the species of sea cucumber, devoid of visual, auditory, and olfactory senses, aggregate and communicate within their groups, as well as coordinate gamete release during the breeding period. We hypothesize that pheromones may serve as the medium for facilitating these behaviors and propose conducting experiments centered around pheromonal investigation. In this study, we aimed to analyze common metabolites of male A. japonicus using LC-MS/MS technology and bioinformatics. Coelomic fluid and ejaculate fluid were analyzed, with aquaculture water serving as the control. Eight target pheromones were analyzed, and eight of metabolite analogs were tested for aggregation and spawning behaviors. Results showed that β-sitosterol at a concentration of 10 μg·L−1 significantly promoted aggregation (21.25 % average rate) and induced a significant increase in spawning rate (58 %) of A. japonicus. The significance of this study lies in the fact that by collecting and utilizing pheromones of A. japonicus, farmers can accurately determine the reproductive cycle and optimal breeding season for A. japonicus. This enables fish farmers to implement effective breeding management strategies at the appropriate time, thereby increasing the success rate of reproduction and providing valuable technical support for the cultivation of A. japonicus seedlings.

Effects of gut bacterial community on differential growth of sea cucumber (Apostichopus japonicus): Molecular mechanisms based on host-gut microbiome co-metabolism

Gut microbiome and their metabolites are increasingly recognized for their pivotal role in regulating the health and growth of the host. The mechanism by which the host-gut microbiome co-metabolism affects the growth rate of sea cucumber (Apostichopus japonicus) remains unclear. In this study, the intestinal wall tissues of fast-growing (FG) and slow-growing (SG) A. japonicus were collected from the full-sib family for 16S amplicon sequencing, metagenomics, metabolomics, and transcriptomics analyses. The results showed a marked variation in the gut bacterial community of A. japonicus with different growth rates. Compared with SG group, FG A. japonicus had a higher abundance of Bacteroidetes. Many of these bacteria were associated with the degradation of polysaccharides, which could potentially affect growth performance. The abundance of Proteobacteria, however, was found to be higher in SG A. japonicus, thereby increasing the potential risk of disease. The metabolome results were further supported by the predicated KEGG functions of the gut microbiomes, lots of metabolites related to the metabolism and biosynthesis of fructose 6-phosphate, arachidonic acid, oleic acid, and dihydroxyacetone phosphate were upregulated in the FG A. japonicus. Furthermore, the genes (IGF1, HK, PK, PCK1) were significantly upregulated in the FG A. japonicus, which were mainly enriched in the metabolic pathways of lipids, amino acids, and carbohydrates. Gut bacterial community via their unique metabolic pathways, which in turn affected the metabolic phenotypes of the organism and eventually led to differences in growth performance of A. japonicus. These findings might help understand the molecular mechanisms of growth gap in sea cucumber, thereby increasing the mariculture production.

Incorporating physiological knowledge into correlative species distribution models minimizes bias introduced by the choice of calibration area

Correlative species distribution models (SDMs) are important tools to estimate species’ geographic distribution across space and time, but their reliability heavily relies on the availability and quality of occurrence data. Estimations can be biased when occurrences do not fully represent the environmental requirement of a species. We tested to what extent species’ physiological knowledge might influence SDM estimations. Focusing on the Japanese sea cucumber Apostichopus japonicus within the coastal ocean of East Asia, we compiled a comprehensive dataset of occurrence records. We then explored the importance of incorporating physiological knowledge into SDMs by calibrating two types of correlative SDMs: a naïve model that solely depends on environmental correlates, and a physiologically informed model that further incorporates physiological information as priors. We further tested the models’ sensitivity to calibration area choices by fitting them with different buffered areas around known presences. Compared with naïve models, the physiologically informed models successfully captured the negative influence of high temperature on A. japonicus and were less sensitive to the choice of calibration area. The naïve models resulted in more optimistic prediction of the changes of potential distributions under climate change (i.e., larger range expansion and less contraction) than the physiologically informed models. Our findings highlight benefits from incorporating physiological information into correlative SDMs, namely mitigating the uncertainties associated with the choice of calibration area. Given these promising features, we encourage future SDM studies to consider species physiological information where available.

Characterization of the Apoptotic and Antimicrobial Activities of Two Initiator Caspases of Sea Cucumber Apostichopus japonicus.

