Sea Cucumber Apostichopus Japonicus Research Articles

Identification and functional characterization of a novel TRPA1 gene from sea cucumber Apostichopus japonicus and interaction with miR-2013 in response to salt stress.

Salinity is important abiotic factor influencing sea cucumber aquaculture. This study aimed to identify and functional study of a novel transient receptor potential cation channel subfamily A member 1 (TRPA1) involved in salinity stress through interaction with miR-2013 in the sea cucumber. The full-length cDNA sequence was 1369bp in length and encoded 138 amino acids. The TRPA1 homolog protein was a hydrophilic protein without a signal peptide and was predicted to a spatial structure of seven helices and eight random coils and two major ANK functional domains. Bioinformatic analysis and luciferase reporter assays confirmed TRPA1 as a target gene of miR-2013. Quantitative PCR revealed that miR-2013 was induced upregulation after salinity stress, while TRPA1 showed upregulated expression with maximum expression at 24h. The expression of miR-2013 and TRPA1 was negatively regulated. Transfection experiments were conducted to validate the role of miR-2013 and TRPA1 in salinity response. The results showed that miR-2013 was upregulated and TRPA1 was downregulated after transfection with miR-2013 mimics, while miR-2013 was downregulated and TRPA1 was upregulated after transfection with miR-2013 inhibitor. Transfection with si-TRPA1 homolog resulted in upregulation of miR-2013 and downregulation of TRPA1 homolog. These findings suggest that miR-2013 can regulate the expression of TRPA1 under salt stress, and highlight the importance of miR-2013 and TRPA1 in salt stress response. miR-2013 mimics improved the survival rate, while miR-2013 inhibitor and si-TRPA1 reduced it. These findings suggest that miR-2013 and TRPA1 play important roles in sea cucumbers adaptation to salinity changes.

Swing Regulates Movement Direction in the Sea Cucumber Apostichopus japonicus in the Presence of Food Cue: New Insights into Movement Patterns.

Regulating movement direction is essential in the locomotion of animals. Sea cucumbers, as eyeless animals, do not have eyes for the perception of the surrounding environment and food. They have a unique way of swinging their bodies when a food cue is detected, although they lack an important perceptual tool. The present study investigated the movement patterns of the sea cucumber Apostichopus japonicus in the absence of a food cue (experiment 1) and in the presence of a food cue (experiment 2). In experiment 1, we found that the movement of sea cucumbers was close to a linear motion (motion linearity 0.91 ± 0.01). In experiment 2, sea cucumbers most frequently adjusted the movement direction when being exposed to food (84 times/216 min), indicating that sea cucumbers adjusted the direction of movement in the swing state but not the motion state. In experiment 2, we found significantly lower time in the immobility state in the sea cucumbers in the presence of food cues compared to that of those without being exposed to food cues, and the frequency of the motion state in response to food cues was 1.6 times than that of those without food cue. This suggests that food cues cause the change in motion state in sea cucumbers. Swing frequency was 1.7 times higher in sea cucumbers exposed to food cues than that of those not exposed to food cues. Further, sea cucumbers in the presence of food showed significantly better performances in swing angle and swing velocity compared to those not exposed to food cues. This suggests that food cue significantly affects the swing state of sea cucumbers. Notably, the present study described the movement patterns of sea cucumbers when they detected food cues, and other factors (such as the detection of predators) need to be further studied. The present study provides new insights into the regulation of movement direction in eyeless organisms.

Analysis of differentially expressed genes in the sea cucumber Apostichopus japonicus under heat stress

Analysis of differentially expressed genes in the sea cucumber Apostichopus japonicus under heat stress

Green Supplier Assessment and Selection for Sea Cucumber (Apostichopus japonicus) Processing Enterprise: Case Study in China

