Studies on immunological characteristics and transcriptomic analysis of Litopenaeus vannamei low salt-tolerance family.

Litopenaeus vannamei is a widely distributed euryhaline aquatic animal, affected by low salinity, which can impact its disease resistance and immunity. However, there is a limited understanding of the adaptation mechanisms of L. vannamei with different genetic backgrounds to low salinity. Therefore, the present study aimed to compare the immunity characteristics and transcriptomics of L. vannamei low salt-tolerant (FG I/J) and low salt-sensitive (control) families. Also, the disease resistance and immune parameters (including [THC], hemolymph cell viability, lysozyme activity [LZM], phenoloxidase content [PO], interleukin-6 [IL-6], and tumor necrosis factor-alpha [TNF-α]) of the FG I/J and control families of L. vannamei under low salinity (5‰) and ambient salinity (24‰) were examined. Additionally, hepatopancreas transcriptomics of the FG I/J and control families were analyzed at a salinity of 5‰. The results showed that the FG I/J family had higher disease resistance to Vibrio parahaemolyticus and stronger immunological capacity than the control family. Transcriptomic analysis showed significantly enriched energy metabolism and immune regulation pathways. Therefore, we speculated that energy metabolism provides sufficient energy for immunological modulation in the FG I/J family to deal with long-term low-salt stress and achieve high growth and survival rates.

Two colistin resistance-producing Aeromonas strains, isolated from coastal waters in Zhejiang, China: characteristics, multi-drug resistance and pathogenicity.

Introduction: Aeromonas spp. are ubiquitous inhabitants of ecosystems, and many species are opportunistically pathogenic to humans and animals. Multidrug-resistant (MDR) Aeromonas species have been widely detected in hospitals, urban rivers, livestock, and aquatic animals. Results: In this study, we identified two Aeromonas isolates, namely Aeromonas veronii 0728Q8Av and Aeromonas caviae 1029Y16Ac, from coastal waters in Zhejiang, China. Both isolates exhibited typical biochemical characteristics and conferred MDR to 11 kinds of antibiotics, remaining susceptible to ceftazidime. Whole-genome sequencing revealed that both isolates harbored multiple antibiotic resistance genes (ARGs) and several mobile genetic elements (MGEs) on the chromosomes, each containing a resistance genomic island (GI), a typical class 1 integron, a transposon, and various insertion sequences (ISs). Most ARGs were situated within the multiple resistance GI, which contained a class 1 integron and a transposon in both Aeromonas isolates. Furthermore, a chromosomal mcr-3.16 gene was identified in A. veronii 0728Q8Av, while a chromosomal mcr-3.3 was found in A. caviae 1029Y16Ac. Both mcr-3 variants were not located within but were distanced from the multidrug resistance GI on the chromosome, flanking by multiple ISs. In addition, a mcr-3-like was found adjacent to mcr-3.16 to form a tandem mcr-3.16-mcr-3-like-dgkA structure; yet, Escherichia coli carrying the recombinants of mcr-3-like did not exhibit resistance to colistin. And an incomplete mcr-3-like was found adjacent to mcr-3.3 in A. caviae 1029Y16Ac, suggesting the possibility that mcr-3 variants originated from Aeromonas species. In vivo bacterial pathogenicity test indicated that A. veronii 0728Q8Av exhibited moderate pathogenicity towards infected ayu, while A. caviae 1029Y16Ac was non-virulent. Discussion: Thus, both Aeromonas species deserve further attention regarding their antimicrobial resistance and pathogenicity.

Zebrafish nos2a benefits bacterial proliferation via suppressing ROS and inducing NO production to impair the expressions of inflammatory cytokines and antibacterial genes.