Caspase (CASP) is a protease family that plays a vital role in apoptosis, development, and immune response. Herein, we reported the identification and characterization of two CASPs, AjCASPX1 and AjCASPX2, from the sea cucumber Apostichopus japonicus, an important aquaculture species. AjCASPX1/2 share similar domain organizations with the vertebrate initiator caspases CASP2/9, including the CARD domain and the p20/p10 subunits with conserved functional motifs. However, compared with human CASP2/9, AjCASPX1/2 possess unique structural features in the linker region between p20 and p10. AjCASPX1, but not AjCASPX2, induced marked apoptosis of human cells by activating CASP3/7. The recombinant proteins of AjCASPX2 and the CARD domain of AjCASPX2 were able to bind to a wide range of bacteria, as well as bacterial cell wall components, and inhibit bacterial growth. AjCASPX1, when expressed in Escherichia coli, was able to kill the host bacteria. Under normal conditions, AjCASPX1 and AjCASPX2 expressions were most abundant in sea cucumber muscle and coelomocytes, respectively. After bacterial infection, both AjCASPX1 and AjCASPX2 expressions were significantly upregulated in sea cucumber tissues and cells. Together, these results indicated that AjCASPX1 and AjCASPX2 were initiator caspases with antimicrobial activity and likely functioned in apoptosis and immune defense against pathogen infection.

Ferroptosis resists intracellular Vibrio splendidus AJ01 mediated by ferroportin in sea cucumber Apostichopus japonicus

Ferroptosis, a kind of programmed cell death, is characterized with iron-dependent lipid ROS buildup, which is considered as an important cellular immunity in resisting intracellular bacterial infection in mammalian macrophages. In this process, lipid ROS oxidizes the bacterial biofilm to inhibit intracellular bacteria. However, the function of ferroptosis in invertebrate remains unknown. In this study, the existence of ferroptosis in Apostichopus japonicus coelomocytes was confirmed, and its antibacterial mechanism was investigated. First, our results indicated that the expression of glutathione peroxidase (AjGPX4) was significantly inhibited by 0.21-fold (p < 0.01) after injecting A. japonicus with the ferroptosis inducer RSL3, and the contents of MDA (3.93-fold, p < 0.01), ferrous iron (1.40-fold, p < 0.01), and lipid ROS (3.10-fold, p < 0.01) were all significantly increased under this condition and simultaneously accompanied with mitochondrial contraction and disappearance of cristae, indicating the existence of ferroptosis in the coelomocytes of A. japonicus. Subsequently, the contents of ferrous iron (1.40-fold, p < 0.05), MDA (2.10-fold, p < 0.01), ROS (1.70-fold, p < 0.01), and lipid ROS (2.50-fold, p < 0.01) were all significantly increased, whereas the mitochondrial membrane potential and GSH/GSSG were markedly decreased by 0.68-fold (p < 0.05) and 0.69-fold (p < 0.01) under Vibrio splendidus (AJ01) infection. This process could be reversed by the iron-chelating agent deferoxamine mesylate, which indicated that AJ01 could induce coelomocytic ferroptosis. Moreover, the results demonstrated that the intracellular AJ01 load was clearly decreased to 0.49-fold (p < 0.05) and 0.06-fold (p < 0.01) after treating coelomocytes with RSL3 and ferrous iron, which indicated that enhanced ferroptosis could inhibit bacterial growth. Finally, subcellular localization demonstrated that ferrous iron efflux protein ferroportin (AjFPN) and intracellular AJ01 were co-localized in coelomocytes. After AjFPN interference (0.58-fold, p < 0.01), the signals of ferrous iron and lipid ROS levels in intracellular AJ01 were significantly reduced by 0.38-fold (p < 0.01) and 0.48-fold (p < 0.01), indicating that AjFPN was an important factor in the introduction of ferroptosis into intracellular bacteria. Overall, our findings indicated that ferroptosis could resist intracellular AJ01 infection via AjFPN. These findings provide a novel defense mechanism for aquatic animals against intracellular bacterial infection.

Importance of the ECM-receptor interaction for adaptive response to hypoxia based on integrated transcription and translation analysis.