Green supply chain management is a crucial way to balance economic benefits and environmental impacts. As an important economic aquatic product in China, sea cucumber (Apostichopus japonicus) is facing the dual challenges of economic benefits (profit) and environmental sustainability (material input and emission output). Currently, the sea cucumber industry in China lacks a green supplier screening system, resulting in a fragmented pattern of cooperation among enterprises. Core enterprises in the supply chain cannot assume social responsibility to help and guide upstream and downstream enterprises to jointly improve environmental performance. This study focuses on the selection and evaluation of green suppliers for sea cucumber processing enterprises. Firstly, a green supplier assessment indicator system for sea cucumber processing enterprises was established, and the indicator weights were determined by the analytic hierarchy process (AHP) method. Next taking a large sea cucumber processing enterprise in Dalian, China, as an example, the importance level of each index was evaluated by fuzzy comprehensive evaluation (FCE), and the score and ranking of existing suppliers were determined. The validity and practicality of the method were verified. The results show that Supplier 1 (S1) has the highest score, and the price of sea cucumber farming, the cleaner production level of sea cucumber farming, environmental awareness, and long-term cooperation willingness were the most important factors in the selection of green suppliers for sea cucumber processing enterprises, which provides useful clues on the best practice of making sustainable development decisions. With an in-depth understanding of the key factors, suppliers can formulate different prices according to the differences in sales channels to improve the economic deficiencies. Environmental pollution can also be reduced by using clean energy, establishing a recirculating aquaculture system, and using micro-ecological preparations. The conclusions of this study can provide technical support and decision-making suggestions for the application of green supply chain management in China’s aquaculture industry.

Effects of alarm cues on behavior and physiology of the sea cucumber Apostichopus japonicus

Alarm cues have an inevitable impact on organisms in aquaculture. The present study investigated the effects of alarm cues on the sea cucumber Apostichopus japonicus from behavioral and physiological perspectives. We found that the adhesion time significantly increased in sea cucumbers exposed to alarm cues (P = 0.008), indicating that sea cucumbers do not easily fall off the attachment substance into a harsh environment in seed production. Novelly, this present study clarified that fleeing response of sea cucumbers exposed to alarm cues was driven by tail movement rather than head movement. There was no significant difference in tentacle activity frequency (P = 0.705), indicating that alarm cues would not affect feeding behavior of sea cucumbers. In addition, there was also no significant difference in righting behavior of A. japonicus (P = 0.724), indicating that sea cucumbers probably respond to alarm cues through tube feet rather than tentacles or muscles. We reveal that alarm cues do not affect all but some the behaviors of sea cucumbers. Further, the present study found no significant difference in cortisol concentration (P = 0.583). In contrast, 5-hydroxytryptamine (5-HT) concentration significantly increased in sea cucumbers exposed to alarm cues (P = 0.004). These results suggest that the effect of alarm cues is probably mediated by 5-HT in sea cucumbers. Further, the present study found that the movement speed had a significant decrease in sea cucumbers fed with 3% dietary tryptophan when being exposed to alarm cues (P < 0.001). Thus, we suggest aqua-farmers feed 3% tryptophan to optimize behaviors of A. japonicus in seed production. In addition, the present study found that the artificial reef significantly shortened the righting response time of sea cucumbers (P = 0.002), indicating that artificial reefs are beneficial to righting behavior of sea cucumbers exposed to alarm cues. This present study provides new insights into behavioral and physiological reactions to alarm cues and into seed production of sea cucumbers.

Unveiling the early life core microbiome of the sea cucumber Apostichopus japonicus and the unexpected abundance of the growth-promoting Sulfitobacter