The enzyme nitric oxide synthase 2 or inducible NOS (NOS2), reactive oxygen species (ROS) and nitric oxide (NO) are important participants in various inflammatory and immune responses. However, the functional significances of the correlations among piscine NOS2, ROS and NO during pathogen infection remain unclear. In teleost, there are two nos2 genes (nos2a and nos2b). It has been previously reported that zebrafish nos2a behaves as a classical inducible NOS, and nos2b exerts some functions similar to mammalian NOS3. In the present study, we reported the functional characterization of zebrafish nos2a during bacterial infection. We found that zebrafish nos2a promoted bacterial proliferation, accompanied by an increased susceptibility to Edwardsiella piscicida infection. The nagative regulation of zebrafish nos2a during E. piscicida infection was characterized by the impaired ROS levels, the induced NO production and the decreased expressions of proinflammatory cytokines, antibacterial genes and oxidant factors. Furthermore, although both inducing ROS and inhibiting NO production significantly inhibited bacterial proliferation, only inhibiting NO production but not inducing ROS significantly increased resistance to E. piscicida infection. More importantly, ROS supplementation and inhibition of NO completely abolished this detrimental consequence mediated by zebrafish nos2a during E. piscicida infection. All together, these results firstly demonstrate that the innate response mediated by zebrafish nos2a in promoting bacterial proliferation is dependent on the lower ROS level and higher NO production. The present study also reveals that inhibition of NO can be effective in the protection against E. piscicida infection.

Toxicities of polystyrene microplastics (MPs) and hexabromocyclododecane (HBCD), alone or in combination, to the hepatopancreas of the whiteleg shrimp, Litopenaeus vannamei.

The hepatopancreas is one of the largest organs playing crucial roles in metabolism and detoxification in crustacean invertebrates. Although toxicities have been increasingly documented for the two ubiquitous pollutants, hexabromocyclododecane (HBCD) and microplastics (MPs), in model animals, little is known about their impacts on the hepatopancreas of crustaceans. To fill this knowledge gap, the effects of MPs and HBCD, alone or in combination, on the hepatopancreas were evaluated in a commercially important crustacean species (the whiteleg shrimp) by histological observation as well as quantification of hepatic lesion-, metabolism-, and detoxification-related parameters. In addition, to reveal potential mechanisms underlying the hepatoxicity observed, the accumulation of HBCD in the shrimp and the status of oxidative stress were also investigated. Our results demonstrated that exposure of the whiteleg shrimp to MPs and HBCD for 4 weeks resulted in evident histological injury in the hepatopancreas and marked elevation in hepatic lesion markers (alanine aminotransferase and aspartate aminotransferase) in the hemolymph. Moreover, both metabolism (activity of phosphofructokinase, contents of lactic acid and adenosine triphosphate, and expression of metabolism-related genes) and detoxification (contents of cytochrome P450, UDP-glucuronosyltransferase, and glutathione, activity of glutathione S-transferase, and expression of detoxification-related genes) were found to be disrupted by the pollutants tested. In addition, exposure to MPs and HBCD also led to alterations in the contents and/or activities of antioxidant enzymes and resulted in oxidative damage to the hepatopancreas (indicated by marked elevation in malondialdehyde content). Furthermore, a significant amount of HBCD accumulated in shrimp treated with HBCD-containing seawater. The data also illustrated that HBCD-MP coexposure was more toxic than single exposure to these pollutants. These findings suggest that MPs and HBCD may exert hepatotoxic impacts on whiteleg shrimp by accumulating in vivo and inducing oxidative stress, which could pose a severe threat to the health of this important crustacean species.

Impacts of dietary supplementation of bamboo vinegar and charcoal powder on growth performance, intestinal morphology, and gut microflora of large-scale loach Paramisgurnus dabryanus.

