Portal of entry for pathogenic Vibrio alginolyticus into large yellow croaker Pseudosciaena crocea, and characteristics of bacterial adhesion to mucus

Effect of Pomacea canaliculata on Limnodrilus hoffmeisteri: Behavior, Oxidative Stress, and Microbiota Alterations

Pomacea canaliculata is an invasive species which has significantly impacted native ecosystems globally. The benthic worm Limnodrilus hoffmeisteri is essential for the stability of the native aquatic ecosystem, facilitating the nutrient cycle dynamics through bioturbation. Nevertheless, limited information exists regarding the impact of P. canaliculata on those key native benthic species. Present study evaluated the impacts of P. canaliculata on L. hoffmeisteri by exposing L. hoffmeisteri to P. canaliculata (PC group) and the native snail Bellamya aeruginosa (BA group), with a control group consisting of no snails (NS group). The survival rate of L. hoffmeisteri in the PC group persisted diminished over 14 days, with notable declines in the rates of successful food acquisition and aggregation, an increase in migration, and a decrease in swing frequency. Elevated oxidative stress levels were linked to these alterations in L. hoffmeisteri behavior. Additionally, the presence of P. canaliculata increased the abundance of intestinal pathogenic bacteria in L. hoffmeisteri, with Aeromonas being one of the most lethal. Experimental models of Aeromonas-free P. canaliculata (AFPC), re-infected AFPC (IPC), and Aeromonas (As) were established to illustrate the role of Aeromonas in the decline of L. hoffmeisteri. Similar patterns in L. hoffmeisteri survival, behavior, and oxidative stress were observed in As, IPC, and PC group; however, these effects were mitigated by the elimination of Aeromonas in the AFPC group. Furthermore, L. hoffmeisteri was fatally affected by the four Aeromonas strains that were obtained from P. canaliculata intestine. These findings indicate that P. canaliculata exerts a deleterious impact on L. hoffmeisteri, and Aeromonas colonizing in intestine plays an important role. This study reveals a novel invasion mechanism of P. canaliculata.

A novel small non-coding RNA 562 mediates the virulence of Pseudomonas plecoglossicida by regulating the expression of fliP, a key component of flagella T3SS

Pseudomonas plecoglossicida is a vital pathogen that poses a substantial risk to aquaculture. Small RNAs (sRNAs) are non-coding regulatory molecules capable of sensing environmental changes and modulating virulence-associated signaling pathways, such as the assembly of flagella. However, the relevant researches on P. plecoglossicida are an urgent need. Here, we report a novel sRNA, sRNA562, which has potential to regulate the post-transcriptional of fliP, a key component of the lateral flagellar type III secretion system. In this study, the effects of sRNA562 on the virulence of P. plecoglossicida and its role in regulating the pathogenic process were investigated through the use of a constructed sRNA562 deletion strain. The deletion of sRNA562 resulted in an up-regulation of fliP in P. plecoglossicida, and leading to increased swarming motility and enhanced the ability of biofilm formation, adhesion and chemotaxis. Subsequent artificial infection experiment demonstrated that the deletion of sRNA562 increased the virulence of P. plecoglossicida towards hybrid grouper, as evidenced by a reduction in survival rate, elevation of tissue bacterial load, and the exacerbation of histopathological damage. Further studies have found that the deletion of sRNA562 lead to an up-regulation of fliP expression during hybrid grouper infection, thereby enhancing bacterial swarming ability and ultimately heightening pathogenicity, leading to a dysregulated host response to infection, tissue damage and eventually death. Our work revealed a sRNA that exerts negative regulation on the expression of lateral flagella in P. plecoglossicida, thereby impacting its virulence. These findings provide a new perspective on the virulence regulation mechanism of P. plecoglossicida, contributing to a more comprehensive understanding in the field of pathogenicity research.

Transcriptomic analysis of Vibrio alginolyticus challenged by Rhizoma coptidis reveals mechanisms of virulence genes

Rhizoma coptidis, a Chinese herbal medicine widely used to treat various bacterial infections, has the potential to develop antibiotic substitutes to overcome the drug resistance of Vibrio alginolyticus. To study the inhibitory effect of R. coptidis on V. alginolyticus, we sequenced the transcriptomes of three groups of samples of wild-type V. alginolyticus (CK) and V. alginolyticus, which were stressed by 5 mg/mL R. coptidis for 2 h (RC_2 h) and 4 h (RC_4 h). CK was compared with RC_2 h and RC_4 h, respectively, and a total of 1565 differentially expressed genes (DEGs) (988 up-regulated and 577 down-regulated) and 1737 DEGs (1152 up-regulated and 585 down-regulated) were identified. Comparing RC_2 h with RC_4 h, 156 DEGs (114 up-regulated and 42 down-regulated) were identified. The ability of biofilm formation and motility of V. alginolyticus altered upon with different concentrations of R. coptidis. Interestingly, relative expression patterns of virulence genes appeared statistically significantly varied, upon different concentrations of R. coptidis extract. DEGs were annotated to the Gene Ontology (GO) database for function enrichment analysis and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, the results showed that the main enriched pathways, was those related to the virulence of V. alginolyticus. This study provides a new perspective for understanding the complex pathogenic mechanism of V. alginolyticus. R. coptidis could potnetially be used as alternative or complimnetary to antibiotics to treat infections after further research.

Variations and Interseasonal Changes in the Gut Microbial Communities of Seven Wild Fish Species in a Natural Lake with Limited Water Exchange during the Closed Fishing Season

The gut microbiota of fish is crucial for their growth, development, nutrient uptake, physiological balance, and disease resistance. Yet our knowledge of these microbial communities in wild fish populations in their natural ecosystems is insufficient. This study systematically examined the gut microbial communities of seven wild fish species in Chaohu Lake, a fishing-restricted area with minimal water turnover, across four seasons. We found significant variations in gut microbial community structures among species. Additionally, we observed significant seasonal and regional variations in the gut microbial communities. The Chaohu Lake fish gut microbial communities were predominantly composed of the phyla Firmicutes, Proteobacteria(Gamma), Proteobacteria(Alpha), Actinobacteriota, and Cyanobacteria. At the genus level, Aeromonas, Cetobacterium, Clostridium sensu stricto 1, Romboutsia, and Pseudomonas emerged as the most prevalent. A co-occurrence network analysis revealed that C. auratus, C. carpio, and C. brachygnathus possessed more complex and robust gut microbial networks than H. molitrix, C. alburnus, C. ectenes taihuensis, and A. nobilis. Certain microbial groups, such as Clostridium sensu stricto 1, Romboutsia, and Pseudomonas, were both dominant and keystone in the fish gut microbial network. Our study offers a new approach for studying the wild fish gut microbiota in natural, controlled environments. It offers an in-depth understanding of gut microbial communities in wild fish living in stable, limited water exchange natural environments.

