Vibrio harveyi: a significant pathogen of marine vertebrates and invertebrates

Designing a novel mRNA vaccine against Vibrio harveyi infection in fish: an immunoinformatics approach

Vibrio harveyi belongs to the family Vibrionaceae of class Gammaproteobacteria. Around 12 Vibrio species can cause gastroenteritis (gastrointestinal illness) in humans. A large number of bacterial particles can be found in the infected cells, which may cause death. Despite these devastating complications, there is still no cure or vaccine for the bacteria. As a result, we used an immunoinformatics approach to develop a multi-epitope vaccine against the most pathogenic hemolysin gene of V. harveyi. The immunodominant T- and B-cell epitopes were identified using the hemolysin protein. We developed a vaccine employing three possible epitopes: cytotoxic T-lymphocytes, helper T-lymphocytes, and linear B-lymphocyte epitopes, after thorough testing. The vaccine was developed to be antigenic, immunogenic, and non-allergenic, as well as have a better solubility. Molecular dynamics simulation revealed significant structural stiffness and binding stability. In addition, the immunological simulation generated by computers revealed that the vaccination might elicit immune reactions Escherichia coli K12 as a model, codon optimization yielded ideal GC content and a higher codon adaptation index value, which was then included in the cloning vector pET2+ (a). Altogether, our experiment implies that the proposed peptide vaccine might be a good option for vibriosis prophylaxis.

Quorum Quenching Strains Isolated from the Microbiota of Sea Anemones and Holothurians Attenuate Vibriocorallilyticus Virulence Factors and Reduce Mortality in Artemiasalina

Interference with quorum-sensing (QS) intercellular communication systems by the enzymatic disruption of N-acylhomoserine lactones (AHLs) in Gram-negative bacteria has become a promising strategy to fight bacterial infections. In this study, seven strains previously isolated from marine invertebrates and selected for their ability to degrade C6 and C10-HSL, were identified as Acinetobacter junii, Ruegeria atlantica, Microbulbifer echini, Reinheimera aquimaris, and Pseudomonas sihuiensis. AHL-degrading activity against a wide range of synthetic AHLs were identified by using an agar well diffusion assay and Agrobacterium tumefaciens NTL4 and Chromobacterium violaceum CV026 and VIR07 as biosensors. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis indicated that this activity was not due to an AHL lactonase. All the strains degraded Vibrio coralliilyticus AHLs in coculture experiments, while some strains reduced or abolished the production of virulence factors. In vivo assays showed that strains M3-111 and M3-127 reduced this pathogen’s virulence and increased the survival rate of Artemia salina up to 3-fold, indicating its potential use for biotechnological purposes. To our knowledge, this is the first study to describe AHL-degrading activities in some of these marine species. These findings highlight that the microbiota associated with marine invertebrates constitute an important underexplored source of biological valuable compounds.

Eukaryotic catecholamine hormones influence the chemotactic control of Vibrio campbellii by binding to the coupling protein CheW

Host-emitted stress hormones significantly influence the growth and behavior of various bacterial species; however, their cellular targets have so far remained elusive. Here, we used customized probes and quantitative proteomics to identify the target of epinephrine and the α-adrenoceptor agonist phenylephrine in live cells of the aquatic pathogen Vibrio campbellii. Consequently, we have discovered the coupling protein CheW, which is in the center of the chemotaxis signaling network, as a target of both molecules. We not only demonstrate direct ligand binding to CheW but also elucidate how this affects chemotactic control. These findings are pivotal for further research on hormone-specific effects on bacterial behavior.

In addition to their well-known role as stress-associated catecholamine hormones in animals and humans, epinephrine (EPI) and norepinephrine (NE) act as interkingdom signals between eukaryotic hosts and bacteria. However, the molecular basis of their effects on bacteria is not well understood. In initial phenotypic studies utilizing Vibrio campbellii as a model organism, we characterized the bipartite mode of action of catecholamines, which consists of promotion of growth under iron limitation and enhanced colony expansion on soft agar. In order to identify the molecular targets of the hormones, we designed and synthesized tailored probes for chemical proteomic studies. As the catechol group in EPI and NE acts as an iron chelator and is prone to form a reactive quinone moiety, we devised a photoprobe based on the adrenergic agonist phenylephrine (PE), which solely influenced colony expansion. Using this probe, we identified CheW, located at the core of the chemotaxis signaling network, as a major target. In vitro studies confirmed that EPI, NE, PE, and labetalol, a clinically applied antagonist, bind to purified CheW with affinity constants in the submicromolar range. In line with these findings, exposure of V. campbellii to these adrenergic agonists affects the chemotactic control of the bacterium. This study highlights an effect of eukaryotic signaling molecules on bacterial motility.

The microbiome: A heritable contributor to bone morphology?