Although accumulating data demonstrate that dietary supplementation of bamboo vinegar and charcoal powder (BVC) can significantly strengthen the immunity and boost the growth of domestic animals, its application potency still awaits verification in commercial fish species such as the large-scale loach Paramisgurnus dabryanus. The impacts of 90-day dietary supplementation of 1% and 2% BVC on survival and growth performance of the loach, and on the intestinal morphological characteristics and gut microflora were analyzed. Our data show that the large-scale loach supplied with BVC at the experimental doses had significant higher survival rates and better growth performance (indicated by greater weight gain (1.13-1.14 times), higher specific growth rate (1.04 times), and lower feed conversion ratio (0.88-0.89 times)) compared to that of the control (P<0.05). Histological examination revealed significant longer villus (3.22-5.54 times), deeper crypt (1.77-1.87 times), and thicker muscle (1.59-3.17 times) in the intestines of large-scale loach fed with BVC (P<0.05). Furthermore, we found that the gut microflora consisted of significantly fewer proportions of potential pathogenic bacterial species (Aeromonas veronii and Escherichia coli), but significantly greater proportions of beneficial microbes (Lactococus raffinolactis and Faecalibacterium prausnitzii). Therefore, dietary intake of BVC can promote intestinal tract development and optimize gut microflora, by which the survival and growth of large-scale loach may be improved.

Microplastics and bisphenol A hamper gonadal development of whiteleg shrimp (Litopenaeus vannamei) by interfering with metabolism and disrupting hormone regulation.

Gonadal development is a prerequisite for the reproductive success of an organism, and might be affected by environmental factors such as emergent pollutants. Although marine crustaceans are threatened by ubiquitous emergent pollutants such as microplastics (MPs) and bisphenol A (BPA) under realistic scenarios, studies about the impacts of these pollutants on the gonadal development of crustacean species are rare. In this study, the effects of MPs and BPA, alone or in combination, on gonadal development were investigated in whiteleg shrimp (Litopenaeus vannamei). The results obtained demonstrated that whiteleg shrimp exposed to MPs and BPA had significantly smaller gonad-somatic index (GSI) and an obvious delay in the gonad developmental stage. In addition, exposure of whiteleg shrimp to pollutants tested resulted in a reduction in the oxygen consumption rate, elevation in the ammonia excretion rate, decline in the O: N ratio, and downregulation in the expression of metabolism-related genes, indicating significant disruptions of shrimp metabolism by the pollutants. Furthermore, in addition to a few exceptions, both the in vivo contents of gonadal development-related hormones (GIH and MIH) and the expression of genes encoding regulatory hormones (GIH, MIH, and CHH) were upregulated by the exposure of whiteleg shrimp to the pollutants investigated, suggesting a significant obstruction of endocrine regulation. Moreover, MP-BPA coexposure was shown to be more toxic to whiteleg shrimp than the corresponding single exposures and significantly greater amount of BPA accumulated in the gonads (both testis and ovaries) of shrimp with the coexistence of MPs, which may be caused by the Trojan horse effect and summation of the toxic impacts on common targets. In general, the data obtained in this study demonstrated that MPs and BPA at environmentally realistic concentrations significantly inhibited the gonadal development of whiteleg shrimp probably by interfering with metabolism and disrupting endocrine regulation.

A real-time LAMP-based dual-sample microfluidic chip for rapid and simultaneous detection of multiple waterborne pathogenic bacteria from coastal waters.

Waterborne pathogens are becoming a serious worldwide health hazard; thus, the regular monitoring of epidemic pathogens is urgently required for public safety. In the present study, we developed a microfluidic chip integrated loop-mediated isothermal amplification technique (on-chip LAMP) to simultaneously detect 10 waterborne pathogenic bacteria, Campylobacter jejuni, Listeria monocytogenes, Salmonella enterica, Shigella flexneri, Staphylococcus aureus, Vibrio alginolyticus, V. cholerae, V. parahemolyticus, V. vulnificus, and Yersinia enterocolitica. This method was capable of simultaneously completing 22 genetic analyses of two specimens and achieved limits of detection ranging from 7.92 × 10-3 to 9.54 × 10-1 pg of genomic DNA of pure bacteria per reaction. The processes from sample loading to microfluidic operation were in a highly automated format, and the LAMP reaction ran to completion within 35 minutes, with a minimal volume of 22 µl per each half of a single chip. The coefficient of variation for the time-to-positive value was less than 0.1, indicating an excellent reproducibility of the dual-sample on-chip LAMP assay. The clinical sensitivity and specificity in analyses of coastal water samples were 93.1% and 98.0%, respectively, in comparison with traditional microbiological methods. Our established dual-sample on-chip LAMP assay provides an effective multiple-pathogen analysis of waterborne bacterial pathogens. This indicates that the method is applicable for on-site detection and routine monitoring of waterborne bacteria in aquatic environments.