The Pleiotropic Phenotypes Caused by an hfq Null Mutation in Vibrio harveyi

Hfq is a global regulator and can be involved in multiple cellular processes by assisting small regulatory RNAs (sRNAs) to target mRNAs. To gain insight into the virulence regulation of Hfq in Vibrio harveyi, the hfq null mutant, ∆hfq, was constructed in V. harveyi strain 345. Compared with the wild-type strain, the mortality of pearl gentian sharply declined from 80% to 0% in ∆hfq when infected with a dose that was 7.5-fold the median lethal dose (LD50). Additionally, ∆hfq led to impairments of bacterial growth, motility, and biofilm formation and resistance to reactive oxygen species, chloramphenicol, and florfenicol. A transcriptome analysis indicated that the expression of 16.39% genes on V. harveyi 345 were significantly changed after the deletion of hfq. Without Hfq, the virulence-related pathways, including flagellar assembly and bacterial chemotaxis, were repressed. Moreover, eleven sRNAs, including sRNA0405, sRNA0078, sRNA0419, sRNA0145, and sRNA0097, which, respectively, are involved in chloramphenicol/florfenicol resistance, outer membrane protein synthesis, electron transport, amino acid metabolism, and biofilm formation, were significantly down-regulated. In general, Hfq contributes to the virulence of V. harveyi 345 probably via positively regulating bacterial motility and biofilm formation. It is involved in flagellar assembly and bacterial chemotaxis by binding sRNAs and regulating the target mRNAs.

Role of the melanocortin system in zebrafish skin physiology

The agouti-signaling protein (ASIP) acts as both a competitive antagonist and inverse agonist of melanocortin receptors which regulate dorsal-ventral pigmentation patterns in fish. However, the potential role of ASIP in the regulation of additional physiological pathways in the skin is unknown. The skin plays a crucial role in the immune function, acting as a physical limitation against infestation and also as a chemical barrier due to its ability to synthesize and secrete mucus and many immune effector proteins. In this study, the putative role of ASIP in regulating the immune system of skin has been explored using a transgenic zebrafish model overexpressing the asip1 gene (ASIPzf). Initially, the structural changes in skin induced by asip1 overexpression were studied, revealing that the ventral skin of ASIPzf was thinner than that of wild type (WT) animals. A moderate hypertrophy of mucous cells was also found in ASIPzf. Histochemical studies showed that transgenic animals appear to compensate for the lower number of cell layers by modifying the mucus composition and increasing lectin affinity and mucin content in order to maintain or improve protection against microorganism adhesion. ASIPzf also exhibit higher protein concentration under crowding conditions suggesting an increased mucus production under stressful conditions. Exposure to bacterial lipopolysaccharide (LPS) showed that ASIPzf exhibit a faster pro-inflammatory response and increased mucin expression yet severe skin injures and a slight increase in mortality was observed. Electrophysiological measurements show that the ASIP1 genotype exhibits reduced epithelial resistance, an indicator of reduced tissue integrity and barrier function. Overall, not only are ASIP1 animals more prone to infiltration and subsequent infections due to reduced skin epithelial integrity, but also display an increased inflammatory response that can lead to increased skin sensitivity to external infections.

Function of the rpoD gene in Pseudomonas plecoglossicida pathogenicity and Epinephelus coioides immune response

Pseudomonas plecoglossicida is a Gram-negative pathogenic bacterium that causes visceral white spot disease in several marine fish species, resulting in high mortality and financial loss. Based on previous RNA sequencing (RNA-seq) results, rpoD gene expression is significantly up-regulated in P. plecoglossicida during infection, indicating that rpoD may contribute to bacterial pathogenicity. To investigate the role of this gene, five specific short hairpin RNAs (shRNAs) were designed and synthesized based on the rpoD gene sequence, with all five mutants exhibiting a significant decrease in rpoD gene expression in P. plecoglossicida. The mutant with the highest silencing efficiency (89.2%) was chosen for further study. Compared with the wild-type (WT) P. plecoglossicida strain NZBD9, silencing rpoD in the rpoD-RNA interference (RNAi) strain resulted in a significant decrease in growth, motility, chemotaxis, adhesion, and biofilm formation in P. plecoglossicida. Silencing of rpoD also resulted in a 25% increase in the survival rate, a one-day delay in the onset of death, and a significant decrease in the number of white spots on the spleen surface of infected orange-spotted groupers (Epinephelus coioides). In addition, rpoD expression and pathogen load were significantly lower in the spleens of E. coioides infected with the rpoD-RNAi strain than with the WT strain of P. plecoglossicida. We performed RNA-seq of E. coioides spleens infected with different P. plecoglossicida strains. Results showed that rpoD silencing in P. plecoglossicida led to a significant change in the infected spleen transcriptomes. In addition, comparative transcriptome analysis showed that silencing rpoD caused significant changes in complement and coagulation cascades and the IL-17 signaling pathway. Thus, this study revealed the effects of the rpoD gene on P. plecoglossicida pathogenicity and identified the main pathway involved in the immune response of E. coioides.

The Adhesion and Spoilage of Shewanella putrefaciens in Tilapia

Shewanella putrefaciens is a typical spoilage bacteria organism in seafood. The adhesion ability of three S. putrefaciens strains (HR-15, JR-18, HC-71) isolated from putrefied tilapia were evaluated by mucus adhesion in vitro and intestinal adhesion in vivo. The results of the spoilage of the inoculated fish fillets and spoilage of the refrigerated fish both showed that the adhesion ability of S. putrefaciens was positively correlated with the spoilage ability. High-throughput sequencing and GC-MS results showed that S. putrefaciens with high adhesion ability also significantly changed the intestinal flora of fish, causing an increase in the intestinal bacteria such as Plesionomas, Macellibacteroides, Acinetobacter, and Legionella, which then led to the increase in volatile substances such as low-grade aldehydes, alcohols, and ketones in the fish, serious fatty acid oxidation, and excitement of the fishy smell.

Spoilage of tilapia by Pseudomonas putida with different adhesion abilities

Four Pseudomonas putida strains isolated from spoiled tilapia were divided into three adhesion abilities—high, medium, and low—by an in vitro mucus model. Four strains had no significant difference in spoilage ability to the inoculated fish fillets. However, according to the in vivo experiment, the spoilage caused by the four P.putida was positively correlated with their adhesion abilities. High adhesion strains not only caused more TVB-N in chilled fish, but also activated the spoilage activity of intestinal flora. The diversity of intestinal flora and the changes in volatile components in fish were detected by high-throughput sequencing and SPME-GC/MS. The strains with high adhesion abilities significantly changed the intestinal flora, which led to a significant increase in low-grade aldehydes, indole, and esters in flesh of fish, as well as the production of a fishy and pungent odor. The intestinal adhesion ability of spoilage bacteria was considered the key factor in spoilage of chilled fish.

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A positive correlation between the intestinal adhesion ability of P.putida and the spoilage ability in vivo.

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P.putida affected the intestinal microflora and led to increase in fishy and pungent odor.

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The intestinal adhesion ability of P.putida was considered as a key factor in spoilage.

Effect of Ferredoxin Receptor FusA on the Virulence Mechanism of Pseudomonas plecoglossicida

Pseudomonas plecoglossicida is an aerobic Gram-negative bacterium, which is the pathogen of “Visceral white spot disease” in large yellow croaker. P. plecoglossicida is a temperature-dependent bacterial pathogen in fish, which not only reduces the yield of large yellow croaker but also causes continuous transmission of the disease, seriously endangering the healthy development of fisheries. In this study, a mutant strain of fusA was constructed using homologous recombination technology. The results showed that knockout of P. plecoglossicida fusA significantly affected the ability of growth, adhesion, and biofilm formation. Temperature, pH, H₂O₂, heavy metals, and the iron-chelating agent were used to treat the wild type of P. plecoglossicida; the results showed that the expression of fusA was significantly reduced at 4°C, 12°C, and 37°C. The expression of fusA was significantly increased at pH 4 and 5. Cu²⁺ has a significant inducing effect on the expression of fusA, but Pb²⁺ has no obvious effect; the expression of fusA was significantly upregulated under different concentrations of H₂O₂. The expression of the fusA gene was significantly upregulated in the 0.5~4-μmol/l iron-chelating agent. The expression level of the fusA gene was significantly upregulated after the logarithmic phase. It was suggested that fusA included in the TBDR family not only was involved in the transport of ferredoxin but also played important roles in the pathogenicity and environment adaptation of P. plecoglossicida.

