Vibrio Alginolyticus Infection Research Articles

Mentha piperita powder enhances the biological response, growth performance, disease resistance, and survival of Oreochromis niloticus infected with Vibrio alginolyticus

AbstractRecently, medical plants have been widely used as replacements for antibiotics in disease treatment. Because of its multiple medicinal uses, peppermint (Mentha piperita, MP) is a common herbal remedy. In the present study, MP powder was used as a feed additive to assess growth performance; hematological; biochemical and immune parameters; intestinal histology; and interleukin 1β (IL-1β) gene expression, as well as protection against Vibrio alginolyticus infection in Oreochromis niloticus. O. niloticus (n = 120, 25.66 ± 0.16 g) were fed diets containing 0 (CTR), 2, 3, or 4% MP for 60 days. The results revealed that the inclusion of 2% MP significantly improved the growth indices, intestinal morphological parameters, and reduced the feed conversion ratio. The 2% MP treatment significantly (P < 0.05) increased hematological parameters (red blood cell (RBC) count, white blood cell (WBC) count, packed cell volume% (PCV%), hemoglobin) compared with those of the CTR (P < 0.05). Additionally, feeding fish 2% MP diets decreased the levels of cholesterol and LDL (low-density lipoprotein). There were significant increases in immune responses (serum protein and phagocytic activity and index) and non-significant increases in the expression of IL-1β in the 2% MP group comparing with the other groups and the CTR group (P < 0.05). At the end of the feeding trial (60 days), fish were challenged with a virulent strain of Vibrio alginolyticus and the results showed that the mortality rate decreased in the 2% MP treatment group, followed by the 3% and 4% MP groups. Overall, the results revealed that the dietary inclusion of 2% MP can exhibit growth-promoting and immunostimulant effects for sustainable aquaculture.

LKB1 regulates autophagy through AMPK/TOR signaling pathway to alleviate the damage caused by Vibrio alginolyticus infection

LKB1 (liver kinase B1) is a key upstream kinase of AMPK and plays an important role in various cellular activities. While the function and mechanism of LKB1 have been widely reported in the study of tumor, there are few reports on its role in bacterial infectious diseases, especially in shrimp. In the present study, molecular characterization revealed that LvLKB1 has an open reading frame (ORF) of 1266 bp encoding 421 amino acids with a molecular weight of about 48 KDa, including the kinase region, N-terminal regulatory domain and C-terminal regulatory domain. LvLKB1 in hepatopancreas and hemocytes was significantly upregulated after infection with Vibrio alginolyticus (V. alginolyticus). After silencing LvLKB1 gene in Litopenaeus vannamei (L. vannamei) and artificially infecting V. alginolyticus, the survival rate of L. vannamei was significantly decreased. Subsequently, it was found that the expression of inflammatory factors in hepatopancreas and hemocytes of shrimp was up-regulated, and the expression of lipid oxidation factors was decreased after silencing LKB1, leading to the phenomenon of lipid accumulation in hepatopancreas. In order to explore the mechanism, autophagy levels of shrimp were detected after silencing LKB1, which showed that autophagy levels in hepatopancreas and hemocytes were significantly reduced. Further studies conclusively showed that silencing LvLKB1 inhibited AMPK phosphorylation induced by V. alginolyticus infection, thereby activating TOR pathway and inhibiting autophagy in shrimp. These results indicate that LvLKB1 regulates autophagy through AMPK/TOR signaling pathway to alleviate the damage caused by V. alginolyticus infection.

Oxidative stress, gene expression and histopathology of cultured gilthead sea bream (Sparus aurata) naturally co-infected with Ergasilus sieboldi and Vibrio alginolyticus