Cloning, characterization, and transcriptional activity of ß-actin promoter of African catfish (Clarias gariepinus).

Selection of suitable promoters is crucial for the efficient expression of exogenous genes in transgenic animals. Although one of the most effective promoters, the ß-actin promoter, has been widely studied in fish species, it still remains unknown in the economical important African catfish (Clarias gariepinus). In this study, the ß-actin promoter of African catfish (cgß-actinP) was cloned and characterized. In addition, recombinant plasmid pcgß-actinP-EGFP with enhanced green fluorescent protein (GFP) gene as the reporter gene was constructed to verify the transcriptional activity. We obtained a cgß-actinP fragment length of 1405 bp, consisting 104 bp of the 5' proximal promoter, 96 bp of the first exon, and 1205 bp of the first intron. Similar to those of other fish species, cgß-actinP contains three key transcription regulatory elements (CAAT box, CArG motif, and TATA box). GFP-specific fluorescent signals were detected in chicken embryonic fibroblasts cells (DF-1 cells) transfected with pcgß-actinP-EGFP, which was approximately 1.11 times of the positive control. In addition, GFP was effectively expressed in zebrafish larvae microinjected with linearized cgß-actinP-EGFP, with expression rate reaching approximately 49.84%. Our data indicate that cgß-actinP could be a potential candidate promoter in the practice of constructing "all fish" transgenic fish.

A novel antiviral coumarin derivative as a potential agent against WSSV infection in shrimp seedling culture.

White spot syndrome virus (WSSV), a double-stranded DNA virus that infects crustaceans, is the most serious viral pathogen affecting shrimp farming worldwide. To reduce the economic losses caused by WSSV, we screened a novel coumarin derivative from a small molecule drug library, N-(4-((4-(((2-oxo-2H-chromen-7-yl)oxy)methyl)-1H-1,2,3-triazol-1-yl)sulfonyl)phenyl)acetamide (N2905), to evaluate its anti-WSSV effects in vivo. We determined that compound N2905, up to a concentration of 20 mg/L, significantly decreased the number of WSSV copies in Litopenaeus vannamei post-larvae, with a maximum inhibitory rate of > 90 %, and increased the survival rate of WSSV-infected post-larvae. Pre-treatment and post-treatment assays indicated that N2905 could treat, but not prevent, WSSV infections. When WSSV was preincubated with N2905 for 1-4 h, the incidence of viral infections was significantly reduced and survival time of post-larvae extended to 120 h. A stability study of N2905 provided a reference for its practical use. Considering the antiviral stability of N2905 in culture water within 2 d, continuous N2905 exchange was performed, showing a significant decrease in viral load at 120 h post-infection (hpi) and a 55 % increase in survival of WSSV-infected post-larvae. Overall, our study demonstrated the potential of N2905 as an antiviral agent.

Simultaneous detection of multiple bacterial and viral aquatic pathogens using a fluorogenic loop-mediated isothermal amplification-based dual-sample microfluidic chip.

Rapid and user-friendly diagnostic tests are necessary for early diagnosis and immediate detection of diseases, particularly for on-site screening of pathogenic microorganisms in aquaculture. In this study, we developed a dual-sample microfluidic chip integrated with a real-time fluorogenic loop-mediated isothermal amplification assay (dual-sample on-chip LAMP) to simultaneously detect 10 pathogenic microorganisms, that is Aeromonas hydrophila, Edwardsiella tarda, Vibrio harveyi, V. alginolyticus, V. anguillarum, V. parahaemolyticus, V. vulnificus, infectious hypodermal and haematopoietic necrosis virus, infectious spleen and kidney necrosis virus, and white spot syndrome virus. This on-chip LAMP provided a nearly automated protocol that can analyse two samples simultaneously, and the tests achieved limits of detection (LOD) ranging from 100 to 10-1  pg/µl for genomic DNA of tested bacteria and 10-4 to 10-5  pg/µl for recombinant plasmid DNA of tested viruses, with run times averaging less than 30 min. The coefficient of variation for the time-to-positive value was less than 10%, reflecting a robust reproducibility. The clinical sensitivity and specificity were 93.52% and 85.53%, respectively, compared to conventional microbiological or clinical methods. The on-chip LAMP assay provides an effective dual-sample and multiple pathogen analysis, and thus would be applicable to on-site detection and routine monitoring of multiple pathogens in aquaculture.