Longitudinal sampling of external mucosae in farmed European seabass reveals the impact of water temperature on bacterial dynamics

Fish microbiota are intrinsically linked to health and fitness, but they are highly variable and influenced by both biotic and abiotic factors. Water temperature particularly limits bacterial adhesion and growth, impacting microbial diversity and bacterial infections on the skin and gills. Aquaculture is heavily affected by infectious diseases, especially in warmer months, and industry practices often promote stress and microbial dysbiosis, leading to an increased abundance of potentially pathogenic bacteria. In this regard, fish mucosa health is extremely important because it provides a primary barrier against pathogens. We used 16 rRNA V4 metataxonomics to characterize the skin and gill microbiota of the European seabass, Dicentrarchus labrax, and the surrounding water over 12 months, assessing the impact of water temperature on microbial diversity and function. We show that the microbiota of external mucosae are highly dynamic with consistent longitudinal trends in taxon diversity. Several potentially pathogenic genera (Aliivibrio, Photobacterium, Pseudomonas, and Vibrio) were highly abundant, showing complex interactions with other bacterial genera, some of which with recognized probiotic activity, and were also significantly impacted by changes in temperature. The surrounding water temperature influenced fish microbial composition, structure and function over time (days and months). Additionally, dysbiosis was more frequent in warmer months and during transitions between cold/warm months. We also detected a strong seasonal effect in the fish microbiota, which is likely to result from the compound action of several unmeasured environmental factors (e.g., pH, nutrient availability) beyond temperature. Our results highlight the importance of performing longitudinal studies to assess the impact of environmental factors on fish microbiotas.

Isolation and enzyme bioprospection of bacteria associated to Bruguiera cylindrica, a mangrove plant of North Sumatra, Indonesia

Mangrove-associated bacteria are of industrial interest due to their diverse and versatile enzyme properties. This study investigates the culturable bacteria from a wide range of habitat in a Bruguiera cylindrica mangrove ecosystem in North Sumatra. Screening of extracellular hydrolytic enzymes showed multiple potential traits in amylase, cellulase, chitinase, phosphatase, protease, and urease production by bacterial isolates. Molecular identification based on 16S rDNA region of a potential strain, Vibrio alginolyticus Jme3-20 is then reported as a newly proteolytic agent. The strain also showed a stable growth under salinity (NaCl) stress with considerable phosphate solubilization activities. Protease activity was enhanced by optimizing the 0.5 % (w/v) sucrose and soy peptone in the fermentation medium. SDS-PAGE and zymogram analysis showed the presence of a 35-kDa MW protease. Hence, our study revealed important insights into the bacterial diversity and activity in mangrove ecosystems, evidencing the importance of microbial exploration in this ecosystem.

pH-Controlled Release of Antigens Using Mesoporous Silica Nanoparticles Delivery System for Developing a Fish Oral Vaccine

The development of effective vaccines and delivery systems in aquaculture is a long-term challenge for controlling emerging and reemerging infections. Cost-efficient and advanced nanoparticle vaccines are of tremendous applicability in prevention of infectious diseases of fish. In this study, dihydrolipoamide dehydrogenase (DLDH) antigens of Vibrio alginolyticus were loaded into mesoporous silica nanoparticles (MSN) to compose the vaccine delivery system. Hydroxypropyl methylcellulose phthalate (HP55) was coated to provide protection of immunogen. The morphology, loading capacity, acid-base triggered release were characterized and the toxicity of nanoparticle vaccine was determined in vitro. Further, the vaccine immune effects were evaluated in large yellow croaker via oral administration. In vitro studies confirmed that the antigen could be stable in enzymes-rich artificial gastric fluid and released under artificial intestinal fluid environment. In vitro cytotoxicity assessment demonstrated the vaccines within 120 μg/ml have good biocompatibility for large yellow croaker kidney cells. Our data confirmed that the nanoparticle vaccine in vivo could elicit innate and adaptive immune response, and provide good protection against Vibrio alginolyticus challenge. The MSN delivery system prepared may be a potential candidate carrier for fish vaccine via oral administration feeding. Further, we provide theoretical basis for developing convenient, high-performance, and cost-efficient vaccine against infectious diseases in aquaculture.

Age-Related Differences in Molecular Profiles for Immune Checkpoint Blockade Therapy

Immune checkpoint blockade (ICB) therapies have significantly improved the prognosis and shown considerable promise for cancer therapy; however, differences in ICB treatment efficacy between the elderly and young are unknown. We analyzed the studies enrolled in the meta-analysis using the deft approach, and found no difference in efficacy except melanoma patients receiving anti–PD-1 therapy. Similarly, higher treatment response rate and more favorable prognosis were observed in elderly patients in some cancer types (e.g., melanoma) with data from published ICB treatment clinical trials. In addition, we comprehensively compared immunotherapy-related molecular profiles between elderly and young patients from public trials and The Cancer Genome Atlas (TCGA), and validated these findings in several independent datasets. We discovered a divergent age-biased immune profiling, including the properties of tumors (e.g., tumor mutation load) and immune features (e.g., immune cells), in a pancancer setting across 27 cancer types. We believe that ICB treatment efficacy might vary depending on specific cancer types and be determined by both the tumor internal features and external immune microenvironment. Considering the high mutational properties in elderly patients in many cancer types, modulating immune function could be beneficial to immunotherapy in the elderly, which requires further investigation.

cheA, cheB, cheR, cheV, and cheY Are Involved in Regulating the Adhesion of Vibrio harveyi

Diseases caused by Vibrio harveyi lead to severe economic losses in the aquaculture industry. Adhesion is an important disease-causing factor observed in bacteria with chemotactic activity. In our study, we measured the adhesion of V. harveyi by subjecting the bacteria to stress using Cu²⁺, Pb²⁺, Hg²⁺, and Zn²⁺. The genes responsible for chemotaxis (cheA, cheB, cheR, cheV, and cheY), which are also crucial for adhesion, were identified and silenced via RNAi. We observed that a decrease in chemotactic gene expression reduced the ability of the organism to demonstrate adhesion, motility, chemotaxis, and biofilm formation. Upon comparing the cheA-RNAi bacteria to the wild-type strain, we observed that the transcriptome of V. harveyi was significantly altered. Additionally, the expression of key genes and the adhesion ability were affected by the pH (pH of 5, 6, 7, 8, and 9), salinity (NaCl at concentrations of 0.8, 1.5, 2.5, 3.5, or 4.5%), and temperature (4, 15, 28, 37, and 44°C) of the medium. Based on these results, the following conclusions were made: (1) The chemotactic genes cheA, cheB, cheR, cheV, and cheY may regulate the adhesion ability of V. harveyi by affecting bacterial motility, and participate in the regulation of adhesion at different temperatures, salinities, and pH values; (2) stable silencing of cheA could alter the transcriptional landscape of V. harveyi and regulate the expression of genes associated with its adhesion mechanisms.

