Effects of a Sudden Drop in Salinity on Immune Response Mechanisms of Anadara kagoshimensis

Physiological and transcriptomic analysis provides new insights into osmoregulation mechanism of Ruditapes philippinarum under low and high salinity stress

The Manila clam (Ruditapes philippinarum) is a commercially important marine bivalve, which inhabits the estuarine and mudflat areas. The osmoregulation is of great significance for molluscs adaptation to salinity fluctuations. In this study, we investigated the effects of low salinity (10 psu) and high salinity (40 psu) stress on survival and osmoregulation of the R. philippinarum. The results of physiological parameters showed that the ion (Na+, K+, Cl-) concentrations and Na+/K+-ATPase (NKA) activity of R. philippinarum decreased significantly under low salinity stress, but increased significantly under high salinity stress, indicating that there are differences in physiological adaptation of osmoregulation of R. philippinarum. In addition, we conducted the transcriptome analysis in the gills of R. philippinarum exposed to low (10 psu) and high (40 psu) salinity challenge for 48 h using RNA-seq technology. A total of 153 and 640 differentially expressed genes (DEGs) were identified in the low salinity (LS) group and high salinity (HS) group, respectively. The immune (IAP, TLR6, C1QL4, Ank3), ion transport (Slc34a2, SLC39A14), energy metabolism (PCK1, LDLRA, ACOX1) and DNA damage repair-related genes (Gadd45g, HSP70B2, GATA4) as well as FoxO, protein processing in endoplasmic reticulum and endocytosis pathways were involved in osmoregulation under low salinity stress of R. philippinarum. Conversely, the ion transport (SLC6A7, SLC6A9, SLC6A14, TRPM2), amino acid metabolism (GS, TauD, ABAT, ALDH4A1) and immune-related genes (MAP2K6, BIRC7A, CTSK, GVIN1), and amino acid metabolism pathways (beta-Alanine, Alanine, aspartate and glutamate, Glutathione) were involved in the process of osmoregulation under high salinity stress. The results obtained here revealed the difference of osmoregulation mechanism of R. philippinarum under low and high salinity stress through physiological and molecular levels. This study contributes to the assessment of salinity adaptation of bivalves in the context of climate change and provides useful information for marine resource conservation and aquaculture.

Developmental toxicity and potential mechanisms exposed to polystyrene microplastics and polybrominated diphenyl ethers during early life stages of fat greenling (Hexagrammos otakii)

The occurrence of microplastics (MPs) in aquatic ecosystems and their ability to absorb hydrophobic pollutants, such as persistent organic pollutants (POPs), is currently a significant concern. MPs, which are the main breakdown product of plastics, have been frequently detected in the environment, posing serious threats to organisms' health. One particular pollutant, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), is a dominant congener of PBDEs and is highly toxic to organisms. However, there is limited knowledge regarding the exposure of marine fishes to PBDEs through MPs and their combined toxic effects. In this study, the embryo toxicity of Hexagrammos otakii was conducted to investigate the combined effects of MPs and BDE-47. The results showed that MPs and BDE-47 co-exposure had detrimental effects on embryonic development, such as reduced hatchability, increased mortality, decreased heart rate, and body malformation. Moreover, the combined toxicity of these substances appeared more pronounced harmful effects compared to exposure to BDE-47 alone. Histopathological examination revealed that co-exposure can cause greater damage to hatching glands and yolk. The enrichment of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways included phagosome, metabolism of xenobiotics by cytochrome P450, TCA cycle, and Wnt signaling pathway, which are closely related to embryonic growth. BDE-47 and MPs may activate the Wnt signaling pathway to affect the normal development of embryos. Our results suggest that MPs and BDE-47 exposure may cause growth disorders in the early life stages of H.otakii, leading to abnormal embryonic development. All these results will contribute to the further study of the ecological risk assessment and toxicity of MPs and organic pollutant mixtures in marine fish.

Temporal dynamics of stress response in Halomonas elongata to NaCl shock: physiological, metabolomic, and transcriptomic insights

BACKGROUND

The halophilic bacterium Halomonas elongata is an industrially important strain for ectoine production, with high value and intense research focus. While existing studies primarily delve into the adaptive mechanisms of this bacterium under fixed salt concentrations, there is a notable dearth of attention regarding its response to fluctuating saline environments. Consequently, the stress response of H. elongata to salt shock remains inadequately understood.

