Effect of low-frequency noise on the survival rate and immunity of infected Vibrio parahaemolyticus sea slug (Onchidium reevesii)

Unravelling the pathogenesis of Vibrio parahaemolyticus infection: impacts on antioxidant and innate immunity gene responses in Scyllaparamamosain

This study investigated the etiology of Vibrio parahaemolyticus in mud crabs (Scylla paramamosain), a pivotal species in China's aquaculture industry. The results demonstrate that the V. parahaemolyticus strain LG2206 poses a significant threat to mud crabs by inducing oxidative stress and impairing their non-specific immune response. A 7-day immersion contagion test was conducted to determine the lethal dose 50 (LD50) of LG2206 for the mud crabs, which was established at 3.16 × 105 CFU/mL. The findings indicate that LG2206 can infiltrate multiple tissues of the mud crab, with the gills being the initial and primary site of invasion, followed by the hepatopancreas, midgut, and muscle. Throughout the infection period, an increasing LG2206 count across sampled tissues led to tissue damage and cell death, with the gills, hepatopancreas, midgut, and muscle affected in sequence. The modulation of various enzymatic and genetic responses to LG2206 incubation was also investigated. Notably, superoxide dismutase (SOD) and glucocorticoid reductase (GR) were upregulated in the gill tissue. Phenoloxidase (PO) and lysozyme (LZM) exhibited a transient surge on the first day post-infection, followed by a decline. Enzymatic activity in other tissues followed a pattern of initially increasing, peaking, and then gradually declining, with the gills, hepatopancreas, midgut, and muscle following this trend sequentially. Additionally, the expression patterns of heat shock protein 70 (HSP70) and CASP-3 genes mirrored this trend, with their peaks occurring at different times across the various tissue types. In summary, this study sheds light on the pathogenic process of LG2206 in mud crabs, revealing that V. parahaemolyticus initially adheres to and compromises gill tissue before spreading through the circulatory system to other organs, with a preference for the hepatopancreas. This work enhances our understanding of the effects of V. parahaemolyticus on mud crab farming and proposes potential intervention strategies to mitigate its harmful impacts.

Systemic protection through enhanced immunity and antioxidant defenses in immune-primed Mytilus coruscus: Insights from cell/tissue-specific analyses

Marine mussels are constantly exposed to pathogens and have to evolve robust immune systems to recognize, tolerate and clear infections. Recent studies have highlighted the phenomenon of 'immune priming' and its role in enhanced immunity in invertebrate. Yet, there is still a lack of experimental evidence on mussels of economic value. This study investigated the potential protective effects of immune priming in hemocytes and key tissues of marine mussels (Mytilus coruscus) which were repeatedly challenged with Vibrio alginolyticus, focusing on systemic responses in survival, immune functions and antioxidant responses. The results indicated that, hemocytes, as the immune cells in mussels, initiated the immune function against Vibrio through pathogen recognition. Subsequently, toxin efflux and immune defenses were precisely regulated by promoting the inflammatory response and cell apoptosis to eliminate Vibrio and infected host cells. In parallel, antioxidant defense was coordinated to mitigate the potential oxidative stress generated during immune process. Further analysis revealed tissue-specific immune responses, with gill and digestive gland showing differential responses compared to hemocytes. Immune tolerance in gills was observed, while digestive glands exhibited sustained immune and antioxidant responses, supporting the idea that these tissues play distinct roles in maintaining homeostasis and combating pathogens. As the result, mussels in the immune-primed group exhibited slower mortality and maintained higher hemocyte viability compared to the non-primed ones, suggesting that immune priming in mussels can provide systemic protection by enhancing both cellular immunity and antioxidant defense. The results offer valuable insights into improving disease resistance in mussels' aquaculture systems.