BackgroundMicrobiome in early life has long-term effects on the host’s immunological and physiological development and its disturbance is known to trigger various diseases in host Deuterostome animals. The sea cucumber Apostichopus japonicus is one of the most valuable marine Deuterostome invertebrates in Asia and a model animal in regeneration studies. To understand factors that impact on host development and holobiont maintenance, host-microbiome association has been actively studied in the last decade. However, we currently lack knowledge of early life core microbiome during its ontogenesis and how it benefits the host’s growth.ResultsWe analyzed the microbial community in 28 sea cucumber samples from a laboratory breeding system, designed to replicate aquaculture environments, across six developmental stages (fertilized eggs to the juvenile stage) over a three years-period to examine the microbiomes’ dynamics and stability. Microbiome shifts occurred during sea cucumber larval ontogenesis in every case. Application of the most sophisticated core microbiome extraction methodology, a hybrid approach with abundance-occupancy core microbiome analyses (top 75% of total reads and > 70% occupation) and core index calculation, first revealed early life core microbiome consisted of Alteromonadaceae and Rhodobacteraceae, as well as a stage core microbiome consisting of pioneer core microbe Pseudoalteromonadaceae in A. japonicus, suggesting a stepwise establishment of microbiome related to ontogenesis and feeding behavior in A. japonicus. More interestingly, four ASVs affiliated to Alteromonadaceae and Rhodobacteraceae were extracted as early life core microbiome. One of the ASV (ASV0007) was affiliated to the Sulfitobactor strain BL28 (Rhodobacteraceae), isolated from blastula larvae in the 2019 raring batch. Unexpectedly, a bioassay revealed the BL28 strain retains a host growth-promoting ability. Further meta-pangenomics approach revealed the BL28 genome reads were abundant in the metagenomic sequence pool, in particular, in that of post-gut development in early life stages of A. japonicus.ConclusionRepeated rearing efforts of A. japonicus using laboratory aquaculture replicating aquaculture environments and hybrid core microbiome extraction approach first revealed particular ASVs affiliated to Alteromonadaceae and Rhodobacteraceae as the A. japonicus early life core microbiome. Further bioassay revealed the growth promoting ability to the host sea cucumber in one of the core microbes, the Sulfitobactor strain BL28 identified as ASV0007. Genome reads of the BL28 were abundant in post-gut development of A. japonicus, which makes us consider effective probiotic uses of those core microbiome for sea cucumber resource production and conservation. The study also emphasizes the importance of the core microbiome in influencing early life stages in marine invertebrates. Understanding these dynamics could offer pathways to improve growth, immunity, and disease resistance in marine invertebrates.

Global Analysis of 2-Hydroxy Fatty Acids by Gas Chromatography-Tandem Mass Spectrometry Reveals Species-Specific Enrichment in Echinoderms.

Abnormal levels of 2-hydroxy fatty acids (2-OH FAs) are characterized in multiple diseases, and their quantification in foodstuffs is critical to identify the sources of supplementation for potential treatment. However, due to the structural complexity and limited available standards, the comprehensive profiling of 2-OH FAs remains an ongoing challenge. Herein, an innovative approach based on gas chromatography-tandem mass spectrometry (GC-MS/MS) was developed to determine the full profile of these FA metabolites. MS and MS/MS spectra of the trimethylsilyl (TMS) derivatives of 2-OH fatty acid methyl esters (FAMEs) were collected for peak annotation by their signature fragmentation patterns. The structures were further confirmed by validated structure-dependent retention time (RT) prediction models, taking advantage of the correlation between the RT, carbon chain length, and double bond number from commercial standards and pseudostandards identified in the whole-brain samples from mice. An in-house database containing 50 saturated and monounsaturated 2-OH FAs was established, which is expandible when additional molecular species with different chain lengths and backbone structures are identified in the future. A quantitation method was then developed by scheduled multiple reaction monitoring (MRM) and applied to investigate the profiling of 2-OH FAs in echinoderms. Our results revealed that the levels of total 2-OH FAs in sea cucumber Apostichopus japonicas (8.40 ± 0.28 mg/g dry weight) and starfish Asterias amurensis (7.51 ± 0.18 mg/g dry weight) are much higher than that in sea urchin Mesocentrotus nudus (531 ± 108 μg/g dry weight). Moreover, 2-OH C24:1 is the predominant molecular species accounting for 67.9% of the total 2-OH FA in sea cucumber, while 2-OH C16:0 is the major molecular species in starfish. In conclusion, the current innovative GC-MS approach has successfully characterized distinct molecular species of 2-OH FAs that are highly present in sea cucumbers and starfish. Thus, these findings suggest the possibility of developing future feeding strategies for preventing and treating diseases associated with 2-OH FA deficiency.

Chemical substances and their activities in sea cucumber Apostichopus japonicus: A review.