Comparable Ecological Processes Govern the Temporal Succession of Gut Bacteria and Microeukaryotes as Shrimp Aged.

Understanding the rules that govern the successions of gut microbiota is prerequisite for testing general ecological theories and sustaining a desirable microbiota. However, the ignorance of microeukaryotes raises the question of whether gut microeukaryotes are assembled according to the same rules as bacteria. We tracked the shrimp gut bacterial and microeukaryotic communities by a longitudinal dense sampling. The successions of both domains were significantly correlated with host age, with relatively stable microeukaryotic communities in adult shrimp. Gut microeukaryotes exhibited significantly higher turnover rate, but fewer transient species, lower proportion of temporal generalists, and narrower habitat niche breadth than bacteria. The γ-diversity partitioning analysis revealed that the successions of gut microbiotas were primarily ascribed to the high dissimilarity as shrimp aged ([Formula: see text]IntraTimes), whereas the relative importance of [Formula: see text]IntraTimes was significantly higher for microeukaryotes than that for bacteria. Compared with contrasting ecological processes in governing free-living bacteria and microeukaryotes, the ecological patterns were comparable between host-associated gut counterparts. However, the gut microeukaryotes were governed more strongly by deterministic selection relative to nestedness compared with the gut bacteria, which supports the "size-plasticity" hypothesis. Our results highlight the importance of independently interpreting free-living and host-associated meta-communities for a comprehensive understanding of the processes that govern microbial successions.

Bacterial Community Dynamics During Nursery Rearing of Pacific White Shrimp (Litopenaeus vannamei) Revealed via High-Throughput Sequencing.

A 20-day trial was conducted to reveal bacterial community dynamics in a commercial nursery of larval Litopenaeus vannamei larvae. The bacterial communities in the ambient water were profiled by high-throughput sequencing of the V4-V5 hypervariable region of the 16S rRNA gene. The results indicated that the dominant bacterial phyla between the metamorphosis stage and postlarval stage were Bacteroidetes, Proteobacteria, Cyanobacteria, and Firmicutes, representing more than 80.09% of the bacterial operational taxonomic units. The relative abundance among bacterial phyla notably differed between the two stages. The relative abundance of Cyanobacteria was higher in the metamorphosis stage, while that of Bacteroidetes was higher and more stable in the postlarval stage. At the class level, the relative abundance of Sphingobacteriia and Alphaproteobacteria increased markedly in the postlarval stage, while that of Flavobacteriia decreased. Redundancy analysis showed that bacterial composition in the metamorphosis stage was positively correlated with salinity, alkalinity, and pH, while in the postlarval stage, it was positively correlated with ammonium nitrogen and nitrite nitrogen. Thus, microbial community diversity in the nursery phase varies per rearing stage.

Exogenous Ca2+ mitigates the toxic effects of TiO2 nanoparticles on phagocytosis, cell viability, and apoptosis in haemocytes of a marine bivalve mollusk, Tegillarca granosa.