Simultaneous exposure to microplastics and heavy metal lead induces oxidative stress, histopathological damage, and immune dysfunction in marine mussel Mytilus coruscus

The increasing deposition of microplastics (MPs) in aquatic ecosystems is a worldwide concern. MPs can interact with other environmental pollutants, such as heavy metals, and change their toxicity. In this study, we focused on the effects of MPs and lead (Pb), as a toxic heavy metal, on marine mussel Mytilus coruscus under separate and co-exposure situations at environmentally relevant concentrations: MPs (1 mg/L) and Pb (50 μg/L). We found that MPs alone or in combination with Pb significantly decreased the respiration and filtration rates of the mussels (p < 0.05). Histological observations revealed varying extents of damage to the gill and digestive gland caused by a single exposure to MPs, which was aggravated by co-exposure to Pb. In addition, co-exposure induced a higher level of oxidative stress, which was reflected by an increase in hydrogen peroxide and malondialdehyde content, and a decrease in antioxidant enzyme activity. Meanwhile, co-exposure poses a significant threat to the immune function of the mussels, as evidenced by induction of hemocytes to produce excess reactive oxygen species (ROS), significantly reducing lysosome activity (p < 0.05), inhibiting the expression of autophagy-related genes, and inducing the expression of apoptosis-related genes, resulting in hemocyte apoptosis. Furthermore, the TLR/MyD88/NFκB signaling pathway is involved in the immune response of mussels to environmental stress. This study provides novel perspectives on the toxicity of MPs combined with Pb in marine animals, as well as the molecular mechanisms underlying their ecotoxicological effects.

Molecular insights into the physiological impact of low-frequency noise on sea slug Onchidium reevesii: Activation of p53 signaling and oxidative stress response

To investigate the regulatory role of tumor protein p53 of sea slug (Onchidium reevesii) under oxidative stress conditions, we examined the response mechanisms of O. reevesii to low-frequency noise pollution (1000 Hz) using molecular and cellular biology techniques. We successfully cloned the O. reevesii p53 gene (Orp53) from O. reevesii, obtaining a 3356 bp sequence containing a 2727 bp open reading frame (ORF). Phylogenetic analysis revealed that O. reevesii shares a close evolutionary relationship with other molluscs, including Bulinus truncatus and Elysia marginata. Expression analysis showed that Orp53 is expressed across various tissues, with the highest expression levels in the hepatopancreas. Using RNA interference (RNAi) to silence the Orp53 gene, we found that the mRNA expressions of Orp53 and its downstream apoptosis-related genes, including cytochrome C (Cyt_C), Caspase 9, and Caspase 3, were significantly suppressed until the third day of interference (P < 0.05). Moreover, sip53 treatment resulted in significant reductions in the mRNA expression and protein levels of all studied genes (P < 0.05) compared to the noise-exposed group. In addition, the low-frequency noise exposure decreased central nervous system (CNS) viability while increasing oxidative stress markers, including reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and glutathione S-transferase (GST). On the other hand, silencing Orp53 expression via siRNA resulted in significant reductions in CNS cell viability (P < 0.05). Our study establishes a molecular basis for evaluating the consequences of marine noise pollution, confirming that low-frequency noise activates the p53 signaling pathway, oxidative stress, and that p53 can regulate oxidative stress and apoptosis-related genes.

Repeated marine heatwaves aggravate the adverse effects of nano-TiO2 on physiological metabolism of the thick-shelled mussel Mytilus coruscus