Apostichopus japonicus, also known as Stichopus japonicus, with medicinal and food homologous figures, is a globally recognized precious ingredient with extremely high nutritional value. There is no relevant review available through literature search, so this article selects the research articles through the keywords "sea cucumber" and "Apostichopus japonicus (Stichopus japonicus)" in six professional databases, such as Wiley, PubMed, ScienceDirect, ACS, Springer, and Web of Science, from 2000 to the present, summarizing the extraction, isolation, and purification methods for the four major categories (polysaccharides, proteins and peptides, saponins, and other components) of the A. japonicus chemical substances and 10 effective biological activities of A. japonicus. Included are anticoagulation, anticancer/antitumor activities, hematopoiesis, regulation of gut microbiota, and immune regulatory activities that correspond to traditional efficacy. Literature support is provided for the development of medicines and functional foods and related aspects that play a leading role in future directions.

Sediment microbial community characteristics in sea cucumber restocking area

Variations of microbial species and functional composition in coastal sediment are usually taken as the results of the provision of supplementary nutrients affected by human activities. However, responses of microbiome stability to restocking biological resources remain less understood in coastal benthic systems without nutrient supplements. Here, combined with metagenomics and microbiome co-occurrence networks, the composition, function, and community stability of microbes were evaluated in a coastal area where sea cucumbers (Apostichopus japonicus) restocked after six months. Also, the physicochemical characteristics of sediments and bottom water were analyzed. We found the total organic carbon, total nitrogen, and total phosphorus of sediment did not change significantly in the restocking area after six months, whereas the concentration of dissolved inorganic nitrogen in bottom water increased significantly. Moreover, the relative abundance of Nitrospina at the class level was increased significantly in the restocking area. Also, enzymes related to nitrate reduction and nitrous oxide reductase were increased in the restocking area. Of note, stock enhancement of sea cucumbers altered associations between bacteria rather than their composition. The elimination of negative associations and reduction of the potential keystone taxa in the restocking area indicated destabilized bacterial communities. Our work may contribute to elucidating the response of microbial stability to stock enhancement. This finding also suggests that microbial community stability can be considered as an indicator of ecological risk under the influence of stock enhancement.

Analyses of regulation between miRNA and DNA methyltransferase 1 related genes in sea cucumber Apostichopusjaponicus

Analyses of regulation between miRNA and DNA methyltransferase 1 related genes in sea cucumber Apostichopusjaponicus

Transcriptomic analysis reveals the immune response mechanisms of sea cucumber Apostichopus japonicus under noise stress from offshore wind turbine

As an important form of renewable energy, offshore wind power can effectively reduce dependence on traditional energy sources and decrease carbon emissions. However, operation of wind turbines can generate underwater noise that may have negative impacts on marine benthic organisms in the surrounding area. Sea cucumbers are slow-moving invertebrates that inhabit the ocean, relying on their immune system to adapt to their environment. To evaluate the frequency range of characteristic noise produced by offshore wind turbines, we conducted a field survey. Additionally, we utilized sea cucumbers in simulated experiments to assess their response to the noise produced by offshore wind turbines. We established a control group, a low-frequency noise group simulating offshore wind turbine noise at 125 Hz and 250 Hz, and a high-frequency noise group at 2500 Hz, each lasting for 7 days. Results from measuring immune enzyme activity in the coelomic fluid suggest that noise can reduce the activity of superoxide dismutase enzymes, which may make sea cucumbers more susceptible to oxidative damage caused by free radicals. Exposure to low-frequency noise can have the effect of diminishing the activity of catalase, and this decrease in catalase activity could potentially increase the susceptibility of the sea cucumber's coelom to inflammation. In order to elucidate the hypothetical mechanism of immune response, intestinal tissue was extracted for transcriptome sequencing. The results showed that under 125 Hz low-frequency noise stress, the number of differentially expressed genes was the highest, reaching 1764. Under noise stress, sea cucumber's cell apoptosis and cell motility are reduced, interfering with lipid metabolism process and membrane synthesis. This research provides theoretical support for the environmental safety assessment of offshore wind power construction.