Phagocytosis suppression induced by nanoparticles (NPs) exposure is increasingly reported in marine species. However, the mechanisms underlying this impact remain poorly understood. In order to improve our present understanding of the immunotoxicity of NPs, acute (96 h) TiO2 NP exposure and rescue trials via exogenous supply of Ca2+ were performed in the blood clam, Tegillarca granosa. The results show that the phagocytosis rate, cell viability, and intracellular Ca2+ concentration of haemocytes were significantly suppressed, whereas the intracellular ROS concentration of haemocytes significantly increased upon nTiO2 exposure. Exposure to nTiO2 also led to the significant downregulation of Caspase-3, Caspase-6, apoptosis regulator Bcl-2, Bcl-2-associated X, calmodulin kinase II, and calmodulin kinase kinase II. Furthermore, the toxic impacts of nTiO2 were partially mitigated by the addition of exogenous Ca2+, as indicated by the recovery tendency in almost all the measured parameters. The present study indicates that Ca2+ signaling could be one of the key pathways through which nTiO2 attacks phagocytosis.

Ageing reduces the reproductive performance of male white shrimp Litopenaeus vannamei by altering sperm intracellular Ca2+ concentrations and interfering with sperm apoptosis.

Although the effects of age on the reproductive performance of various invertebrates, including white shrimp Litopenaeus vannamei are increasingly well documented, the mechanisms manifesting these impacts remain poorly understood. To ascertain the mechanisms of age on reproductive performance, the sperm quality, intracellular contents of Ca2+, insemination and hatching rates, and status of sperm apoptosis in terms of the expression of key regulatory genes were investigated in 11 and 16 month old male L. vannamei. The aged male individuals (16 months) had lesser reproductive performance in terms of fertilization and hatching rates. In addition, fewer and less viable sperm were detected in aged shrimp, which may be due to the altered expression of apoptosis-related genes. Furthermore, the aged males had lesser intracellular contents of Ca2+ in the sperm which may decrease the capacity of these gametes to undergo a complete acrosome reaction. In general, due to the decrease in intracellular contents of Ca2+ and alterations in the process of apoptosis, aged L. vannamei have relatively lesser quality sperm and may, therefore, have lesser reproductive performance.

The synergic impacts of TiO2 nanoparticles and 17ß-estradiol (E2) on the immune responses, E2 accumulation, and expression of immune-related genes of the blood clam, Tegillarca granosa.

The extensive use of TiO2 nanoparticles (nTiO2) in industrial products has led to their release into the marine environment, thereby posing a potential risk to marine organisms. However, in addition to affecting marine organisms through its inherent properties, nTiO2 can also act as a vehicle for other toxic pollutants due to their strong adsorption ability through the "Trojan horse" effect. Due to their potential hazard, the endocrine disrupting chemicals (EDCs) such as 17ß-estradiol (E2), have been considered as one of the most serious anthropogenic threats to biodiversity and ecosystem health. However, there is still a lack of knowledge regarding the possible synergistic effects of nTiO2 and endocrine disrupting chemicals (EDCs) on marine organisms to date. Therefore, the combined effects of nTiO2 and 17ß-estradiol (E2) on the immune responses of the blood clam, Tegillarca granosa, were investigated in this study. After 10 days of treatment, the total number, phagocytic activity, red granulocytes ratio, and the phagocytosis of hemocytes were significantly reduced in almost all treatment groups. Furthermore, expressions of genes from NFκß and Toll-like receptor signaling pathways were significantly altered after exposure to nTiO2 and/or E2, indicating a reduced sensitivity to pathogen challenges. In addition, compared to exposure to E2 alone, co-exposure to E2 and nTiO2 led to a significant increase in the content of alkali-labile phosphate (ALP) in hemolymph, suggesting an enhanced E2 bioconcentration in the presence of nTiO2. In general, the present study demonstrated that nTiO2 enhanced the immunotoxicity of E2 to the blood clam, which may be due to the increased E2 uptake in the presence of nTiO2.

Ocean Acidification Affects the Cytoskeleton, Lysozymes, and Nitric Oxide of Hemocytes: A Possible Explanation for the Hampered Phagocytosis in Blood Clams, Tegillarca granosa.