RESULTS

This study investigated the stress response mechanism of H. elongata when exposed to NaCl shock at short- and long-time scales. Results showed that NaCl shock induced two major stresses, namely osmotic stress and oxidative stress. In response to the former, within the cell's tolerable range (1-8% NaCl shock), H. elongata urgently balanced the surging osmotic pressure by uptaking sodium and potassium ions and augmenting intracellular amino acid pools, particularly glutamate and glutamine. However, ectoine content started to increase until 20 min post-shock, rapidly becoming the dominant osmoprotectant, and reaching the maximum productivity (1450 ± 99 mg/L/h). Transcriptomic data also confirmed the delayed response in ectoine biosynthesis, and we speculate that this might be attributed to an intracellular energy crisis caused by NaCl shock. In response to oxidative stress, transcription factor cysB was significantly upregulated, positively regulating the sulfur metabolism and cysteine biosynthesis. Furthermore, the upregulation of the crucial peroxidase gene (HELO_RS18165) and the simultaneous enhancement of peroxidase (POD) and catalase (CAT) activities collectively constitute the antioxidant defense in H. elongata following shock. When exceeding the tolerance threshold of H. elongata (1-13% NaCl shock), the sustained compromised energy status, resulting from the pronounced inhibition of the respiratory chain and ATP synthase, may be a crucial factor leading to the stagnation of both cell growth and ectoine biosynthesis.

CONCLUSIONS

This study conducted a comprehensive analysis of H. elongata's stress response to NaCl shock at multiple scales. It extends the understanding of stress response of halophilic bacteria to NaCl shock and provides promising theoretical insights to guide future improvements in optimizing industrial ectoine production.

Effects and Molecular Regulation Mechanisms of Salinity Stress on the Health and Disease Resistance of Grass Carp

Though some freshwater fish have been successfully cultivated in saline-alkali water, the survival rates of freshwater fish are greatly affected by different saline-alkali conditions. The mechanisms of immune adaptation or immunosuppression of freshwater fish under different saline-alkali stress remain unclear. Here, grass carp were exposed to 3‰ and 6‰ salinity for 30 days. It was observed that salinity treatments had no obvious effects on survival rates, but significantly increased the percent of unhealthy fish. Salinity treatments also increased the susceptibility of grass carp against Flavobacterium columnare infection. The fatality rate (16.67%) of grass carp treated with 6‰ salinity was much lower than that treated with 3‰ salinity (40%). In the absence of infection, higher numbers of immune-related DEGs and signaling pathways were enriched in 6‰ salinity-treated asymptomatic fish than in 3‰ salinity-treated asymptomatic fish. Furthermore different from salinity-treated symptomatic fish, more DEGs involved in the upstream sensors of NOD-like receptor signaling pathway, such as NLRs, were induced in the gills of 6‰ salinity-treated asymptomatic fish. However in the case of F. columnare infection, more immune-related signaling pathways were impaired by salinity treatments. Among them, only NOD-like receptor signaling pathway was significantly enriched at early (1 and/or 2 dpi) and late (7 dpi) time points of infection both for 3‰ salinity-treated and 6‰ salinity-treated fish. Besides the innate immune responses, the adaptive immune responses such as the production of Ig levels were impaired by salinity treatments in the grass carp infected with F. columnare. The present study also characterized two novel NLRs regulated by salinity stress could inhibit bacterial proliferation and improve the survival rate of infected cells. Collectively, the present study provides the insights into the possible mechanisms why the percent of unhealthy fish in the absence of infection and mortality of grass carp in the case of F. columnare infection were much lower in the 6‰ salinity-treated grass carp than in 3‰ salinity-treated grass carp, and also offers a number of potential markers for sensing both environmental salinity stress and pathogen.

Cellular osmoregulation of the ark clam (Anadara kagoshimensis) hemocytes to hyposmotic media

Many bivalve species are considered to be euryhaline organisms due to effective adaptation to fluctuations of environmental salinity. Cellular mechanisms responsible for tolerance to salinity changes remain unclear for bivalves despite this question being critically important for commercially cultured species frequently introduced into regions differing from natural habitat by salinity regime. In the present work laser diffraction method was used for the analysis of volume changes in hemoglobin-containing ark clam (Anadara kagoshimensis) hemocytes following hyposmotic stimulation. Hemocytes responded to hyposmotic shock (decrease of media osmolarity from 461 to 216 mОsm/L) by a rapid swelling up to 171.5 ± 15.2% of control level. At normal osmotic conditions (osmolarity 461 mOsm/L), hemocyte mean cellular volume (MCV) was 354.0 ± 24.4 fl and maximum MCV of hyposmotically swollen cells prior lysis was 555.5 ± 57.4 fl (at the osmolarity 194 mOsm/L). Ark clam hemocytes demonstrated volume recovery response following hyposmotic swelling. Regulatory volume decrease (RVD) reaction did not depend on hemoglobin confirmation status. Final MCV of swollen hemocytes at the end of experimental period of RVD in oxygenated and deoxygenated suspensions did not significantly differ.