Global climate change is a major trigger of unexpected temperature fluctuations. The impacts of marine heatwaves (MHWs) and nano-titanium dioxide (nano-TiO2) on marine organisms have been extensively investigated. However, the potential mechanisms underlying their interactive effects on physiological processes and metabolism remain poorly understood, especially regarding periodic MHWs in real-world conditions. In this study, the effects of nano-TiO2 (at concentrations of 0, 25, and 250 μg/L) and periodic MHWs on the condition index (CI) and underlying metabolic mechanisms were investigated in mussels (Mytilus coruscus). The results showed that mussels try to upregulate their respiration rate (RR) to enhance aerobic metabolism (indicated by elevated succinate dehydrogenase) under short-term nano-TiO2 exposure. However, even at ambient concentration (25 μg/L), prolonged nano-TiO2 exposure inhibited ingestion ability (decreased clearance rate) and glycolysis (inhibited pyruvate kinase, hexokinase, and phosphofructokinase activities), which led to an insufficient energy supply (decreased triglyceride, albumin, and ATP contents). Repeated thermal scenarios caused more severe physiological damage, demonstrating that mussels are fragile to periodic MHWs. MHWs decreased the zeta potential of the nano-TiO2 particles but increased the hydrodynamic diameter. Additionally, exposure to nano-TiO2 and periodic MHWs further affected aerobic respiration (inhibited lactate dehydrogenase and succinate dehydrogenase activities), metabolism (decreased RR, activities of respiratory metabolism-related enzymes, and expressions of PEPCK, PPARγ, and ACO), and overall health condition (decreased ATP and CI). These findings indicate that the combined stress of these two stressors exerts more detrimental impact on the physiological performance and energy metabolism of mussels, and periodic MHWs exacerbate the toxicological effects of ambient concentration nano-TiO2. Given the potential worsening of nanoparticle pollution and the increase in extreme heat events in the future, the well-being of mussels in the marine environment may face further threats.

Low-frequency noise impairs righting reflex behavior by disrupting central nervous system in the sea slug Onchidium reevesii

Anthropogenic noise has significantly increased due to human activities, posing a threat to the health and survival of marine organisms. However, current studies have often emphasized its effects on the physiological aspects of marine organisms, while ignored the relationship between the neuroendocrine system and behavior. This study aimed to evaluate the righting behavior and relevant physiological functions of the central nervous system (CNS) in sea slug (Onchidium reevesii) exposed to low-frequency noise and subsequent noise removal. The duration of the sea slugs' righting reflex increased with longer noise exposure time. The degree of neuronal cell damage and apoptosis were significantly increased and relevant gene expressions were affected (Glu, AChE, FMRFamide and CaMKII) (P < 0.05). After the removal of noise, the righting reflex speed gradually recovered, and the degree of neuronal cell damage, apoptosis and the expression levels of genes continued to decrease. Pearson correlation analysis showed that the righting time was positively correlated with CNS tissue and DNA damage, apoptosis rate, and negatively correlated with the expression levels of genes. Therefore, low-frequency noise exposure causes damage to the CNS of sea slugs, subsequently impairing their normal behavior. Sea slugs exhibited partial recovery within 384 h after removing noise. These findings provide valuable insights into the effects of low-frequency noise on the CNS and behavior of marine invertebrates.

Cloning and characterization of heat shock transcription factor 1 and its functional role for Hsp70 production in the sea slug Onchidium reevesii

To investigate the regulatory role of heat shock transcription factor 1 of sea slug Onchidium reevesii (OrHSF1) on Hsp70 expression in the sea slug under stress , the OrHSF1 gene was cloned and bioinformatics analysis was performed, then the gene and protein expressions by RNA interference (RNAi) mediated knockdown of OrHSF1 expression were measured to clarify the regulatory relationship between OrHSF1 and Hsp70 under low-frequency noise (LFN) stress. Our study was the first to clone a 1572 bp sequence of the OrHSF1 gene, with the sequence coding for amino acids (CDS) being 729 bp, encoding 243 amino acids. O. reevesii shared a close evolutionary relationship with mollusks such as the Aplysia californica. OrHSF1 gene is widely expressed in different tissues of sea slugs, with the highest expression in the intestine and the lowest in the reproductive glands. Furthermore, we used RNA interference (RNAi) as a tool to silence the OrHSF1 gene in the central nervous system (CNS) and the results indicated that gene silencing was occurring systematically in the CNS and the suppression of OrHSF1 expression by RNAi-mediated gene silencing altered the expression of Hsp70; besides, the expression trends of OrHSF1 gene and Hsp70 were consistent in the 3 and 5-day RNAi experiment. Moreover, in sea slugs injected with siHSF1 and exposed to LFN, the mRNA expression and protein expression of Hsp70 in the CNS were significantly decreased compared to the low-frequency noise group (P < 0.05). This study demonstrated that OrHSF1 regulates Hsp70 expression in marine mollusks under low-frequency noise, and HSF1-Hsp70 axis plays a key role in stress response.