An enormous amount of anthropogenic carbon dioxide (CO2) has been dissolved into the ocean, leading to a lower pH and changes in the chemical properties of seawater, which has been termed ocean acidification (OA). The impacts of pCO2-driven acidification on immunity have been revealed recently in various marine organisms. However, the mechanism causing the reduction in phagocytosis still remains unclear. Therefore, the impacts of pCO2-driven OA at present and near-future levels (pH values of 8.1, 7.8, and 7.4) on the rate of phagocytosis, the abundance of cytoskeleton components, the levels of nitric oxide (NO), and the concentration and activity of lysozymes (LZM) of hemocytes were investigated in a commercial bivalve species, the blood clam (Tegillarca granosa). In addition, the effects of OA on the expression of genes regulating actin skeleton and nitric oxide synthesis 2 (NOS2) were also analyzed. The results obtained showed that the phagocytic rate, cytoskeleton component abundance, concentration and activity of LZM of hemocytes were all significantly reduced after a 2-week exposure to the future OA scenario of a pH of 7.4. On the contrary, a remarkable increase in the concentration of NO compared to that of the control was detected in clams exposed to OA. Furthermore, the expression of genes regulating the actin cytoskeleton and NOS were significantly up-regulated after OA exposure. Though the mechanism causing phagocytosis seemed to be complicated based on the results obtained in the present study and those reported previously, our results suggested that OA may reduce the phagocytosis of hemocytes by (1) decreasing the abundance of cytoskeleton components and therefore hampering the cytoskeleton-mediated process of engulfment, (2) reducing the concentration and activity of LZM and therefore constraining the degradation of the engulfed pathogen through an oxygen-independent pathway, and (3) inducing the production of NO, which may negatively regulate immune responses.

Different concentrations of Edwardsiella tarda ghost vaccine induces immune responses in vivo and protects Sparus macrocephalus against a homologous challenge.

Bacterial ghosts (BGs) can be generated by the controlled expression of the PhiX174 lysis gene E in gram-negative bacteria. They are intriguing vaccine candidates since ghosts retain functional antigenic cellular determinants often lost during traditional inactivation procedures. Here we prepared Edwardsiella tarda ghost (ETG) and tested different concentrations in vaccination trials. The results showed that serum IgM antibody titers were significantly higher in three different concentration immunization groups than control group (P < 0.05), However, there was no significant (P > 0.05) difference between the immunized groups. The phagocytic percentage (PP) was significantly higher (P < 0.05) in ETG immunized groups than in the control group from 3 days post-treatment. The PP continued to rise with time until day 21, when the values of three ETG immunized groups were 45.7%,51.2% and 50.7%, respectively. In addition, phagocytic index (PI) was significantly higher (P < 0.05) in ETG immunized groups than in the control group after 7 days post-treatment. However, there was no significant (P > 0.05) difference of PP or PI between immunized groups. In addition, non-specific immune immunity, such as acid phosphatase, alkaline phosphatase, superoxide dismutase and lysozyme activities displayed a similar pattern in all immunized groups, all immunized fish showed significantly higher activities than control group fish (P < 0.05). Most importantly three ETG immunized groups were all significantly more protected against the E. tarda challenge (19/25, 76% survival), (21/25, 84% survival) and (20/25, 80% survival) respectively, compared to (9/25, 36% survival) survival in the control group, but there was no significant (P > 0.05) difference of survival rate (SR) or relative percent survival (RPS) between immunized groups. All these results suggest that an ETG could stimulate cellular and humoral immunity, and could be used as a vaccine candidate in S.m. In summary, ETG can protect fish from Edwardsiellosis, and there is no significant difference in SR and RPS when three different concentrations of ETG are used, so it can easily be developed as a vaccine for mechanical and artificial operations.

Laboratory simulation reveals significant impacts of ocean acidification on microbial community composition and host-pathogen interactions between the blood clam and Vibrio harveyi.