Gut-Liver Immune Response and Gut Microbiota Profiling Reveal the Pathogenic Mechanisms of Vibrio harveyi in Pearl Gentian Grouper (Epinephelus lanceolatus × E. fuscoguttatus )

Vibrio harveyi causes vibriosis in nearly 70% of grouper (Epinephelus sp.), seriously limiting grouper culture. As well as directly inhibiting pathogens, the gut microbiota plays critical roles in immune homeostasis and provides essential health benefits to its host. However, there is still little information about the variations in the immune response to V. harveyi infection and the gut microbiota of grouper. To understand the virulence mechanism of V. harveyi in the pearl gentian grouper, we investigated the variations in the pathological changes, immune responses, and gut bacterial communities of pearl gentian grouper after exposure to differently virulent V. harveyi strains. Obvious histopathological changes were detected in heart, kidney, and liver. In particular, nodules appeared and huge numbers of V. harveyi cells colonized the liver at 12 h postinfection (hpi) with highly virulent V. harveyi. Although no V. harveyi was detected in the gut, the infection simultaneously induced a gut-liver immune response. In particular, the expression of 8 genes associated with cellular immune processes, including genes encoding inflammatory cytokines and receptors, and pattern recognition proteins, was markedly induced by V. harveyi infection, especially with the highly virulent V. harveyi strain. V. harveyi infection also induced significant changes in gut bacterial community, in which Vibrio and Photobacterium increased but Bradyrhizobium, Lactobacillus, Blautia, and Faecalibaculum decreased in the group infected with the highly virulent strain, with accounting for 82.01% dissimilarity. Correspondingly, four bacterial functions related to bacterial pathogenesis were increased by infection with highly virulent V. harveyi, whereas functions involving metabolism and genetic information processing were reduced. These findings indicate that V. harveyi colonizes the liver and induces a gut-liver immune response that substantially disrupts the composition of and interspecies interactions in the bacterial community in fish gut, thereby altering the gut-microbiota-mediated functions and inducing fish death.

Characterization of a cell density-dependent sRNA, Qrr, and its roles in the regulation of the quorum sensing and metabolism in Vibrio alginolyticus

Vibrio alginolyticus is an important fish pathogen causing pandemic diseases in marine animals. Small noncoding RNAs (sRNAs) are important posttranscriptional modulators of gene expression and involved in the pathogenesis of bacterial pathogens. Thus far, no cell density-dependent sRNA has been reported in V. alginolyticus. In this study, a cell density-dependent sRNA, Qrr, predicted based on the previous RNA-Seq analysis of V. alginolyticus cultured at low cell density (LCD) and high cell density (HCD), was characterized. The Qrr mutant showed significantly impaired growth and decreased swimming and swarming ability, and increased biofilm formation, extracellular polysaccharide content, serine protease production, and LD₅₀ values during zebrafish infection in contrast to the wild-type strain. Qrr modulates the master regulators LuxR and AphA in quorum sensing (QS) pathways possibly at the posttranscriptional level by base pairing with the 5'-untranslated regions (5'-UTRs). Meanwhile, both LuxR and AphA could directly bind to the promoter of qrr to activate or repress its transcription, respectively. Moreover, our unbiased metabolic approaches revealed that Qrr modulates a large quantity of metabolic and lipidomic pathways, including amino acids, purine and pyrimidine derivatives, tricarboxylic acid cycle (TCA cycle) intermediates, and lipids. Collectively, this work contributes to a systematic understanding of regulatory roles of the cell density-dependent sRNA, Qrr, in V. alginolyticus.

Virulence-associated genes and antibiotic resistance patterns of Vibrio spp. isolated from cultured marine fishes in Malaysia

Background

Vibriosis is an important bacterial disease of cultured marine fishes worldwide. However, information on the virulence and antibiotic resistance of Vibrio spp. isolated from fish are scarce. This study investigates the distribution of virulence associated genes and antibiotic resistance patterns of Vibrio spp. isolated from cage-cultured marine fishes in Malaysia.

Results

A total of 63 Vibrio spp. isolated from 62 cultured marine fishes in various geographical regions in Peninsular Malaysia were analysed. Forty-two of the isolates (66.7%) were positive for all chiA, luxR and vhpA, the virulence genes produced by pathogenic V. harveyi. A total of 62 Vibrio isolates (98%) had tlh gene of V. parahaemolyticus, while flaC gene of V. anguillarum was detected in 43 of isolates (68%). Other virulence genes, including tdh, trh, hlyA and toxR_vc were absent from any of the isolates. Multiple antibiotic resistance (MAR) was exhibited in all strains of Harveyi clade, particularly against ampicillin, penicillin, polypeptides, cephems and streptomycin. The MAR index ranged between 0.06 and 0.56, and 75% of the isolates have MAR index of higher than 0.20. Host species and geographical origin showed no correlation with the presence of virulence genes and the antibiotic resistance patterns of Vibrio spp.

Conclusions

The study indicates that majority of Vibrio spp. isolated from cultured marine fishes possess virulence genes, but were not associated with human pathogen. However, the antibiotics resistance is a real concern and warrants ongoing surveillance. These findings represent an updated knowledge on the risk of Vibrio spp. to human health, and also provides valuable insight on alternative approaches to combat vibriosis in cultured fish.

Vibriosis in Fish: A Review on Disease Development and Prevention

Current growth in aquaculture production is parallel with the increasing number of disease outbreaks, which negatively affect the production, profitability, and sustainability of the global aquaculture industry. Vibriosis is among the most common diseases leading to massive mortality of cultured shrimp, fish, and shellfish in Asia. High incidence of vibriosis can occur in hatchery and grow-out facilities, but juveniles are more susceptible to the disease. Various factors, particularly the source of fish, environmental factors (including water quality and farm management), and the virulence factors of Vibrio, influence the occurrence of the disease. Affected fish show weariness, with necrosis of skin and appendages, leading to body malformation, slow growth, internal organ liquefaction, blindness, muscle opacity, and mortality. A combination of control measures, particularly a disease-free source of fish, biosecurity of the farm, improved water quality, and other preventive measures (e.g., vaccination) might be able to control the infection. Although some control measures are expensive and less practical, vaccination is effective, relatively cheap, and easily implemented. In this review, the latest knowledge on the pathogenesis and control of vibriosis, including vaccination, is discussed.

Comparing the effect of sucrose gel and metronidazole gel in treatment of clinical symptoms of bacterial vaginosis: a randomized controlled trial

BACKGROUND

Lactobacilli, as normal vaginal flora, have a central role in controlling body environment and preventing the growth of pathogens. Sucrose, by promoting the growth of Lactobacilli, accelerates the suppression of pathogenic bacteria. The aim of this research was to compare the effects of sucrose gel with those of metronidazole gel in treating women with bacterial vaginosis (BV).

METHODS

This triple-blind clinical trial (IRCT2016112631105N1) was conducted with 70 sexually active, premenopausal women diagnosed with bacterial vaginosis through meeting at least three out of four Amsel criteria. The subjects were randomly divided into two groups of 35 patients, one group treated with sucrose vaginal gel, and the other with metronidazole vaginal gel. The treatment period was 14 days for each group. At the end of the treatment period, the status of each woman's improvement was determined by elimination at least three out of four Amsel criteria (homogeneous vaginal discharge, presence of clue cells > 20%, positive whiff test and vaginal pH value > 4.5), and clinical complaints and reported side effects of medication were recorded for the patients. Data were analyzed using the t test, chi-squared test and McNemar's test).