Discrepancy of apoptotic events in mouse hepatocytes and catalase performance: Size-dependent cellular and molecular toxicity of ultrafine carbon black

The diversification of the production process and application of ultrafine carbon black (UFCB), one of the nanomaterials, make the difference in particle sizes that exposed to environment. Currently, few size-dependent toxicity studies of UFCB pay attention to targeted effects on detoxification organs. And there is a research gap in the size-dependent molecular toxicity of UFCB. Based on this, mouse hepatocytes and catalase (CAT) were used as targeted receptors for UFCB size-dependent cellular and molecular toxicity studies. Results indicate that UFCB_13 nm induced higher ROS and lipid peroxidation levels. And the cell viability decreased to 22.5%, which is sharp contrast to UFCB_50 nm (45.3%) and UFCB_95 nm (55.1%). Mitochondrial dysfunction and a 25.2% early apoptosis rate are the further manifestation of the stronger cytotoxicity of UFCB_13 nm. At the molecular level, the exposure of UFCB with better dispersity resulted in more significant changes in the CAT backbone and secondary structure, fluorescence sensitization and enzyme function inhibition. The combined experiments show that the cellular uptake and dispersity of UFCB are the dominating factors for the discrepancy in size-dependent cellular and molecular toxicity, respectively. This study provides a theoretical basis for the necessary circumvention and substitution of UFCB in engineering applications.

Nanoplastic-Induced Genotoxicity and Intestinal Damage in Freshwater Benthic Clams (Corbicula fluminea): Comparison with Microplastics

With the wide application of plastics in daily life, nanoplastics (NPs) are ubiquitous in freshwater environments. However, to date, few studies have focused on the mechanism underlying the toxicity of NPs, and the differences between this mechanism and that governing the toxicity of MPs have also not been thoroughly characterized. In this study, the genotoxicity, intestinal damage, and intestinal flora in Corbicula fluminea exposed to micro/nanoplastics were investigated through RNA sequencing, histopathology, and 16S rRNA sequencing, respectively. Significant differences in differentially expressed genes (DEGs) were observed between MP and NP exposure groups. It was observed that NPs preferentially elicited the process related to cellular components and triggered the apoptosis through the mitochondrial pathway in various tissues, especially in indirectly contacted tissues, while MPs induced the innate immune response and activated the complement and coagulation cascades (complement system) pathway. Both MPs and NPs can induce an inflammatory response and cause epithelial damage in the intestines, and they can notably change the gut microbial community structure. However, the abundance of pathogenic bacteria (e.g., Mycoplasma) was observed to increase only in the MP-treated group, which exacerbated intestinal damage. Unlike MPs, the effect of NPs on the intestinal microflora was highly limited, while NPs elicited more severe damage to the intestinal mucosal barrier. The results of this study may help to elucidate the toxicity mechanisms governing the responses of bivalves to MPs and NPs and to evaluate the detriment of MPs and NPs to the benthic ecosystem.

IMPACT OF LOW SALINITY ON HEMOCYTES MORPHOLOGY AND FUNCTIONAL ASPECTS IN INVASIVE CLAM ANADARA KAGOSHIMENSIS (TOKUNAGA, 1906)

Impact of low salinity on morphology and function of hemocytes in ark clam species Anadara kagoshimensis was investigated using light microscopy and flow cytometry. In control group the water salinity was adjusted to 19.6‰, and experimental group was maintained at 14.8‰ and 8.8‰. Two cell types, amebocytes and erythrocytes, were identified in control group of ark clams. Erythrocytes constituted the main type of the cells, and amounted to 92.3±3.9 %. Hyposalinity changed that proportion: the number of amebocytes decreased 2.7 times and number of erythrocytes increased 7.6 times. Morphometric characteristics of hemocytes didn’t show statistically significant changes. As far as salinity decreased, the number of erythrocyte shades in hemolymph increased (3.5 times at salinity 8.8‰) and, in hemocytes, the reactive oxygen species (ROS) production grew (3.5. times at salinity 8.8‰).