BackgroundParasitic and bacterial co-infections have been associated with increasing fish mortalities and severe economic losses in aquaculture through the past three decades. The aim of this study was to evaluate the oxidative stress, histopathology, and immune gene expression profile of gilthead sea bream (Sparus aurata) co-infected with Ergasilus sieboldi and Vibrio alginolyticus.ResultsVibrio alginolyticus and Ergasilus sieboldi were identified using 16 S rRNA and 28 S rRNA sequencing, respectively. The collagenase virulence gene was found in all Vibrio alginolyticus isolates, and the multiple antimicrobial resistance index ranged from 0.286 to 0.857. Oxidant-antioxidant parameters in the gills, skin, and muscles of naturally infected fish revealed increased lipid peroxidation levels and a decrease in catalase and glutathione antioxidant activities. Moreover, naturally co-infected gilthead sea bream exhibited substantial up-regulation of il-1β, tnf-α, and cyp1a1. Ergasilus sieboldi encircled gill lamellae with its second antennae, exhibited severe gill architectural deformation with extensive eosinophilic granular cell infiltration. Vibrio alginolyticus infection caused skin and muscle necrosis in gilthead sea bream.ConclusionThis study described some details about the gill, skin and muscle tissue defense mechanisms of gilthead sea bream against Ergasilus sieboldi and Vibrio alginolyticus co-infections. The prevalence of co-infections was 100%, and no resistant fish were detected. These co-infections imbalance the health status of the fish by hampering the oxidant-antioxidant mechanisms and proinflammatory/inflammatory immune genes to a more detrimental side. Our results suggest that simultaneous screening for bacterial and parasitic pathogens should be considered.

Protective effects of dietary Astragalus polysaccharides on large yellow croaker (Larimichthys crocea) against Vibrio alginolyticus infection

As one of the effective immunopotentiators, Astragalus polysaccharides (APS) are being used widely in prevention and control of fish bacteriosis. However, the understanding of the related immune protection mechanisms is still limited. In this study, the protective effects of dietary APS on large yellow croaker (Larimichthys crocea) following Vibrio alginolyticus infection were investigated. After continuous feeding for 42 d, fish in APS group exhibited higher survival rates against V. alginolyticus infection compared to the control group, and 500 mg/kg APS produced the highest relative percent survival (RPS) of 53.33%, therefore, 500 mg/kg (0.05%) supplementation was recommended in large yellow croaker farming from a standpoint of antibacterial infection. APS could enhance antioxidant level of fish by increasing serum T-AOC capacity and SOD activity and reducing MDA content, and improve innate immune response by increasing serum AKP and ACP activities. Head kidney differential transcriptome analysis between control group and 500 mg/kg APS group before and after V. alginolyticus infection corroborated the effects of APS on activation of antioxidant capacity and innate immunity by up-regulating the antioxidant-related genes and activating CTLR pathway, respectively. Additionally, APS could also activate fish adaptive immunity by reversing V. alginolyticus-induced inhibition on T and B cell receptor signaling pathways. All these findings suggested that APS may exert the protective effects against V. alginolyticus infection by improving antioxidant ability, innate and adaptive immune responses of large yellow croaker, thus providing insights into the protection mechanisms of APS in fish and highlighting their potential application in fish aquaculture.

Exogenous pyruvate promotes gentamicin uptake to kill antibiotic-resistant Vibrio alginolyticus

Elucidating antibiotic resistance mechanisms is necessary for developing novel therapeutic strategies. The increasing incidence of antibiotic-resistant Vibrio alginolyticus infection threatens both human health and aquaculture, but the mechanism has not been fully elucidated. Here, an isobaric tags for relative and absolute quantification (iTRAQ) functional proteomics analysis was performed on gentamicin-resistant V. alginolyticus (VA-RGEN) and a gentamicin-sensitive strain in order to characterize the global protein expression changes upon gentamicin resistance. Then, the bacterial killing assay and bacterial gentamicin pharmacokinetics were performed. Proteomics analysis demonstrated a global metabolic downshift in VA-RGEN, where the pyruvate cycle (the P cycle) was severely compromised. Exogenous pyruvate restored the P cycle activity, disrupting the redox state and increasing the membrane potential. It thereby potentiated gentamicin-mediated killing by approximately 3000- and 150-fold in vitro and in vivo, respectively. More importantly, bacterial gentamicin pharmacokinetics indicated that pyruvate enhanced gentamicin influx to a degree that exceeded the gentamicin expelled by the bacteria, increasing the intracellular gentamicin. Thus, our study suggests a metabolism-based approach to combating gentamicin-resistant V. algonolyticus, which paves the way for combating other types of antibiotic-resistant bacterial pathogens.