Low dissolved oxygen (LO) conditions represent a major environmental challenge to marine life, especially benthic animals. For these organisms, drastic declines in oxygen availability (hypoxic events) can trigger mass mortality events and thus, act as agents of selection influencing the evolution of adaptations. In sea cucumbers, one of the most successful groups of benthic invertebrates, the exposure to hypoxic conditions triggers adaptive adjustments in metabolic rates and behaviour. It is unclear, however, how these adaptive responses are regulated and the genetic mechanisms underpinning them. Here, we addressed this knowledge gap by assessing the genetic regulation (transcription and translation) of hypoxia exposure in the sea cucumber Apostichopus japonicus. Transcriptional and translational gene expression profiles under short- and long-term exposure to low oxygen conditions are tightly associated with extracellular matrix (ECM)-receptor interaction in which laminin and collagen likely have important functions. Finding revealed that genes with a high translational efficiency (TE) had a relatively short upstream open reading frame (uORF) and a high uORF normalized minimal free energy, suggesting that sea cucumbers may respond to hypoxic stress via altered TE. These results provide valuable insights into the regulatory mechanisms that confer adaptive capacity to holothurians to survive oxygen deficiency conditions and may also be used to inform the development of strategies for mitigating the harmful effects of hypoxia on other marine invertebrates facing similar challenges.

Immune responses of sea cucumber (Apostichopus japonicus) to combined environmental stress from high temperature and oil pollution

Context High temperature and oil pollution are typical examples of environmental stress to sea cucumber (Apostichopus japonicus) in northern China. Aims Evaluate the combined effects of high temperature and oil pollution on the immune responses of sea cucumbers. Methods In this study, we investigated the immune responses in the respiratory tree of sea cucumber subjected to the optimal temperature (16°C), high temperature (26°C), Oman crude oil (OCO) water-accommodated fractions (WAF) at 16°C (WAF + 16°C) and OCO WAF at 26°C (WAF + 26°C) for 48 h. Key results All three treatments significantly up-regulated total antioxidant capacity and disturbed active oxygen species homeostasis in sea cucumbers. Moreover, all three treatments caused immune-enzyme activity disorders, manifested by a significant increase in acid–alkaline phosphatase and nitric oxide synthase activities and a noticeable decline in lysozyme activity. Conclusions Combining the integrated biomarker-response index (WAF + 26°C &gt; 26°C &gt; WAF + 16°C), the combined stress could result in a more adverse effect on the immune responses of sea cucumbers than do high temperature or oil pollution alone, which might further exacerbate the health challenges for sea cucumbers in response to environmental stress. Implications This study has provided an insight into the immune impacts in benthic organisms caused by high temperature and oil pollution.

A multi-objective optimization approach for green supply chain network design for the sea cucumber (Apostichopus japonicus) industry

In China, aquatic supply chain network design does not include the green concept or the coordination of environmental and economic performance. Sea cucumber (Apostichopus japonicus) is an aquatic product of high economic value; however, studies on sea cucumber supply chain network optimization are lacking. This study is the first to design the sea cucumber supply chain and construct an optimization model. Considering the characteristics of the sea cucumber industry, LCA for Experts software and the CML-IA-Aug. 2016-world method were used to assess each aquaculture model's global warming potential (GWP), as the environmental performance indicator. In addition, multi-objective genetic algorithm (MOGA) coupled with Modified Technique for Order of Preference by Similarity to Ideal Solution (M-TOPSIS) integrates yield production, economic benefits, and environmental performance. The results demonstrated that cage seed rearing (CSR) combined bottom sowing aquaculture (BSA) represents the best production strategy upstream of the sea cucumber supply chain. In the downstream, the best proportion of sales channels in supermarkets, boutique stores and online shops accounted for 14.79 %, 58.02 % and 27.19 % of the production, respectively. The proposed optimization scenario 4 (S4) can increase product profit by 27.88 % and reduce GWP by 56.89 %. The following improvement measures are proposed: using sea cucumber aquaculture industry standards (cleaner production and green supplier selection) to regulate the behavior of enterprises, adopting an ecological and green production strategy, eliminating high-energy consumption and high emission production practices, and promoting widespread adoption of green consumption concepts. Finally, these measures may improve the sea cucumber supply chain, achieve coordinated environmental and economic performance development in the sea cucumber industry, and provide guidance for green optimization of other aquatic product supply chains in China.

A Novel Frontier in the Geographic Distribution of the Japanese Sea Cucumber Apostichopus japonicus (Selenka, 1867) (Stichopodidae: Holothuroidea) in the World

The natural distribution of the Japanese sea cucumber (Apostichopus japonicus Selenka, 1867), a sea cucumber species, is characterized by the Northwest Pacific. Long-term monitoring studies from 2020 to 2024 document a significant deviation from the known natural distribution of A. japonicus and its ability to extensively colonize the Gulf of Izmit, the easternmost part of the Sea of Marmara. This record is also the first documentation of the species from the Mediterranean Sea. Population data extracted from 67 samples allowed the determination of size and weight distribution, length-weight relationship, and condition factor. The study delves into the implications for fisheries management by evaluating the species’ dispersion beyond its natural range and its adaptation, shedding light on potential threats from illegal hookah diving fisheries. While its presence offers potential economic benefits through fishing income, its emergence as an invasive species can pose critical ecological risks to the receiving ecosystem.