RESULTS

The sucrose vaginal gel and metronidazole vaginal gel were not significantly different in reducing patients' clinical complaints or in elimination at least three out of four of the Amsel criteria that were positive before treatment. With an 85.7% improvement rate with sucrose gel and an 88.5% improvement rate with metronidazole gel, the differences in therapeutic response were not significant, and neither was statistically different in improving the disease (p = 0.389).

CONCLUSION

It seems that sucrose vaginal gel might be considered a possible alternative to metronidazole vaginal gel in the treatment of bacterial vaginosis.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials, IRCT2016112631105N1 . Registered on 27 December 2016.

Fish pathogen bacteria: Adhesion, parameters influencing virulence and interaction with host cells

Wild fisheries are declining due to over-fishing, climate change, pollution and marine habitat destructions among other factors, and, concomitantly, aquaculture is increasing significantly around the world. Fish infections caused by pathogenic bacteria are quite common in aquaculture, although their seriousness depends on the season. Drug-supplemented feeds are often used to keep farmed fish free from the diseases caused by such bacteria. However, given that bacteria can survive well in aquatic environments independently of their hosts, bacterial diseases have become major impediments to aquaculture development. On the other hand, the indiscriminate uses of antimicrobial agents has led to resistant strains and the need to switch to other antibiotics, although it seems that an integrated approach that considers not only the pathogen but also the host and the environment will be the most effective method in the long-term to improve aquatic animal health. This review covers the mechanisms of bacterial pathogenicity and details the foundations underlying the interactions occurring between pathogenic bacteria and the fish host in the aquatic environment, as well as the factors that influence virulence. Understanding and linking the different phenomena that occur from adhesion to colonization of the host will offer novel and useful means to help design suitable therapeutic strategies for disease prevention and treatment.

Mucus glycosylation, immunity and bacterial microbiota associated to the skin of experimentally ulcered gilthead seabream (Sparus aurata)

Interest in fish skin immunity and its associated microbiota has greatly increased among immunologists. The objective of this study is to know if skin ulcers may be associated with changes in the mucus composition and microbial diversity. The abundance of terminal carbohydrates, several enzymes (protease, antiprotease, peroxidase, lysozyme) and total immunoglobulin M levels were evaluated in skin mucus of experimentally ulcered gilthead seabream (Sparus aurata L.). Furthermore, the composition of the microbiota of ulcered and non-ulcered skin has been determined using Illumina Miseq technology. Significant decreases of terminal abundance of α-D-mannose, α-D-glucose and N-acetyl-galactosamine in skin mucus of ulcered fish, compared to control fish were detected. The levels of IgM and all the tested enzymes in mucus were decreased in ulcered fish (compared to control fish) although the observed decreases were only statistically significant for proteases and antiproteases. Concomitantly, the analysis of the composition of the skin microbiota showed clear differences between ulcered and non-ulcered areas. The genus taxonomic analysis showed that Staphylococcus and Lactobacillus were more abundant in non-ulcered skin whereas in ulcered area were Streptococcus and Granulicatella. Important decreases of the number of sequences related to Alteromonas, Thalassabius and Winogradskyella were detected in ulcered skin whilst slight increases of sequences related to Flavobacterium, Chryseobacterium and Tenacibaculum genera were observed. Overall these results demonstrated that the presence of skin ulcers provide microenvironments that perturb both the mucus composition and microbial biodiversity of this important external surface which seem to be more vulnerable to diseases.

AcfA is an essential regulator for pathogenesis of fish pathogen Vibrio alginolyticus

V. alginolyticus is an important opportunistic pathogen which causes vibriosis in aquatic animals. AcfA, as an accessory colonization factor, is hypothesized to be involved in the pathogenesis of infection. In this study, a mutant strain with an in-frame deletion removed nucleotides 86 to 561 of the acfA gene was constructed to reveal the role of AcfA in the physiology and virulence from V. alginolyticus. An acfA mutant showed a similar growth level, an obvious decrease in swarming motility and the activity of ECPase, a higher LD₅₀ value by intraperitoneal injection of grouper fish compared to that of the wild-type. Furthermore, the deletion of acfA could enhance the level of biofilm formation and suppress the polar flagellum forming. The comparative proteomic analysis demonstrated the deletion mutation of acfA could up-regulate the expression of 4 proteins of p4alcd, deoD, phb and DctP, and down-regulate the expression of 8 proteins of Clp, hpV36980, ABCtp, pepD, arA, aggp, fla and ompA compared to that of the wild-type. The analysis of RT-qPCR showed the mRNA levels of DctP and deoD were significantly induced, and the mRNA levels of pepD, arA, fla and ompA were significantly reduced in acfA mutant compared with the wild-type. The results suggest that acfA may contribute to the overall success in the pathogenesis of V. alginolyticus by regulating the expression of some relevant genes.

Role of the toxR Gene from Fish Pathogen Vibiro alginolyticus in the Physiology and Virulence

A mutant strain of Vibiro alginolyticus with an in-frame deletion of the toxR gene was constructed to reveal the role of ToxR in the physiology and virulence of V. alginolyticus. The statistical analysis showed no significant difference in the growth ability, swarming motility, activity of extracellular protease and the virulence by injection (the value of LD₅₀) between the wild-type and the toxR mutant. However, the deletion of toxR could decrease the level of biofilm formation. The comparative proteomic analysis demonstrated the deletion mutation of toxR could up-regulate the expression of glutamine synthetase and levansucrase, and down-regulate the expression of 10 proteins such as OmpU, DnaK, etc. These results suggest that ToxR may be involved in the early stages of infection by influencing colonization of the bacteria on the surface of the intestine through enhancing the biofilm information of V. alginolyticus via modulating the expression of glutamine synthetize, levansucrase and OmpU.

secA, secD, secF, yajC, and yidC contribute to the adhesion regulation of Vibrio alginolyticus

Vibrio alginolyticus caused great losses to aquaculture. Adhesion is an important virulence factor of V. alginolyticus. In this study, the relationship between V. alginolyticus adhesion and type II secretion system genes (secA, secD, secF, yajC, and yidC) was determined using gene silencing, qRT‐PCR and in vitro adhesion assay. The results showed that the expression of target genes and the bacterial adhesion exhibited significant decreases after transient gene silencing and stable gene silencing, which indicated that secA, secD, secF, yajC, and yidC played roles in the bacterial adhesion of V. alginolyticus. The expression of secA, secD, secF, yajC, and yidC were significantly influenced by temperature, salinity, pH and starvation. The results indicated that the expression of secA, secD, secF, yajC, and yidC were sensitive to different environmental factors, whereas environmental factors can affect V. alginolyticus adhesion via the expression of secA, secD, secF, yajC, and yidC.

Contributions of the oligopeptide permeases in multistep of Vibrio alginolyticus pathogenesis

Vibrio alginolyticus has been associated with several diseases of cultivated marine animals, and has led to considerable economic losses. The oligopeptide permease (Opp) has been proven to play a variety of important roles in nutrition and virulence in several bacteria. In our previous research, the opp gene cluster was identified in Vibrio alginolyticus with transcriptome sequence, which also indicated that the Opp system might play roles in the regulation of adhesion. In this study, the relationship between V. alginolyticus virulence and the opp gene cluster was determined using gene silencing followed by RT‐qPCR, in vitro adhesion assay, growth curves detection in the presence of glutathione (GSH) as a toxic substrate, hemolysis assay, biofilm assay, and artificial infection. Silencing these genes led to deficiencies in adhesion, peptide internalization, biofilm production, hemolytic activity, and virulence. The expression levels of hapr, hapa, tlh, and hlya, which are important genes closely related to the hemolytic activity of Vibrio, were significantly downregulated in all of the RNAi groups. Furthermore, the expression of oppA, oppB, oppC, oppD, and oppF was significantly influenced by temperature, starvation, and pH. These results indicate that (1) oppABCDF contributed in multistep of V. alginolyticus pathogenesis, including adhesion, biofilm production, and hemolytic activity; (2) oppABCDF was sensitive to different temperatures, changes in pH, and increased starvation time.