Tyramine beta hydroxylase-mediated octopamine synthesis pathway in Litopenaeus vannamei under thermal, salinity, and Vibrio alginolyticus infection stress

Stress responses impact the immune systems, growth, and reproduction of aquatic organisms. Neuroendocrine regulation involving biogenic amines, including octopamine (OA), plays a pivotal role in maintaining physiological balance during stress. This study focuses on the synthesis pathway of OA, particularly the role of tyramine beta hydroxylase (TBH), in Litopenaeus vannamei under stress. TBH catalyzes the conversion of tyramine to OA, a process critical for physiological responses. The present study demonstrated LvTBH at the protein level under different stress conditions during acute (0.5, 1, 2 h) and chronic stress (24, 72, 168 h) periods. LvTBH increased in thoracic ganglia within 2 h under hyperthermal stress, accompanied by elevated OA levels. Conversely, LvTBH decreased in the brain and circumesophageal connective tissues during acute and chronic hypothermal stress. Additionally, LvTBH increased in the brain and circumesophageal connective tissues under acute infection stress, coinciding with elevated OA levels. These findings collectively contribute to a more intricate understanding of the neuroendocrine dynamics within L. vannamei under stress, underscoring the role of TBH in orchestrating responses crucial for adaptation.

Molecular characterization of a cation-dependent mannose-6-phosphate receptor gene in Crassostrea hongkongensis and its responsiveness in Vibrio alginolyticus infection.

The cation-dependent mannose-6-phosphate receptor (CD-M6PR) is a P-type lectin that plays a crucial role in lysosomal enzyme transport, bacterial resistance, and viral entry. In this study, we cloned and analyzed the ORF of the CD-M6PR gene from Crassostrea hongkongensis and named it ChCD-M6PR. We analyzed the nucleotide and amino acid sequence of ChCD-M6PR, its tissue expression pattern and immune response to Vibrio alginolyticus. Our results showed that the ORF of ChCD-M6PR was 801 bp long and encoded a protein of 266 amino acids with a signal peptide at the N-terminus, as well as Man-6-P_recep, ATG27 and transmembrane structural domains. Phylogenetic analysis indicated that Crassostrea hongkongensis shared the highest similarity with Crassostrea gigas in the terms of CD-M6PR. The ChCD-M6PR gene was found to be expressed in various tissues, with the highest expression observed in the hepatopancreas and the lowest in the hemocytes by the fluorescence quantitative PCR. Furthermore, the expression of ChCD-M6PR gene was significantly up-regulated for a short time in response to Vibrio alginolyticus infection in the gill and hemocytes, while it was down-regulated in the gonads. The expression patterns of ChCD-M6PR also varied in the other tissues. The 96h cumulative mortality rate of Crassostrea hongkongensis infected with Vibrio alginolyticus after knockdown the ChCD-M6PR gene was significantly higher. Overall, our findings suggests that ChCD-M6PR plays a crucial role in the immune response of Crassostrea hongkongensis to Vibrio alginolyticus infection, and its tissue-specific expression patterns may be indicatitive of varied immune responses across tissues.

Adenosine 5'-monophosphate-activated protein kinase (AMPK) negatively regulates the immunity and resistance to Vibrio alginolyticus of white shrimp, Penaeus vannamei.

Shrimp immunology is vital in establishing prophylactic and therapeutic strategies for controlling pathological problems that threaten shrimp production. Apart from dietary treatments, the adenosine 5'-monophosphate-activated protein kinase (AMPK), an important regulatory enzyme that restores cellular energy balance during metabolic and physiological stress, is known to have therapeutic potential to improve shrimp's defense mechanism. Despite this, studies targeting the AMPK pathway in shrimp exposed to stressful conditions are vastly limited. In this study, AMPK was knocked down to assess the immunological changes and white shrimp, Penaeus vannamei resistance to Vibrio alginolyticus infection. Shrimps were injected individually and simultaneously with dsRNA targeting specific genes such as AMPK, Rheb, and TOR, after which the hepatopancreas was analyzed for the different gene expressions. The gene expressions of AMPK, Rheb, and TOR were effectively suppressed after being treated with dsRNAs. The Western blot analysis further confirmed a reduction in the protein concentration of AMPK and Rheb in the hepatopancreas. The suppression of AMPK gene led to a robust increase in the shrimp's resistance to V. alginolyticus, whereas the activation of AMPK by metformin decreased the shrimp's disease resistance. Among the mTOR downstream targets, the HIF-1α expression in shrimp treated with dsAMPK significantly increased at 48h but returned to normal levels when shrimp were treated with dsAMPK and either dsRheb or dsTOR. Immune responses such as respiratory burst, lysozyme activity, and phagocytic activity increased, while superoxide dismutase activity decreased following the knockdown of the AMPK gene compared to the control group. However, co-injection with dsAMPK and dsTOR or dsRheb restored immune responses to normal levels. Collectively, these results demonstrate that the inactivation of AMPK may ameliorate shrimp's innate immune response to recognize and defend against pathogens via the AMPK/mTOR1 pathway.