Bone provides structure to the vertebrate body that allows for movement and mechanical stimuli that enable and the proper development of neighboring organs. Bone morphology and density is also highly heritable. In humans, heritability of bone mineral density has been estimated to be 50-80%. However, genome wide association studies have so far explained only 25% of the variation in bone mineral density, suggesting that a substantial portion of the heritability of bone mineral density may be due to environmental factors. Here we explore the idea that the gut microbiome is a heritable environmental factor that contributes to bone morphology and density. The vertebrae skeleton has evolved over the past ~500 million years in the presence of commensal microbial communities. The composition of the commensal microbial communities has co-evolved with the hosts resulting in species-specific microbial populations associated with vertebrate phylogeny. Furthermore, a substantial portion of the gut microbiome is acquired through familial transfer. Recent studies suggest that the gut microbiome also influences postnatal development. Here we review studies from the past decade in mice that have shown that the presence of the gut microbiome can influence postnatal bone growth regulating bone morphology and density. These studies indicate that the presence of the gut microbiome may increase longitudinal bone growth and appositional bone growth, resulting differences cortical bone morphology in long bones. More surprising, however are recent studies showing that transfer of the gut microbiota among inbred mouse strains with distinct bone phenotypes can alter postnatal development and adult bone morphology. Together these studies support the concept that the gut microbiome is a contributor to skeletal phenotype.

The increased prevalence of Vibrio species and the first reporting of Vibrio jasicida and Vibrio rotiferianus at UK shellfish sites

Warming sea-surface temperature has led to an increase in the prevalence of Vibrio species in marine environments. This can be observed particularly in temperate regions where conditions for their growth has become more favourable. The increased prevalence of pathogenic Vibrio species has resulted in a worldwide surge of Vibriosis infections in human and aquatic animals. This study uses sea-surface temperature data around the English and Welsh coastlines to identify locations where conditions for the presence and growth of Vibrio species is favourable. Shellfish samples collected from three locations that were experiencing an increase in sea-surface temperature were found to be positive for the presence of Vibrio species. We identified important aquaculture pathogens Vibrio rotiferianus and Vibrio jasicida from these sites that have not been reported in UK waters. We also isolated human pathogenic Vibrio species including V. parahaemolyticus from these sites. This paper reports the first isolation of V. rotiferianus and V. jasicida from UK shellfish and highlights a growing diversity of Vibrio species inhabiting British waters.

Antibiotics, antibiotic resistance genes and microbial community in grouper mariculture

Increasing use of feed and medicine in mariculture could cause negative environmental impacts such as habitat modification, microbial disease development and antibiotic resistance. Here we investigated contamination of antibiotics and antibiotic resistance genes (ARGs), and composition of microbial community in grouper mariculture systems in Hainan province, China. Results showed detection of various antibiotic residues with the dominance of fluoroquinolones and tetracyclines in the six grouper cultivation systems. The concentrations of the detected antibiotics in the grouper mariculture water were significantly higher than those in the original seawater. Some of the detected antibiotics such as enrofloxacin, ciprofloxacin, ofloxacin, oxytetracycline and erythromycin in the mariculture water and/or sediment would pose high resistance selection risks. Sulfonamides resistance genes sul1 and sul2 were found to be predominant in water and sediment, while tetracycline resistance genes were prevalent in fish gill and gut. The dominant bacterial phyla in water and sediments were Bacteroides, Actinomycetes, and Proteobacteria, while the dominant ones in fish gill and gut were the Proteobacteria. Genera of Vibrio and Mycobacterium in the core microbiota were important zoonotic pathogens, and there was a significant positive correlation between Vibrio and ARGs. Phyla of Proteobacteria, Actinomyces, and Cyanobacteria were positively correlated to ARGs, indicating that these microorganisms are potential hosts of ARGs. The putative functions of microbiome related to antibiotic resistance and human diseases were significantly higher in fish than in the mariculture environment. This study suggests that mariculture system is a reservoir of ARGs, and the use of antibiotics in mariculture could induce the increase of antibiotic resistance and the prevalence of opportunistic pathogens.

Pine (Pinus massoniana Lamb.) Needle Extract Supplementation Improves Performance, Egg Quality, Serum Parameters, and the Gut Microbiome in Laying Hens