The complete genome sequence of Exiguobacterium arabatum W-01 reveals potential probiotic functions

Shrimp is extensively cultured worldwide. Shrimp farming is suffering from a variety of diseases. Probiotics are considered to be one of the effective methods to prevent and cure shrimp diseases. Exiguobacterium arabatum W‐01, a gram‐positive and orange‐pigmented bacterium, was isolated from the intestine of a healthy Penaeus vannamei specimen. Whole‐genome sequencing revealed a genome of 2,914,854 bp, with 48.02% GC content. In total, 3,083 open reading frames (ORFs) were identified, with an average length of 843.98 bp and a mean GC content of 48.11%, accounting for 89.27% of the genome. Among these ORFs, 2,884 (93.5%) genes were classified into Clusters of Orthologous Groups (COG) families comprising 21 functional categories, and 1,650 ORFs were classified into 83 functional Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. A total of 27 rRNA operons and 68 tRNAs were identified, with all 20 amino acids represented. In addition, 91 genomic islands, 68 potential prophages, and 33 tandem repeats, but no clustered regularly interspaced short palindromic repeats (CRISPRs), were found. No resistance genes and only one virulence gene were identified. Among the 150 secreted proteins of E. arabatum W‐01, a variety of transport system substrate‐binding proteins, enzymes, and biosynthetic proteins, which play important roles in the uptake and metabolism of nutrients, were found. Two adherence‐related protein genes and 31 flagellum‐related protein genes were also identified. Taken together, these results indicate potential probiotic functions for E. arabatum W‐01.

Effects of dietary supplementation with fenugreek seeds, alone or in combination with probiotics, on gilthead seabream (Sparus aurata L.) skin mucosal immunity

Despite increasing interest in modulating the immune response of fish, providing a combination of probiotics and herbal immunostimulants in aquafeed has rarely has been studied. The effects on gilthead seabream (Sparus aurata L.) of the dietary administration of fenugreek (Trigonella foenum graecum) seeds alone (FE), or combined with one of the following probiotic strains: Bacillus licheniformis (FEBL), Lactobacillus plantarum (FELP) or Bacillus subtilis (FEBS) were evaluated. Fish were fed a control or one of the supplemented diets for 3 weeks. After 2 and 3 weeks of the feeding trial, the abundance of terminal carbohydrates, IgM levels, enzymatic activities (proteases, alkaline phosphatase, esterase and ceruloplasmin) and bactericidal activity were determined in skin mucus. Our results demonstrated that the dietary administration of FE in combination with L. plantarum, particularly, increased carbohydrate abundance, the activity of certain enzymes such as ceruloplasmin, and bactericidal activity against the pathogenic bacterium Photobacterium damselae and the non-pathogenic bacterium B. subtilis in skin mucus at the end of the trial. The carbohydrates most affected by the FELP diet were mannose/glucose, N-acetyl-d-galactosamine and N-acetyl-β-d-glucosamine. Interestingly, IgM levels were significantly higher in fish fed the FELP and FEBS diets whilst protease activity generally increased in all supplemented diets, which could suggests that the main effect in this activity was to the result of FE supplementation although that fact cannot be confirmed because the effects of probiotics addition alone were not studied. These results suggest that the combined dietary administration of fenugreek and L. plantarum will best enhance the skin mucosal immunity response of gilthead seabream.

AcuC, a histone deacetylase, contributes to the pathogenicity of Aeromonas hydrophila

The interactions of pathogens and phagocytes are complex. Our study demonstrated that Aeromonas hydrophila B11 can survive in the macrophagocytes of Tilapia mossambica. To explore the regulatory processes of A. hydrophila survival in the macrophagocytes, we used the mini-Tn10 transposon mutagenesis system to build a mutant library by mixing Escherichia coli Sm10 (pLOFKm) and A. hydrophila B11. In total, 102 mutant colonies were detected, and 11 of them showed reduced survival in macrophagocytes. The mutant with the most severe phenotype, AM73, was chosen for further research. The ORF interrupted by mini-Tn10 in AM73 was approximately 960 bp and was deposited in GenBank with the accession number SRP049226. The 319 amino acid protein encoded by the ORF showed a high degree of identity (89%) with proteins in the histone deacetylase/AcuC/AphA family of A. hydrophila subsp. hydrophila ATCC7966. A strain (AC73) in which the acuC mutation was complemented was constructed by generating the recombinant expression plasmid pACYC184-acuC and introducing it into the AM73 mutant strain. Our experiments revealed that strain AM73 was deficient in biofilm formation, adhesion, survival in macrophagocytes, and virulence compared with A. hydrophila B11, and all of these biological properties were improved in strain AC73. The expression of 10 significant virulence genes was significantly inhibited in strain AM73. The results indicated that AcuC was an important regulatory protein contributing to the pathogenicity of A. hydrophila.

Transcriptome Analysis Reveals Comprehensive Insights into the Early Immune Response of Large Yellow Croaker (Larimichthys crocea) Induced by Trivalent Bacterial Vaccine

Vaccination is an effective and safe strategy for combating bacterial diseases in fish, but the mechanisms underlying the early immune response after vaccination remain to be elucidated. In the present study, we used RNA-seq technology to perform transcriptome analysis of spleens from large yellow croaker (Larimichthys crocea) induced by inactivated trivalent bacterial vaccine (Vibrio parahaemolyticus, Vibrio alginolyticus and Aeromonas hydrophila). A total of 2,789 or 1,511 differentially expressed genes (DEGs) were obtained at 24 or 72 h after vaccination, including 1,132 or 842 remarkably up-regulated genes and 1,657 or 669 remarkably down-regulated genes, respectively. Gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichments revealed that numerous DEGs belong to immune-relevant genes, involved in many immune-relevant pathways. Most of the strongly up-regulated DEGs are innate defense molecules, such as antimicrobial peptides, complement components, lectins, and transferrins. Trivalent bacterial vaccine affected the expressions of many components associated with bacterial ligand-depending Toll-like receptor signaling pathways and inflammasome formation, indicating that multiple innate immune processes were activated at the early period of vaccination in large yellow croaker. Moreover, the expression levels of genes involved in antigen processing were also up-regulated by bacterial vaccine. However, the expression levels of several T cell receptors and related CD molecules and signal transducers were down-regulated, suggesting that the T cell receptor signaling pathway was rapidly suppressed after vaccination. These results provide the comprehensive insights into the early immune response of large yellow croaker to vaccination and valuable information for developing a highly immunogenic vaccine against bacterial infection in teleosts.