Novel insights into host-pathogen interactions of large yellow croakers ( Larimichthys crocea) and pathogenic bacterium Pseudomonas plecoglossicida using time-resolved dual RNA-seq of infected spleens

Host-pathogen interactions are highly complex, involving large dynamic changes in gene expression during infection. These interactions are fundamental to understanding anti-infection immunity of hosts, as well as the pathogenesis of pathogens. For bacterial pathogens interacting with animal hosts, time-resolved dual RNA-seq of infected tissue is difficult to perform due to low pathogen load in infected tissue. In this study, an acute infection model of Larimichthys crocea infected by Pseudomonas plecoglossicida was established. The spleens of infected fish exhibited typical symptoms, with a maximum bacterial load at two days post-injection (dpi). Time-resolved dual RNA-seq of infected spleens was successfully applied to study host-pathogen interactions between L. crocea and P. plecoglossicida. The spleens of infected L. crocea were subjected to dual RNA-seq, and transcriptome data were compared with those of noninfected spleens or in vitro cultured bacteria. Results showed that pathogen-host interactions were highly dynamically regulated, with corresponding fluctuations in host and pathogen transcriptomes during infection. The expression levels of many immunogenes involved in cytokine-cytokine receptor, Toll-like receptor signaling, and other immune-related pathways were significantly up-regulated during the infection period. Furthermore, metabolic processes and the use of oxygen in L. crocea were strongly affected by P. plecoglossicida infection. The WGCNA results showed that the metabolic process was strongly related to the entire immune process. For P. plecoglossicida, the expression levels of motility-related genes and flagellum assembly-related genes were significantly up-regulated. The results of this study may help to elucidate the interactions between L. crocea and P. plecoglossicida.

Effects of a Sudden Drop in Salinity on Scapharca subcrenata Antioxidant Defenses and Metabolism Determined Using LC-MS Non-targeted Metabolomics

In this experiment, the effects of a sudden drop in salinity on the antioxidant defense system and related gene expression of the ark shell Scapharca subcrenata were examined. The sudden drop in seawater salinity after a rainstorm was simulated, and subsequently differentially expressed metabolic markers were identified by LC-MS non-targeted metabolomics. When the salinity dropped to 14‰ (S14), the total anti-oxidant content, activity of Na⁺/K⁺-ATPase, superoxide dismutase (SOD), and catalase (CAT), content of malondialdehyde, and expression levels of Mn-SOD, CAT, and C-type lectin of S. subcrenata were significantly higher than in groups with salinity of 22‰ (S22) or 30‰ (S30) (P < 0.05). The activity of glutathione peroxidase (GPx), the content of reduced glutathione, and the expression levels of GP_x were not significantly different between S14 and S22, but the values in each group were significantly higher than those in S30 (P < 0.05). Using the metabolomics technique, 361, 271, and 264 metabolites with significant differences were identified from S22 vs. S14, S30 vs. S14, and S30 vs. S22, respectively. The drop in salinity was accompanied by up-regulation of phosphatidylcholine (PC) (20:4 (5Z, 8Z, 11Z, 14Z)/P-18: 1 (11Z)), PC (16:0/22: 6 (4Z, 7Z, 10Z, 13Z, 16Z, 19Z)), phosphatidylethanolamine (PE) (18:4 (6Z, 9Z, 12Z, 15Z)/24:1 (15Z)), phosphatidylinositol (PI) (20:1 (11Z)/0:0), phalluside-1, C16 sphinganine, and LacCer (d18:0/14:0) and by significant down-regulation of PI-Cer (d18:1/14:0) and PE (14:0/16:1(9Z). The results of this study illustrate how these nine metabolites can be used as metabolic markers for the response of S. subcrenata to a sudden drop in salinity. They also provide the theoretical groundwork for selection of bottom areas with salinity that is optimal for release and proliferation of S. subcrenata, which is needed to restore the declining populations of this species.

Identification and Characterization of microRNAs in the Developing Seed of Linseed Flax (Linum usitatissimum L.)

Seed development plays an important role during the life cycle of plants. Linseed flax is an oil crop and the seed is a key organ for fatty acids synthesis and storage. So it is important to understand the molecular mechanism of fatty acid biosynthesis during seed development. In this study, four small RNA libraries from early seeds at 5, 10, 20 and 30 days after flowering (DAF) were constructed and used for high-throughput sequencing to identify microRNAs (miRNAs). A total of 235 miRNAs including 114 known conserved miRNAs and 121 novel miRNAs were identified. The expression patterns of these miRNAs in the four libraries were investigated by bioinformatics and quantitative real-time polymerase chain reaction (qPCR) analysis. It was found that several miRNAs, including Lus-miRNA156a was significantly correlated with seed development process. In order to confirm the actual biological function of Lus-miRNA156a, over-expression vector was constructed and transformed to Arabidopsis. The phenotypes of homozygous transgenic lines showed decreasing of oil content and most of the fatty acid content in seeds as well as late flowering time. The results provided a clue that miRNA156a participating the fatty acid biosynthesis pathway and the detailed molecular mechanism of how it regulates the pathway needs to be further investigated.