Efficacy of combined inactivated vaccines against Vibrio alginolyticus and Streptococcus agalactiae infections in Nile tilapia in Egypt

Vibrio alginolyticus and Streptococcus agalactiae are important bacterial pathogens that yielded high losses in Nile tilapia in Egypt. The present study aimed to check the protective efficacy of inactivated whole-cell bivalent vaccines against these pathogens using incomplete Freund’s adjuvant and Montanide™ IMS 1312 VG as adjuvants. The antibody titers have been determined at different weeks post-vaccination (WPV). Moreover, the protection levels against the challenged bacterial pathogens have also been examined in relation to the time-dependent protection at different WPV. The results revealed that serum antibodies were generated in all immunized fish at 1st WPV, peaked at 4th WPV, continued, and gradually decreased from 6th WPV to 14th WPV in all vaccinated groups. In addition, vaccines induced significantly higher protection of the immunized tilapia, manifested by higher survival rates. We noticed that the antibody levels and survival rates of the vaccinated fish by a vaccine adjuvanted by Montanide™ IMS 1312 VG were higher than those produced by a vaccine adjuvanted by incomplete Freund’s adjuvant at different time points. Moreover, no external clinical signs, visceral adhesions, or internal lesions were recorded in the vaccinated tilapia, demonstrating the safety of the formulated vaccines. According to the aforementioned findings, we could suggest that the prepared bivalent vaccines, using the two adjuvant types, are safe and highly protective and could be utilized as promising candidate vaccines to increase the resistance of Nile tilapia against V. alginolyticus and S. agalactiae infections. Moreover, Montanide™ IMS 1312 VG enhanced the immuno-protectivity and exhibited optimum immune response and earlier protection compared to the vaccine adjuvanted by incomplete Freund’s adjuvant, demonstrating its added value during the preparation of tilapia vaccines.

Dietary effects of Sanacore® GM on productive performance, immune-antioxidative status, cytokines, and resistance of European sea bass to Vibrio alginolyticus infection

ABSTRACT This study examined the dietary effects of Sanacore®GM (SAN) on growth and production, immune-antioxidative status, cytokines, and the resistance of European sea bass to Vibrio alginolyticus infection. Fish (28.5–32.3 g) were fed on 0.0, 1.0, 2.0, 4.0, 6.0, and 8.0 g SAN/kg feed for ten weeks. Following that, fish were intraperitoneally injected with V. alginolyticus, and observed for further ten days. Among different water quality parameters, only unionized ammonia and nitrite values were significantly declined in groups received 4.0–8.0 g SAN/kg feed. Significant increases in fish growth, production, hematological, and immune-antioxidant indices were observed in SAN-fed fish. Compared with the control group, IL-1β and TNF-α genes expressions were down-regulated in groups fed on 4.0–8.0 g SAN/kg feed. After bacterial infection, low fish mortalities (20%–10%) were observed in fish fed with 4.0–8.0 g SAN/feed, respectively. The polynomial fitting curve demonstrates that the optimum SAN level for European sea bass is 5.0 g/kg feed.

Antibacterial effects of curcuma (Curcuma xanthorriza) on Vibrio alginolyticus in baramundi

This study aimed to determine the inhibitory power of the growth of Vibrio alginolyticus bacteria, phytochemicals, and the effectiveness of Curcuma rhizome extract against the prevention of Vibrio alginolyticus infection in white snapper. The research was conducted in January - July 2022 at Malikussaleh University. The research method consists of the preparation of curcuma extract, preparation of Vibrio alginolyticus bacteria, inhibition zone test, preparation of test biota, application of Curcuma extract through immersion in fish, challenge test of Vibrio alginolyticus, and fish rearing. The research design used was a Complete Randomized Design (RAL)-Non-Factorial. The study consisted of 2 stages, namely (1) antibacterial test of rhizome extract against Vibrio alginolyticus, with the treatment of aromatic ginger, Curcuma, zingiber rhizome extracts at doses of A (60%), B (80%), and C (100%), respectively. The results showed that Curcuma rhizome extract is the best. The results of phytochemical tests showed that the Curcuma rhizome plant was positive for flavonoids, tannins, alkaloids, saponins, terpenoids, and phenolics, but negative for steroid compounds. So continued the Phase 2 study with the aim of testing the effectiveness of temulawak rhizome extract at doses: A (70%), B (80%), C (90%), and D (100%). The results of the phase 2 study showed that the most effective concentration in inhibiting the growth of Vibrio alginolyticus bacteria is temulawak rhizomes with a concentration of 100%. Rated survival rate 86.67%), duration of healing (24 hours 28 minutes), and percentage of recovery from white snapper (86.7%).