Ribose operon repressor (RbsR) contributes to the adhesion of Aeromonas hydrophila to Anguilla japonica mucus

The characterization of adhesion between pathogenic bacteria and the host is critical. Pathogenic Aeromonas hydrophila was shown to adhere in vitro to the mucus of Anguilla japonica. To further investigate the adhesion mechanisms of A. hydrophila, a mini-Tn10 transposon mutagenesis system was used to generate an insertion mutant library by cell conjugation. Seven mutants that were impaired in adhesion to mucus were selected out of 332 individual colonies, and mutant M196 was the most severely impaired strain. National Center for Biotechnology Information (NCBI) blast analysis showed that mutant M196 was inserted by mini-Tn10 with an ORF of approximately 1,005 bp (GenBank accession numbers KP280172). This ORF is predicted to encode a protein consist of 334 amino acid, which displays the highest identity (98%) with the RbsR of A. hydrophila ATCC 7966. Random inactivation of rbsR gene affected the pleiotropic phenotypes of A. hydrophila. The adhesion ability and the survival level of the rbsR gene mutant (M196) were attenuated compared with the wild-type and rbsR complementary type. The findings of this study indicated that RbsR plays roles in the bacterial adhesion and intracellular survival of A. hydrophila.

Enhancing gilthead seabream immune status and protection against bacterial challenge by means of antigens derived from Vibrio parahaemolyticus

In an attempt to control the proliferation of the pathogenic bacterium Vibrio parahaemolyticus in gilthead seabream (Sparus aurata), the immunostimulant effect of lysate and ToxA from this bacterium was evaluated. Fish were intraperitoneally injected twice (first injection, day 1 of the experiment; second injection, day 7) and sampled after one week (on days 8 and 15). Afterwards, all fish specimens were experimentally infected with V. parahaemolyticus and mortality was recovered for 1 week. Fish injected with lysate, ToxA and phosphate buffer saline (control) showed 100%, 50% and 0% survival, respectively, when challenged with the pathogen. Skin mucus immune parameters and immune-related gene expression in skin and spleen were also evaluated. The results showed that mucus immune parameters were enhanced in the lysate and ToxA groups compared with the values obtained for fish from the control group. Expression of IL-1β, TNF-α, C3 and IgM genes was significantly up-regulated in the lysate and ToxA groups, principally after infection with the bacterium. Interestingly, TLR5 gene expression increased in fish immunized with lysate. The most prominent histological characteristic in gut from infected fish was the presence of a great number of intraepithelial leucocytes as well as inflammation of the submucosa, while severe hydropic degeneration and hemosiderosis were detected in liver from infected fish. Injection of lysate or ToxA had a protective effect against the deleterious consequences of subsequent infection with V. parahaemolyticus in gut and liver. The findings underline the potential of lysate and ToxA as potent preventive antigens against this kind of vibriosis.

flrA, flrB and flrC regulate adhesion by controlling the expression of critical virulence genes in Vibrio alginolyticus

Adhesion is an important virulence trait of Vibrio alginolyticus. Bacterial adhesion is influenced by environmental conditions; however, the molecular mechanism underlying this effect remains unknown. The expression levels of flrA, flrB and flrC were significantly downregulated in adhesion-deficient V. alginolyticus strains cultured under Cu²⁺, Pb²⁺, Hg²⁺ and low-pH stresses. Silencing these genes led to deficiencies in adhesion, motility, flagellar assembly, biofilm formation and exopolysaccharide (EPS) production. The expression levels of fliA, flgH, fliS, fliD, cheR, cheV and V12G01_22158 (Gene ID) were significantly downregulated in all of the RNAi groups, whereas the expression levels of toxT, ctxB, acfA, hlyA and tlh were upregulated in flrA- and flrC-silenced groups. These genes play a key role in the virulence mechanisms of most pathogenic Vibrio species. Furthermore, the expression of flrA, flrB and flrC was significantly influenced by temperature, salinity, starvation and pH. These results indicate that (1) flrA, flrB and flrC are important for V. alginolyticus adhesion; (2) flrA, flrB and flrC significantly influence bacterial adhesion, motility, biofilm formation and EPS production by controlling expression of key genes involved in those phenotypes; and (3) flrA, flrB and flrC regulate adhesion in the natural environment with different temperatures, pH levels, salinities and starvation time.

Genome-Wide Detection of Predicted Non-coding RNAs Related to the Adhesion Process in Vibrio alginolyticus Using High-Throughput Sequencing

The ability of bacteria to adhere to fish mucus can be affected by environmental conditions and is considered to be a key virulence factor of Vibrio alginolyticus. However, the molecular mechanism underlying this ability remains unclear. Our previous study showed that stress conditions such as exposure to Cu, Pb, Hg, and low pH are capable of reducing the adhesion ability of V. alginolyticus. Non-coding RNAs (ncRNAs) play a crucial role in the intricate regulation of bacterial gene expression, thereby affecting bacterial pathogenicity. Thus, we hypothesized that ncRNAs play a key role in the V. alginolyticus adhesion process. To validate this, we combined high-throughput sequencing with computational techniques to detect ncRNA dynamics in samples after stress treatments. The expression of randomly selected novel ncRNAs was confirmed by QPCR. Among the significantly altered ncRNAs, 30 were up-regulated and 2 down-regulated by all stress treatments. The QPCR results reinforced the reliability of the sequencing data. Target prediction and KEGG pathway analysis indicated that these ncRNAs are closely related to pathways associated with in vitro adhesion, and our results indicated that chemical stress-induced reductions in the adhesion ability of V. alginolyticus might be due to the perturbation of ncRNA expression. Our findings provide important information for further functional characterization of ncRNAs during the adhesion process of V. alginolyticus.

Virgibacillus proomii and Bacillus mojavensis as probiotics in sea bass (Dicentrarchus labrax) larvae: effects on growth performance and digestive enzyme activities

This study examined the effects of two probiotics (Virgibacillus proomii and Bacillus mojavensis) on the digestive enzyme activity, survival and growth of Dicentrarchus labrax at various ontogenetic stages in three separate experiments. These probiotics were incorporated as single or mixed into fish feed for a period of 60 days. The growth parameters, proximate composition of whole body, digestive enzymes and gut microbiology were monitored at regular. The increments in length and weight and the survival were significantly higher (P < 0.05), and the values of food conversions were significantly lower (P < 0.05) in fishes fed the probiotic. The administration of V. proomii and B. mojavensis in diet resulted in an increase (P > 0.05) in body ash and protein content and in the specific activity of phosphatase alkaline and amylase in the digestive tract of all the fishes. V. proomii and B. mojavensis persisted in the fish intestine and in the feed in high numbers during the feeding period (group 1: 5.8 × 10(4) CFU/ml, group 2: 9.6 × 10(4) CFU/ml, and group 3: 9.8 × 10(4) CFU/ml day 60). The two probiotics V. proomii and B. mojavensis were adequate for improved growth performance and survival and for healthy gut microenvironment of the host.

Enrichment of gilthead seabream (Sparus aurata L.) diet with palm fruit extracts and probiotics: Effects on skin mucosal immunity

Fish skin mucus contains numerous immune substances still poorly studied. To date, there are no studies regarding the possible influence of dietary supplements on such important substances. In the present work, a commercial diet used as control diet was enriched with: 1) probiotic Shewanella putrefaciens (Pdp11 diet, 10(9) cfu g(-1)); 2) probiotic Bacillus sp. (Bacillus diet, 10(9) ufc g(-1)); 3) aqueous date palm fruits extracts (DPE diet, 4%), and 4) a combination of Pdp11 + Bacillus sp + aqueous DPE (Mix diet). After 2 and 4 weeks of the feeding trial, enzymatic activities (proteases, antiproteases and peroxidases), IgM levels and terminal carbohydrates abundance were determined in skin mucus. In addition, the expression of certain immune related genes was evaluated in the skin. Our results demonstrated the significant alteration of the terminal carbohydrate abundance in skin mucus. Carbohydrates more affected by experimental diets were N-acetyl-galactosamine, N-acetyl-glucosamine, galactose, mannose, glucose and fucose. IgM, peroxidase activity and protease were also significantly higher in fish fed enriched diets. For last, an important up-regulation on the immune related gene studied on the skin was also detected. Present findings provide robust evidence that fish skin mucosal immunity can be improved by the diet.