Metabolomic insights into neurological effects of BDE-47 exposure in the sea cucumber Apostichopus japonicus

The persistent organic pollutant 2,2′,4,4′-Tetrabromodiphenyl ether (BDE-47), a prevalent congener among polybrominated diphenyl ethers (PBDEs), exhibits potent bioaccumulation and toxicity. Despite extensive research into the adverse effects of BDE-47, its neurotoxicity in sea cucumbers remains unexplored. Given the crucial role of the sea cucumber's nervous system in survival and adaptation, evaluating the impacts of BDE-47 is vital for sustainable aquaculture and consumption. In this study, we employed ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Triple-TOF-MS) to analyze metabolomic changes in neuro-related tissues of Apostichopus japonicus exposed to low (0.1 µg/L), medium (1.0 µg/L), and high (10.0 µg/L) BDE-47 concentrations. We identified significantly changed metabolites in each exposure group (87 in low, 79 in medium, and 102 in high), affecting a variety of physiological processes such as steroid hormone balance, nucleotide metabolism, energy metabolism, neurotransmitter levels, and neuroprotection. In addition, we identified concentration-dependent, common, and some other metabolic responses in the neuro-related tissues. Our findings reveal critical insights into the neurotoxic effects of BDE-47 in sea cucumbers and contribute to risk assessment related to BDE-47 exposure in the sea cucumber industry, paving the way for future neurotoxicological research in invertebrates.

Evaluation of regulatory capacity of three lactic acid bacteria on the growth performance, non-specific immunity, and intestinal microbiota of the sea cucumber Apostichopus japonicus

Lactic acid bacteria (LAB) have been extensively used as probiotics in aquaculture. However, probiotic effects of different inter-generic strains of LAB on sea cucumber Apostichopus japonicus are still poorly understood. Here, sea cucumber were fed with five diets for 63 days, including a basal diet (the control, C group), a florfenicol diet (15 mg/kg; the positive control, FL group) and three LAB diets, i.e., the basal diets supplemented with Lactobacillus plantarum W2 (LP group), Enterococcus faecium LYB (EF group) and Pediococcus acidilactici Nj (PA group) at the dose of 1 × 1010 CFU/kg diet, respectively. A stimulation test with inactivated Vibrio splendidus was then performed and characterized immune responses of sea cucumber over 168 h. The results showed that all three LAB significantly enhanced the growth performance of sea cucumber, with the LP diet showed the best growth-promoting effect. The LP and PA diets significantly increased coelomocyte phagocytic, respiratory burst, superoxide dismutase, alkaline phosphatase, acid phosphatase, catalase, and lysozyme activities. The LP and EF diets significantly up-regulated the intestinal immune genes (Aj-p105, Aj-p50, Aj-rel, and Aj-lys) expression levels, while PA diet did not significantly up-regulate the Aj-p50 gene expression level. Meanwhile, all three LAB significantly enhanced intestinal immune response. Florfenicol diet significantly decreased phagocytic and alkaline phosphatase activities, down-regulated the Aj-lys gene expression, and suppressed intestinal immune response. L. plantarum W2 significantly increased the diversity of the intestinal microbiota in sea cucumber, and the P. acidilactici Nj significantly improved both the diversity and richness. A higher relative abundance of Actinobacteriota, norank_f_Rhodobacteraceae, and Sedimentitalea was observed in the LP, EF, and PA groups, respectively, while a lower relative abundance of Firmicutes was showed in the FL group. All three LAB improved the stability of the intestinal microbial networks and up-regulated the functional pathways of intestinal microbiota associated with amino acid metabolism. However, florfenicol reduced microbial network stability and significantly inhibited the intestinal microbiota functions. In conclusion, L. plantarum W2, E. faecium LYB, and P. acidilactici Nj can be effectively used as probiotics in sea cucumber aquaculture. Among them, L. plantarum W2 exhibited the best effect on sea cucumber when the growth performance, non-specific immunity, and intestinal microbial structure and functions were considered collectively.