Triterpene Glycosides from the Viscera of Sea Cucumber Apostichopus japonicus with Embryotoxicity.

Sea cucumbers release chemical repellents from their guts when they are in danger from predators or a hostile environment. To investigate the chemical structure of the repellent, we collected and chemically analyzed the viscera of stressed sea cucumbers (Apostichopus japonicus) in the Yellow Sea of China. Two undescribed triterpene glycosides (1 and 2), together with a known cladoloside A (3), were identified and elucidated as 3β-O-{2-O-[β-d-quinovopyranosyl]-4-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-glucopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (1), 3β-O-{2-O-[β-d-glucopyranosyl]-4-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-glucopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (2), 3β-O-{2-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-xylopyranosyl-(1→4)-β-d-quinovopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (3) by spectroscopic analysis, including HR-ESI-MS and NMR spectra. Compounds 1, 2, and 3 display embryonic toxicity, as indicated by their 96-hour post-fertilization lethal concentration (96 hpf-LC50) values of 0.289, 0.536, and 0.091 μM, respectively. Our study discovered a class of triterpene glycoside compounds consisting of an oligosaccharide with four sugar units and a holostane aglycone. These compounds possess embryotoxicity and may serve as chemical defense molecules in marine benthic ecosystems.

Investigation of the Presence of Fibrillin in Sea Cucumber (Apostichopus japonicus) Body Wall by Utilizing Targeted Proteomics and Visualization Strategies.

Fibrillin is an important structural protein in connective tissues. The presence of fibrillin in sea cucumber Apostichopus japonicus is still poorly understood, which limits our understanding of the role of fibrillin in the A. japonicus microstructure. The aim of this study was to clarify the presence of fibrillin in the sea cucumber A. japonicus body wall. Herein, the presence of fibrillin in sea cucumber A. japonicus was investigated by utilizing targeted proteomics and visualization strategies. The contents of three different isoforms of fibrillin with high abundance in A. japonicus were determined to be 0.96, 2.54, and 0.15 μg/g (wet base), respectively. The amino acid sequence of fibrillin (GeneBank number: PIK56741.1) that started at position 631 and ended at position 921 was selected for cloning and expressing antigen. An anti-A. japonicus fibrillin antibody with a titer greater than 1:64 000 was successfully obtained. It was observed that the distribution of fibrillin in the A. japonicus body wall was scattered and dispersed in the form of fibril bundles at the microscale. It further observed that fibrillin was present near collagen fibrils and some entangled outside the collagen fibrils at the nanoscale. Moreover, the stoichiometry of the most dominant collagen and fibrillin molecules in A. japonicus was determined to be approximately 250:1. These results contribute to an understanding of the role of fibrillin in the sea cucumber microstructure.

Transcriptome analysis of sea cucumber (Apostichopus japonicus) in southern China under heat stress

Sea cucumber (Apostichopus japonicus) is a significant aquatic economic species globally. However, the advancement of the sea cucumber aquaculture industry is impeded by its high susceptibility to elevated temperatures. To elucidate the impact of high temperature on physiological changes, gene expression, and metabolic responses in sea cucumbers, we conducted transcriptional profiling of A. japonicus under heat stress. Our results revealed 3691 differentially expressed genes (DEGs), comprising 1629 up-regulated and 2062 down-regulated genes, between the control and treatment groups. Analysis of the Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Ontology (GO), and Protein-Protein Interaction Networks (PPI) indicated that high-temperature stress triggered the expression of stress defense-related genes while inhibiting the expression of genes associated with development and metabolism. Furthermore, 30 out of 39 DEGs were annotated to heat shock protein genes, underscoring the crucial role of these genes in the regulatory mechanism of A. japonicus in response to heat stress. In summary, our findings provide fundamental insights for further investigation into the molecular mechanisms in A. japonicus under high-temperature stress and may contribute to the development of novel strategies for identifying heat-tolerant candidate genes through the analysis of their transcriptional changes in the future.