High temperature aggravates mortalities of the Pacific oyster (Crassostrea gigas) infected with Vibrio: A perspective from homeostasis of digestive microbiota and immune response

Long-lasting high temperature and bacterial exposure are two critical environmental factors contributing to the mass mortality of oysters in summer. In this study, we investigated the effects of high-temperature exposure and Vibrio alginolyticus infection on the mortality of the Pacific oysters, Crassostrea gigas. The results of survival experiment demonstrated that the overall survival of Vibrio-infected oysters was significantly reduced at high-temperature stress. The 16S rRNA amplicon sequencing showed that high temperature significantly disrupted the structure of the infected oyster's digestive gland microbiota and increased the abundance of potentially pathogenic bacteria. Transcriptome profiling showed that expression of critical genes associated with inflammation was suppressed in the early phase of infection but was induced in the later phase. In contrast, genes related to apoptosis and oxidative stress were continuously upregulated, indicating that homeostasis of inflammatory response was maintained in the early phase but was eventually destroyed upon continuous high temperature exposure. This work is of practical significance for deciphering the cause of oyster mortality in summer and monitoring disease outbreaks in the oyster culture.

Effects of a Commercial Feed Additive (Sanacore® GM) on Immune-Antioxidant Profile and Resistance of Gilthead Seabream (Sparus aurata) Against Vibrio alginolyticus Infection

Abstract The effects of a functional additive (Sanacore® GM; SAN) on immune and antioxidant indices, and the resistance of gilthead seabream (Sparus aurata) against Vibrio alginolyticus infection were investigated. For this, four diets containing 0% (the control), 0.1%, 0.2%, and 0.4% SAN were offered to triplicated groups of fish (20–23 g) for ten weeks. Subsequently, fish were injected intraperitoneally with V. alginolyticus and monitored for further ten days. Feeding the fish on SAN-supplemented diets showed positive effects on leukocyte counts and its differential percentages. Serum lysozyme activity and total immunoglobulin values, as well as blood phagocytic activity and indices, were linearly and quadratically higher in SAN-fed fish, especially at the 0.4% SAN diet. Similarly, linear and quadratic increases in catalase, superoxide dismutase, and total antioxidant capacity were observed in SAN-fed fish, particularly at the 0.4% SAN diet. Conversely, malondialdehyde values decreased in SAN-fed fish compared with the control group, which showed its highest value. The highest expression of the IL-1β gene coupled with the lowest TNF-α and HSP70 genes expressions was found in the fish fed with the 0.4% SAN. On the other hand, fish fed on the control diet showed the lowest IL-1β gene coupled with the highest TNF-α and HSP70 genes expressions. After bacterial infection, most of the control fish died with a relative percent of survival of 5.0%; meanwhile feeding gilthead seabream on SAN-enriched diets significantly enhanced their protection against V. alginolyticus infection fed on the 0.4% SAN diet showed 100% survival. The SAN administration to gilthead seabream especially at the 0.4% level led to significant promotions in antioxidative and immune responses and augmented the fish resistance to V. alginolyticus infection.

Molecular cloning and characterization of NLRX1 from orange-spotted grouper (Epinephelus coioides) as a mediator of ROS production through its LRR domains

NLRX1, an intracellular immune receptor, negatively modulates the proinflammatory signals and also regulates immune cell metabolic function in human. However, in teleost, there is limited understanding of molecular mechanisms that how NLRX1 interacts with the host immune system. This research cloned and identified NLRX1 from orange-spotted grouper (Epinephelus coioides). The cDNA contains a 2889 bp open reading frame (ORF) which encodes 962 amino acids, including three typical (a N-terminal, a NACHT and five leucine-rich repeat (LRR)) domains. The EcNLRX1 protein presents a mitochondrial localization and shows highly constitutive expression in mitochondria-rich tissues. Reactive oxygen species (ROS) are mainly generated in mitochondria to induce cellular oxidative stress. EcNLRX1 could potently induce ROS generation. After Vibrio alginolyticus infection, EcNLRX1 mRNA expression in spleen is greatly increased in the early stage (24 h and 48 h, p < 0.001) of immune response. Under Poly I:C stimulation, EcNLRX1 synergistically triggers ROS release. And the EcNLRX1-LRR domain is a key structural domain for ROS activation. In summary, this result indicated that teleost NLRX1 is a critical component in controlling innate immune responses and oxidative stress at mitochondria, which provides a novel insight for understanding of fish immunometabolism.