A potential feeding regulation strategy during aestivation: Relaxation of intestine mediated by pedal peptide/orcokinin-type neuropeptides in sea cucumber Apostichopus japonicus

Aestivation is an important survival strategy that is used by a wide variety of organisms to cope with high environmental temperatures and/or arid conditions. Summer aestivation also occurs among marine animals living in shallow inshore waters. Sea cucumbers, Apostichopus japonicus, are an economically important species that are farmed extensively in shallow in-shore waters across Asia. In recent years, this species has also been developed as an important model for studying temperature-induced aestivation in the marine environment. Over about 100 days of summer aestivation A. japonicus stops feeding, experiences severe degeneration of the intestine and substantial body mass reduction, which seriously impacts production efficiency of sea cucumbers in aquaculture. Our previous studies of A. japonicus applied LC-MS/MS to reveal changes in neuropeptide expression during aestivation and identified pedal peptide/orcokinin (PP/OK)-type neuropeptides, an evolutionarily ancient regulator of muscle relaxation/contraction, as significantly up-regulated in the circumoral nerve ring (CNR) during A. japonicus aestivation. Based on this, we proposed that PP/OK-type neuropeptides are potentially key to regulate feeding and intestinal integrity during aestivation by regulating the mechanical behavior of intestine. The present study investigated PP/OK-type neuropeptides in A. japonicus tissues via histological, functional and ecological analyses. A widespread expression pattern, especially in the CNR, radial nerve cord (RNC) and intestine was revealed using real-time quantitative PCR and immunohistochemistry. Our findings show a key role for the expression of the neuropeptide, A. japonicus pedal peptide-type precursor 2 (AjPPLNP2), during the early stage of aestivation that increased significantly in the CNR and intestine as compared with the non-aestivating condition. Furthermore, in vitro pharmacological tests showed that three PP/OK-type neuropeptides confirmed by MS displayed relaxing effects on intestine, suggesting that PP/OK-type neuropeptides have a key involvement in A. japonicus aestivation by regulating relaxation of the intestine that halts normal peristalsis and inhibits feeding. In conclusion, our results suggest a mechanism for feeding inhibition controlled by neuropeptides and provide a potential regulatory strategy for counteracting intestine atrophy and body mass reduction in sea cucumber aquaculture by controlling the action of neuropeptides.

Bacillus licheniformis reduces mortality, improves symptoms, and controls residual pathogenicity in juvenile sea cucumbers Apostichopus japonicus infected with skin ulceration syndrome

Mass mortality caused by skin ulceration syndrome (SUS) is the bottle-neck for the sustainable aquaculture of the sea cucumber Apostichopus japonicus. In the present study, probiotic Bacillus licheniformis (0.25 × 109 CFU/g) was used as the treatment for A. japonicus infected with the SUS that caused by Vibrio harveyi. We found that B. licheniformis significantly reduced the number of infected sea cucumbers 5 days and 7 days after the treatment (group B), compared to those without B. licheniformis treatment (group C) (P < 0.001; P < 0.001). Further, the sea cucumbers fed B. licheniformis had significantly lower mortality at the end of the experiment (<10%) than that of those without the B. licheniformis treatment (>60%) (P < 0.001). These results suggest that the treatment of B. licheniformis is an effective method to reduce the mass mortality resulted from SUS in sea cucumber aquaculture. Further, 3–5 days of treatment significantly improved the adverse symptoms of SUS on the physiology and behavior of sea cucumbers, including the righting behavior, adhesion behavior, food consumption, fecal output and mobility. This indicates B. licheniformis treatment has the advantage in the recovery of sea cucumbers after SUS. Moreover, there was no significant difference observed in the physiology and behavior of sea cucumbers between the SUS infected sea cucumbers after the 7-day treatment of B. licheniformis and the healthy individuals. SUS infected sea cucumbers effectively returned to a stage of normalcy. Further, we found a significantly lower infected rate in sea cucumbers exposed to the culture water of group B (∼5%) than that of those in exposure to the culture water of group C (∼60%). This indicates that the treatment of B. licheniformis efficiently controls the residual pathogenicity of SUS in culture water. The present study demonstrated the effectiveness of B. licheniformis treatment as an environmentally friendly approach to reducing mortality, improving symptoms, and controlling residual pathogenicity in sea cucumber aquaculture.