It has been suggested that climate change may promote the outbreaks of diseases in the sea through altering the host susceptibility, the pathogen virulence, and the host-pathogen interaction. However, the impacts of ocean acidification (OA) on the pathogen components of bacterial community and the host-pathogen interaction of marine bivalves are still poorly understood. Therefore, 16S rRNA high-throughput sequencing and host-pathogen interaction analysis between blood clam (Tegillarca granosa) and Vibrio harveyi were conducted in the present study to gain a better understanding of the ecological impacts of ocean acidification. The results obtained revealed a significant impact of ocean acidification on the composition of microbial community at laboratory scale. Notably, the abundance of Vibrio, a major group of pathogens to many marine organisms, was significantly increased under ocean acidification condition. In addition, the survival rate and haemolytic activity of V. harveyi were significantly higher in the presence of haemolymph of OA treated T. granosa, indicating a compromised immunity of the clam and enhanced virulence of V. harveyi under future ocean acidification scenarios. Conclusively, the results obtained in this study suggest that future ocean acidification may increase the risk of Vibrio pathogen infection for marine bivalve species, such as blood clams.

Molecular characterization of a cDNA encoding Na+/K+/2Cl- cotransporter in the gill of mud crab (Scylla paramamosain) during the molt cycle: Implication of its function in osmoregulation.

Although iono-regulatory processes are critical for survival of crustaceans during the molt cycle, the mechanisms involved are still not clear. The Na+/K+/2Cl- cotransporter (NKCC), a SLC12A family protein that transports Na+, K+ and 2Cl- into cells, is essential for cell ionic and osmotic regulation. To better understand the role of NKCC in the molt osmoregulation, we cloned and characterized a NKCC gene from the mud crab, Scylla paramamosain (designated as SpNKCC). The predicted SpNKCC protein is well conserved, and phylogenetic analysis revealed that this protein was clustered with crustacean NKCC. Expression of SpNKCC was detected in all the tissues examined but was highest in the posterior gills. Transmission electron microscopy revealed that posterior gills had a thick type of epithelium for ion regulation while the anterior gills possessed a thin phenotype related to gas exchange. During the molting cycle, hemolymph osmolality and ion concentrations (Na+ and Cl-) increased significantly over the postmolt period, remained stable in the intermolt and premolt stages and then decreased at ecdysis. Meanwhile, the expression of SpNKCC mRNA was significantly elevated (26.7 to 338.8-fold) at the ion re-establishing stages (postmolt) as compared with baseline molt level. This pattern was consistent with the coordinated regulation of Na+/K+-ATPase α-subunit (NKA α), carbonic anhydrase cytoplasmic (CAc) isoform and Na+/H+ exchanger (NHE) genes in the posterior gills. These data suggest that SpNKCC may be important in mediating branchial ion uptake during the molt cycle, especially at the postmolt stages.

[Expression of Edwardsiella tarda luxS gene at different growth stage].

OBJECTIVE: Purpose of this work was to explore the distribution of LuxS/AI-2 quorum sensing system in Edwardsiella, and analyze expression characteristics and biological function of the key gene luxS accompanying the growth of Edwardsiella. METHODS: The full-length of AI-2/LuxS of Edwardsiella tarda was cloned by PCR based on the sequence on NCBI, then characteristics and conservative structure of this protein-coding gene were analyzed using web database and bioinformatics tools. The anti-rabbits serum was prepared after this protein was purified through prokaryotic expression. The expression level of luxS gene was analyzed during different growth stages using Western blot and further the distribution of luxS gene in Edwardsiella tarda was studied by this technique. To explore whether the specific LuxS is AI-2 dependent we used the method of antibody neutralization to analyze the effect of the anti-rabbits serum on the growth of Edwardsiella tarda. RESULTS] The luxS gene was obtained by PCR, its length was 516 bp, and the sequence was highly conserved in Edwardsiella tarda. Results of Western blot analysis showed that LuxS expression level was the lowest in the lag phase and began increasing when entered index phase. It reached the peak in the late index phase and decreased in decline phase. Moreover, Antibody neutralization results showed that, it can elongate the growth plateau phase, but it has no significant effect on bacterial growth. CONCLUSION: The key gene of luxS was highly conserved, and LuxS/AI-2 was widely distributed among Edwardsiella tarda. The expression level of luxS gene was different during every growth period, expression of LuxS protein reached the highest level in the late index phase.