The hematopoietic cytokine Astakine play a vital role in hemocyte proliferation and innate immunity in Scylla paramamosain

Astakine may induce hematopoietic response in crustaceans, as it is necessary for hemocyte proliferation. In this study, we produced the recombinant Scylla paramamosain Astakine (rspAstakine) and assessed its immunomodulatory function. We analyzed its amino acid sequences and generated a three-dimensional model, then ligand binding sites and enzyme commission of spAstakine were predicted. The rspAstakine was identified at 21.3 kDa by Western blot and liquid chromatography-mass spectrometry. The results showed that rspAstakine induced proliferation of hemocytes in mud crab in vivo and in vitro. The expression of immune-related genes was up-regulated after rspAstakine treatment, similarly to the immunity-related parameters, activities of superoxide dismutase, phenoloxidase, lysozyme, and peroxidase. Additionally, the intracellular content of reactive oxygen species was higher in the rspAstakine treatment group than PBS group. The rspAstakine also enhanced the rate of phagocytosis, while reduced the apoptosis rate of hemocytes after Vibrio alginolyticus infection. The mortalities of the V. alginolyticus only group and rspAstakine + V. alginolyticus group were 83.3 % and 58.3 %, respectively, which illustrated that rspAstakine plays a protective role against V. alginolyticus infection in S. paramamosain. Our results demonstrate the potential of Astakine to enhance the proliferation and immunomodulatory function of hemocytes in crustaceans.

Molecular characterization and functional roles for Vibrio alginolyticus resistance of an octopamine/tyramine receptor of the white shrimp, Litopenaeus vannamei

Octopamine and Tyramine are biogenic amines that have been demonstrated to play an important immunological role in white shrimp, Litopenaeus vannamei. G protein-coupled receptors, known as seven-transmembrane domain receptors, are a variety of neurotransmitter receptors which are sensitive to biogenic amines for initiating the cell signaling pathway. In present study, we cloned and characterized an octopamine/tyramine receptor (LvOA/TA-R) from the hemocytes of L. vannamei, with a 1194 b.p. open reading frame that encodes 398 amino acids. Several bioinformatics analyses indicated that LvOA/TA-R had seven conserved hydrophobic transmembrane domains. The phylogenetic analysis and multiple sequence alignment indicated that LvOA/TA-R was orthologous to the OA/TA receptor of tiger shrimp, P. monodon. LvOA/TA-R was expressed in hemocytes and nervous tissue including circumoesphageal connective tissue and the thoracic and abdominal ganglia. Significant increases in LvOA/TA-R occurred in hemocytes of L. vannamei under Vibrio alginolyticus infection within 30–60 min of infection. Here, we demonstrated that LvOA/TA-R expression is upregulated in response to Vibrio alginolyticus infection and appears to be functionally responsible for the observed immune response. These results suggest that LvOA/TA-R mediates regulation of immunity, which promotes the resistance of L. vannamei to V. alginolyticus.

Transcriptome profiling of the Pacific oyster (Crassostrea gigas) suggests distinct host immune strategy in response to Vibrio alginolyticus infection

Bacterial infection is a serious challenge for oysters, which brings various disease problems to oyster culture. To better understand the immune response to bacterial infection, we performed RNA-seq to profile the transcriptome of gill tissue in the Pacific oyster (Crassostrea gigas) at short-term (6 h) and long-term (48 h) stages after Vibrio alginolyticus infection. A total of 1534 and 2483 differentially expressed genes (DEGs) were identified at short- and long-term stages after infection, respectively. Gene ontology (GO) analysis showed that the identified DEGs were significantly enriched in GO terms of stress response, ion transport, signal transduction and other biological processes. Notably, we observed that the immune strategy was altered in the C. gigas in response to Vibrio infection. In the short-term stage, most of the immune-related genes in C. gigas were down-regulated, and the immune response was low and may be suppressed. While in the long-term stage, large-scale immune-related genes associated with ion channels were activated and immune system was boosted. Distinct sets of immune-related genes with different functions were identified at short-term and long-term stages. Differences in these genes suggested the alteration of immune strategy in the C. gigas in response to Vibrio infection. This work provides valuable resources for better understanding of immune response to bacterial infection and will be important for disease monitoring and disease resistance breeding in the oysters.