Involvement of the flagellar assembly pathway in Vibrio alginolyticus adhesion under environmental stresses

Adhesion is an important virulence factor of Vibrio alginolyticus. This factor may be affected by environmental conditions; however, its molecular mechanism remains unclear. In our previous research, adhesion deficient strains were obtained by culturing V. alginolyticus under stresses including Cu, Pb, Hg, and low pH. With RNA-seq and bioinformatics analysis, we found that all of these stress treatments significantly affected the flagellar assembly pathway, which may play an important role in V. alginolyticus adhesion. Therefore, we hypothesized that the environmental stresses of the flagellar assembly pathway may be one way in which environmental conditions affect adhesion. To verify our hypothesis, a bioinformatics analysis, QPCR, RNAi, in vitro adhesion assay and motility assay were performed. Our results indicated that (1) the flagellar assembly pathway was sensitive to environmental stresses, (2) the flagellar assembly pathway played an important role in V. alginolyticus adhesion, and (3) motility is not the only way in which the flagellar assembly pathway affects adhesion.

Identification and characterization of three Vibrio alginolyticus non-coding RNAs involved in adhesion, chemotaxis, and motility processes

The capability of Vibrio alginolyticus to adhere to fish mucus is a key virulence factor of the bacteria. Our previous research showed that stress conditions, such as Cu(2+), Pb(2+), Hg(2+), and low pH, can reduce this adhesion ability. Non-coding (nc) RNAs play a crucial role in regulating bacterial gene expression, affecting the bacteria's pathogenicity. To investigate the mechanism(s) underlying the decline in adhesion ability caused by stressors, we combined high-throughput sequencing with computational techniques to detect stressed ncRNA dynamics. These approaches yielded three commonly altered ncRNAs that are predicted to regulate the bacterial chemotaxis pathway, which plays a key role in the adhesion process of bacteria. We hypothesized they play a key role in the adhesion process of V. alginolyticus. In this study, we validated the effects of these three ncRNAs on their predicted target genes and their role in the V. alginolyticus adhesion process with RNA interference (i), quantitative real-time polymerase chain reaction (qPCR), northern blot, capillary assay, and in vitro adhesion assays. The expression of these ncRNAs and their predicted target genes were confirmed by qPCR and northern blot, which reinforced the reliability of the sequencing data and the target prediction. Overexpression of these ncRNAs was capable of reducing the chemotactic and adhesion ability of V. alginolyticus, and the expression levels of their target genes were also significantly reduced. Our results indicated that these three ncRNAs: (1) are able to regulate the bacterial chemotaxis pathway, and (2) play a key role in the adhesion process of V. alginolyticus.

Investigation of possible molecular mechanisms underlying the regulation of adhesion in Vibrio alginolyticus with comparative transcriptome analysis

Adhesion capability to fish mucus, which can be affected by environmental conditions, is considered to be a key virulence factor of Vibrio alginolyticus although the molecular mechanism is still unclear. In the present study, V. alginolyticus was treated with stress conditions including Cu(2+) (50 mg/L), Pb(2+) (100 mg/L), Hg(2+) (50 mg/L) and low pH (pH 5). We found these stress treatments were capable of reducing the adhesion of V. alginolyticus, while the expression levels of multiple genes were significantly changed according to the results of high throughput sequencing. The expression of randomly selected genes was confirmed by QPCR, which reinforced the reliability of the sequencing data. Ontology assignments and KEGG pathway analysis indicated that stress treatments affect pathways that may be related to adhesion. Our results identified genes which might play a key role in the adhesion process of V. alginolyticus, which could lay a foundation for further functional analysis of these genes in the process of adhesion. As these genes were sensitive to environmental factors, this may explain why the adhesion process can be influenced by environmental factors.

Probiotic supplementation influences the diversity of the intestinal microbiota during early stages of farmed senegalese sole (Solea Senegalensis, Kaup 1858)

Ingestion of bacteria at early stages results in establishment of a primary intestinal microbiota which likely undergoes several stages along fish life. The role of this intestinal microbiota regulating body functions is crucial for larval development. Probiotics have been proved to modulate this microbiota and exert antagonistic effects against fish pathogens. In the present study, we aimed to determine bacterial diversity along different developmental stages of farmed Senegalese sole (Solea senegalensis) after feeding probiotic (Shewanella putrefaciens Pdp11) supplemented diet for a short period (10-30 days after hatching, DAH). Intestinal lumen contents of sole larvae fed control and probiotic diets were collected at 23, 56, 87, and 119 DAH and DNA was amplified using 16S rDNA bacterial domain-specific primers. Amplicons obtained were separated by denaturing gradient gel electrophoresis (DGGE), cloned, and resulting sequences compared to sequences in GenBank. Results suggest that Shewanella putrefaciens Pdp11 induces a modulation of the dominant bacterial taxa of the intestinal microbiota from 23 DAH. DGGE patterns of larvae fed the probiotic diet showed a core of bands related to Lactobacillus helveticus, Pseudomonas acephalitica, Vibrio parahaemolyticus, and Shewanella genus, together with increased Vibrio genus presence. In addition, decreased number of clones related to Photobacterium damselae subsp piscicida at 23 and 56 DAH was observed in probiotic-fed larvae. A band corresponding to Shewanella putrefaciens Pdp11 was sequenced as predominant from 23 to 119 DAH samples, confirming the colonization by the probiotics. Microbiota modulation obtained via probiotics addition emerges as an effective tool to improve Solea senegalensis larviculture.

Notable mucosal immune responses induced in the intestine of zebrafish (Danio rerio) bath-vaccinated with a live attenuated Vibrio anguillarum vaccine

Live attenuated vaccine is one of the efficient vaccine candidates in aquaculture, which can be easily delivered to fish via bath-vaccination. An outstanding advantage of bath-vaccination is that vaccine delivery is through the same route as that utilized by many fish pathogens, generating specific mucosal immune responses. In this work, we investigated the mucosal immune responses induced by a live attenuated Vibrio anguillarum vaccine in zebrafish via bath-vaccination. Bacteria proliferated rapidly in 3 h after vaccination and maintained at a high level until 6 h in the intestine. Besides, bacteria persisted in the intestine for a longer time whereas decreased rapidly in the skin and gills. Moreover, a significant up-regulation of TLR5 triggering a MyD88-dependent signaling pathway was observed in the intestine, which implied that flagella were the crucial antigenic component of the live attenuated vaccine. And macrophages and neutrophils showed active responses participating in antigen recognition and sampling after vaccination. Furthermore, an inflammation was observed with plenty of lymphocytes in the intestine at 24 h post vaccination but eliminated within 7 days. In conclusion, the live attenuated V. anguillarum vaccine induced notable mucosal immune responses in the intestine which could be used as a mucosal vaccine vector in the future.