Metagenomic insights into the energy metabolism and immune variation of sea cucumber Apostichopus japonicus during reproduction

Sea cucumber Apostichopus japonicus is important aquatic economic species in Asia. In recent years, due to the decline of wild resources of A. japonicus, in order to ensure the sustainable supply of seedlings, the broodstock rearing is particularly important during seedling production, reproduction is also an essential stage in the life history of A. japonicus. However，the physiology of marine animals undergoes variations during the process of reproduction. It is well known that the energy demand of broodstock increases and their immunity decreases during the reproduction. Intestinal microorganisms participate in host life activities, while the presence of pathogens and probiotics will affect host health. However, the function of intestinal microbiota in the energy and immunity during the reproduction remains unclear. In this study, we performed a metagenomic analysis of the gut microbiota in A. japonicus to investigate variations in microbial composition and KEGG pathways associated with reproductive periods. Results suggested that Firmicutes/Bacteroidetes (F/B) was gradually increasing during reproduction, which increased host energy harvest, and was difference between male and female A. japonicus. Virulence Factors of Pathogenic Bacteria (VFBD) upregulated from the gonadal growth period. The higher expression of VFBD during the gonadal growth period than at other times may be caused by the fact that Flavobacteriaceae and Rhodobacteraceae are most abundant during this period. Lysozyme activity was upregulated during reproduction and peaked during the gonadal mature period, with a similar trend of variability as in VFBD, which carried out immunological protection against A. japonicus. The relative abundance of Saccharomycetaceae, and Bacillaceae was highest during the spawning period, and it has been identified that microorganisms strengthen immune protection against A. japonicus during this period, when A. japonicus was in a weakened state. Based on KEGG analysis, expression of oxidative phosphorylation and the fever pathway increased after spawning, indicating that reproduction causes oxidative stress in A. japonicus. Additionally, the differences in several KEGG pathways were related to sex. Overall, by analyzing the energy and immune systems, the study confirmed that intestinal microorganisms play vital physiological roles in broodstock of A. japonicus during reproduction. This study provided important information for breeding and the application of A. japonicus in aquaculture.

Comparative transcriptome analysis reveals key genes and pathways related to gonad development in the sea cucumber Apostichopus japonicus

The sea cucumber Apostichopus japonicus is an economically important marine species in China, and understanding the mechanisms underlying its gonad development is crucial for successful reproduction and breeding. In this study, we performed transcriptome comparisons and analyses of A. japonicus gonadal and non-gonadal tissues to identify genes and molecular pathways associated with gonadal development. We also supplemented the annotation of the A. japonicus genome. Collectively, results revealed a total of 941 ovary-specific genes and 2499 testis-specific genes through different expression analysis and WGCNA analysis. The most enriched pathways in ovary and testis were “DNA replication” and “purine metabolism”, respectively. Additionally, we identified key candidate gene modules that control gonad development and germ cell maturation, with CDT1 and DYNC2LI1 serving as hub genes. Our findings provide important insights into the gonadal development system of A. japonicus and offer valuable references for further research on reproductive biology in this marine invertebrate species.

Effects of Scallop Visceral Mass and Mantle as Dietary Supplements on the Growth, Immune Response and Intestinal Microflora of Juvenile Sea Cucumber Apostichopus japonicus.