Integrative analysis of the miRNA–mRNA regulation network in hemocytes of Penaeus vannamei following Vibrio alginolyticus infection

Penaeus vannamei is an important cultured shrimp that has high commercial value in the worldwide. However, the industry suffers heavy economic losses each year due to disease outbreaks caused by pathogenic bacteria. In the present study, after Vibrio alginolyticus infection, DNA damage in the hemocytes of the shrimp markedly increased, and autophagy and apoptosis increased significantly. Subsequently, hemocytes were sampled from the control and infected shrimp and sequenced for mRNA and microRNA (miRNA) 24 h after V. alginolyticus infection to better understand the response mechanism to bacterial infection in P. vannamei. We identified 1,874 and 263 differentially expressed mRNAs (DEGs) and miRNAs (DEMs) respectively, and predicted that 997 DEGs were targeted by DEMs. These DEGs were involved in the regulation of multiple signalling pathways, such as Toll and IMD signalling, TGF-beta signalling, MAPK signalling, and cell apoptosis, during Vibrio alginolyticus infection of the shrimp. We identified numerous mRNA-miRNA interactions, which provide insight into the defense mechanism that occur during the antimicrobial process of P. vannamei.

Molecular characterization, expression and functional analysis of large yellow croaker (Larimichthys crocea) peroxisome proliferator-activated receptor gamma

The peroxisome proliferator-activated receptor gamma (PPARγ) are nuclear receptors with distinct roles in energy metabolism and immunity. Although extensively studied in mammals, immunomodulatory roles of this molecule in teleost fish remain to be investigated. In this study, large yellow croaker (Larimichthys crocea) PPARγ (LcPPARγ) sequence was cloned, which encodes a polypeptide of 541 amino acids that include signature domains belonging to the nuclear receptor superfamily. Phylogenetically, LcPPARγ was most closely related to PPARγ derived from European sea bass (Dicentrarchus labrax). Quantitative analysis shown a ubiquitous expression of this molecule, with highest expression level detected in the intestine. The expression of LcPPARγ was decreased in the intestine, muscle, body kidney, spleen and head kidney-derived monocytes/macrophages (MO/MФs) over the course of Vibrio alginolyticus (V. alginolyticus) infection. In contrast, an up-regulation of LcPPARγ was observed in head kidney-derived MO/MФs following docosahexaenoic acid (DHA) treatment. This increase in LcPPARγ leads to an up-regulation of LcCD11b and LcCD18 and an enhancement of complement-mediated phagocytosis. Furthermore, cytokine secretions of V. alginolyticus-stimulated MO/MФs were modulated following LcPPARγ activations that up-regulated the expression of LcIL-10, while decreased the expression of LcIL-1β, LcTNF-α and LcTGF-β1. Overall, our results indicated that LcPPARγ plays a role in regulating functions of MO/MФs and likely contribute to MO/MФs polarization.

Characterization of large yellow croaker (Larimichthys crocea) osteoprotegerin and its role in the innate immune response against to Vibrio alginolyticus.

Osteoprotegerin (OPG) is a member of the tumor necrosis factor receptor superfamily, contributing to inflammation, apoptosis, and differentiation. However, the function of OPG in the host immune system of teleosts remains unclear. Here, we cloned the cDNA of the LcOPG gene from large yellow croaker. LcOPG mRNA was expressed in all analyzed tissues and was upregulated by Vibrio alginolyticus infection in immune tissues and monocytes/macrophages (MO/MФ). Subsequently, the LcOPG protein was expressed and purified using a prokaryotic expression system. Recombinant LcOPG protein (rLcOPG) treatment suppressed V. alginolyticus-induced pro-inflammatory cytokine and enhanced V. alginolyticus-induced anti-inflammatory cytokine mRNA expression. Furthermore, rLcOPG decreased V. alginolyticus-induced MO/MФ apoptosis. Therefore, the results indicate that LcOPG might play a role in the immune response of V. alginolyticus-infected large yellow croaker.