Evaluation of the chronic toxicity of bisphenol A and bisphenol AF to sea cucumber Apostichopus japonicus after long-term single and combined exposure at environmental relevant concentration

Bisphenols are emerging endocrine disrupting pollutant, and several studies have reported that they are already ubiquitous in various environmental matrices and intend to deposit in sediment. The primary sources of bisphenols are river and sewage discharge. Sea cucumber (Apostichopus japonicus), a typical deposit feeder, is one of the most important commercial marine species in Aisa. However, the effects of the bisphenol A (BPA) and its analogues bisphenol AF (BPAF) on sea cucumber was unclear. In this study, we carried out field survey in major sea cucumber farming areas in northern China, with the aim of determining which bisphenol analogue is the major bisphenol contamination in this aquaculture area. The results showed that the presence of BPAF was detected in four sampling sites (Dalian, Tangshan, Laizhou, and Longpan). The mean level of BPAF in Laizhou sediment samples was the highest which reached to 9.007 ± 4.702 μ g/kg. Among the seawater samples, the BPAF only have been detected in the samples collected at Longpan. (0.011 ± 0.003 μ g/L). Furthermore, we conducted an experiment to evaluate the single and combined toxicity of BPA and BPAF on sea cucumbers. The concentrations were informed by the findings based on the results of field research. (0.1, 1.0, and 10 μ g/L). After exposure, the body weight gain, and specific growth rate showed no significant changes (P > 0.05). We observed the histological alterations in respiratory tree of treated sea cucumbers including the fusion and detachment of lining epithelial tissue, and increase of lumen space. However, the catalase (CAT), malondialdehyde (MDA), and glutathione (GSH) activity was not significantly changed (P > 0.05). We evaluated the effects of BPA and BPAF through calculating the integrated biomarker response index (IBR), and the results indicated that the toxicity of combined treatment was higher than single treatment. Additionally, BPAF exposure to A. japonicus was more toxic than BPA.

A2M possesses anti-bacterial functions by recruiting and enhancing phagocytosis through GRP78 in an echinoderm

Alpha-2-macroglobulin (A2M) is an extracellular macromolecule mainly known for its role as a broad-spectrum protease inhibitor in mammals. However, the immune recognition and regulation mechanisms of A2M in invertebrates are still not well investigated. In the current study, the role of sea cucumber Apostichopus japonicus A2M in the regulation of innate immune responses was explored. We found that AjA2M promotes phagocytosis of Vibrio splendidus in coelomocytes of sea cucumber. Then two major functional structural domains of AjA2M, the thioester domain (TED) and the receptor-binding structural domain (RBD) were cloned. It was found that the AjA2M-TED binds to pathogens while causing Vibrio splendidus aggregation; the AjA2M-RBD interacts with the Glucose Regulated Protein 78 (AjGRP78), subsequently AjGRP78 accelerates the degradation of Vibrio splendidus in lysosomes by facilitating polymerisation and rearrangement of the cytoskeleton. Collectively, the findings together suggest that A2M-GRP78 axis mediates immune signaling pathway of phagocytosis and AjA2M has been characterized to play an essential crucial role in antibacterial immune responses of invertebrates.

Integrated metabolome–metagenome analysis provides new insights into the impacts of sea cucumber (Apostichopus japonicus) aestivation on marine sediment composition

To explore the impacts of sea cucumber aestivation on sediment composition, sediments were sampled from aestivation sites and non-aestivation sites of a commercial Apostichopus japonicus culture pond, and metabolome–metagenome integrated analysis was performed. The results showed that 1) there was no significant difference in the microbial composition of sediments between aestivation and non-aestivation sites, but the relative abundances of some bacterial species changed slightly (especially pathogenic and spoilage species); 2) altered average relative abundances of potential host bacteria of antibiotic resistance genes (ARGs) were observed; 3) compared with non-aestivation site sediments, decreased average absolute abundances of two ARGs (tetW and floR) and increased average absolute abundance of one ARG (tetM) were observed in aestivation site sediments; and 4) a total of 74 significantly differentially expressed metabolites (SDMs) were identified in aestivation sites compared with non-aestivation sites. Four SDMs were closely correlated with antibacterial activity and bacterial physiology. All data observed in this study indicate that sea cucumber aestivation does not affect sediment microbial composition but does influence the relative abundances of some bacteria species; in addition, tetM might be considered a key indicator for monitoring and indicating ARG transfer or the sediment status of sea cucumber culture ponds during aestivation. In conclusion, the observations of this study enrich our knowledge of the impacts of the physiological behavior of marine ecosystem inhabitants on their ecosystem and provide novel insights for the management of aquaculture activities.