Scallop visceral mass and mantle are aquatic byproducts and waste, but they have high contents of protein. In this study, scallop visceral mass and mantle were used as supplements in the diet of juvenile sea cucumber (A. japonicus) and their effects on the growth, fatty acid and amino acid compositions, the non-specific immune responses and the intestinal microflora of A. japonicus were investigated through a 40 d feeding experiment. The results showed that dietary supplementation of scallop visceral mass significantly accelerated the specific growth rate (SGR) of juvenile A. japonicus by 3 times within 20 days, and also raised the contents of ω-3 fatty acids including EPA and DHA and the ω-3/ω-6 ratio of the sea cucumber tissue, which is favorable to the health and commercial value of the sea cucumber. Furthermore, it was found that the supplementation of scallop visceral mass and mantle stimulated the expression of immune-related genes and enhanced the immune defense in A. japonicus. Scallop visceral mass and mantle supplementation also increased the microbial diversity and the abundance of beneficial microbes including Bifidobacteriaceae, Streptomycetaceae, Clostridiaceae and Rhizobiales in the gut of A. japonicus. This study reveals the beneficial effects of dietary supplementation of scallop visceral mass and mantle on the growth of juvenile A. japonicus, which might be a promising way to reutilize this scallop waste and raise its economic value.

Ajpacifastin-like is involved in the immune response of Apostichopus japonicus challenged by Vibrio splendidus.

Pacifastin proteins are previously found to regulate the phenoloxidase system in invertebrates and arthropods. In this study, the immune response that was regulated by Ajpacifastin-like in the sea cucumber Apostichopus japonicus was determined. RNA interference was used to knock down the expression of the Ajpacifastin-like gene in A. japonicus, followed by challenge with Vibrio splendidus, and the colony count showed that the survival of V. splendidus in the si-Ajpacifastin group increased 4.64-fold compared to that of the control group. The purified recombinant Ajpacifastin-like showed an inhibitory effect on the extracellular protease activity of the supernatant collected from the V. splendidus culture. Consequently, a comparative transcriptome analysis of the coelomocytes from the control group and the si-Ajpacifastin group was performed to explore the global regulatory effect of the Ajpacifastin-like. A total of 1486 differentially expressed genes (DEGs) were identified, including 745 upregulated genes and 741 downregulated genes. GO enrichment showed that the DEGs were mainly enriched in translation, cytosolic ribosomal subunit and structural constituent of ribosome. KEGG analysis showed that the DEGs were significantly enriched in the retinoic acid-inducible gene I (RIG-I)-like receptor signaling pathway, antigen processing and presentation, toll-like receptor signaling pathway, mitogen-activated protein kinase signaling pathway, nuclear factor-kappa B signaling pathway and other immune-related pathways. Furthermore, real-time reverse transcriptase PCR was used to determine the RNA levels of six DEGs, i.e., cathepsinB, CYLD, caspase8, TRAF6, hsp90 and FADD, to verify the RNA-seq results. Overall, our results specified the immune response and pathways of A. japonicus in which Ajpacifastin-like was involved in.

Inferring potential causative microbial factors of intestinal atrophic disease in the sea cucumber Apostichopus japonicus

The overexploitation of the wild populations of Apostichopus japonicus has caused a significant decline in their numbers, prompting the establishment of a sea cucumber aquaculture industry that has become a major player in East Asia. Recent research has focused on identifying the various factors that may affect sea cucumber aquaculture, including water quality, diet, and the microbiome associated with their hosts. Notably, studies on host-associated microbiomes have emerged as a prominent area of research, particularly in the context of investigating the relationship of the microbiome with diseases that have caused significant economic losses. Intestinal atrophy of A. japonicus larvae has been reported at a number of sea cucumber farms in Japan, but there have been no factor screenings, and there is currently no efficient mitigation. In this study, we applied metagenomic analyses for the first time to an intestinal atrophic case of the sea cucumber A. japonicus larvae, which occurred in an aquaculture facility in Hokkaido, Japan, elucidating potential causative microbial factors and comparing the diseased microbiome against the healthy pan-microbiome. Through our metagenome comparisons, we have found significant increases in Oceanicoccus, Ruegeria, Nioella, Labrenzia, Tenacibaculum, and Muricauda in the diseased larvae. Among those, Tenacibaculum was estimated to potentially be the most pathogenic bacterium in the development of intestinal atrophic disease due to previous outbreaks of sea urchin diseases in the same facility. Our metagenomic approach demonstrates the further need of microbial screening of such causative agents and identification of the pathogenesis of such diseases, which could contribute to establishing more sustainable aquaculture in the sea cucumber industry.