The effects of Masson pine (Pinus massoniana Lamb.) needle extract (PNE) on gastrointestinal disorders and oxidative stress have been widely investigated using experimental models; however, the functions and mechanisms of these effects in chicken models remain unknown. We investigated the effects of Masson PNE supplementation on performance, egg quality, serum parameters, and the gut microbiome in laying hens. A total of 60 healthy 50-week-old Peking Pink laying hens with similar body conditions and egg production were randomly divided into the control (CON) (0 mg/kg PNE), PNE100 (100 mg/kg PNE), PNE200 (200 mg/kg PNE), and PNE400 (400 mg/kg PNE) groups, with fifteen replicates per treatment and one hen per replicate. Compared with the CON group, egg mass, feed conversion ratios, and yolk weight were significantly increased (p < 0.01) in the PNE100 group. Dietary supplementation of 100 mg/kg PNE increased the serum total protein, albumin, and glucose concentrations (p < 0.01) and decreased the alanine aminotransferase activity (p < 0.05) compared with those of the CONs. Hens in the PNE100 group had reduced serum malondialdehyde levels (p < 0.05) and increased catalase, superoxide dismutase, and glutathione peroxidase activities (p < 0.01) compared with those of the CON group. Serum proinflammatory cytokine concentrations of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α were lower (p < 0.01) and the IL-10 level was higher (p < 0.01) in the PNE100 group than in the CON group. Serum immunoglobulin (Ig)A, IgG, and IgM concentrations were increased in the PNE100 group (p < 0.01). The relative abundance of Bacteroidetes was increased, while the relative abundances of Firmicutes and Proteobacteria were decreased in the PNE100 group. The relative abundances of Vibrio, Shewanella, and Lactobacillus were decreased, while the relative abundances of unclassified_o_Bacteroidales, Rikenellaceae_RC9_gut_group, unclassified_f_Rikenellaceae, and Butyricicoccaceae were increased in the PNE100 group compared with those of the CON group. PNE supplementation at 100 mg/kg improved the diversity and structure of the gut microbial composition, production performance, egg quality, and serum parameters of laying hens. The laying hens in this study had good production performance when supplemented with 100 mg/kg PNE.

Antibiogram signatures of Vibrio species recovered from surface waters in South Western districts of Uganda: Implications for environmental pollution and infection control

Reports of vibriosis and other related gastrointestinal infections have remained a recurring concern in the diverse global continent. The safety of drinking surface water and associated environmental pollution has remained a public health concern in limited resource sittings. Seen in this light, we report the antibiogram signatures of Vibrio species recovered from surface waters in the South-Western districts of Uganda. Surface water samples were collected for four months for Vibrio species isolation in four districts (Bushenyi-B, Mitooma-M, Rubirizi-R, and Sheema-S) using bacteria culture procedures, disc diffusion and Polymerase Chain Reaction (PCR) technique. Isolates were characterised, and the antibiotic fingerprints were determined using PCR and nine selected antibiotics in routine use. A total of 392 Vibrio species were confirmed from the various districts (B: 172, M: 79. R: 60, S: 81), with 163 (94.77%) resistant to colistin (polymixin), 145 (84.3%) resistant to cefotaxime, 127 (73.84%) resistant to azithromycin, and 33 (19.19%) resistant to chloramphenicol among Bushenyi isolates. A similar high resistance to fluoroquinolones and carbapenem antibiotics were also recorded in other districts of the study area. A complete multiple antibiotic resistance phenotype ((M)ARPs) to the applied antibiotics (A-CTX-CXM-MEM-ATH-K-TM-C-PB-NI-CIP-NA) were also recorded among some isolates, which produced multiple antibiotic resistance indexes of 1, suggesting a high-risk source of contamination due to the usage of several antibiotics. The PCR reports also confirm ampC gene {20 (10.9%)}, beta-lactamase TEM gene (blaTEM2), {30 (10%)} and dihydropteroate synthase type-1 and 11 gene (sul 1 & 11) {16 (8%)}. The results present an implicated environmental pollution problem and a potential concern to public health, therefore there is the need for control of such infectious bacteria and environmental pollution monitoring. Hence, it is recommended various approaches crucial to monitoring of emerging trends in drug resistance at the local and international levels.

Evaluation of the Antimicrobial Effect of Graphene Oxide Fiber on Fish Bacteria for Application in Aquaculture Systems

The growing importance of the domestic aquaculture industry has led not only to its continuous development and expansion but also to an increase in the production of wastewater containing pathogenic microorganisms and antibiotic-resistant bacteria. As the existing water purification facilities have a high initial cost of construction, operation, and maintenance, it is necessary to develop an economical solution. Graphene oxide (GO) is a carbon-based nanomaterial that is easy to manufacture, inexpensive and has excellent antimicrobial properties. In this study, the antimicrobial effect of GO polyester fibers on seven species of fish pathogenic bacteria was analyzed to evaluate their effectiveness in water treatment systems and related products. As a result of incubating GO polyester fibers with seven types of fish pathogenic bacteria for 1, 6, and 12 h, there was no antimicrobial effect in Vibrio harveyi, V. scopthalmi, and Edwardsiella tarda. In contrast, GO fibers showed antimicrobial effects of more than 99% against A. hydrophila, S. parauberis, S. iniae, and P. piscicola, suggesting the potential use of GO fibers in water treatment systems.

Alginate poly and oligosaccharide (AOS) from Sargassum sp. as immunostimulant in gnotobiotic artemia challenge tests and antibacterial diffusion disc assay against pathogenic Vibrio parahaemolyticus, V. vulnificus and V. harveyi

Alginate is a polysaccharide derived from Sargassum sp. and is a potent immunostimulant with antibacterial activity, including against Vibrio spp. This genus of bacteria is found in freshwater and marine environments and is a common infectious, pathogenic bacteria both for aquatic cultivans and humans. Here, we determined the ability of sodium alginate polysaccharides and oligosaccharides (AOS) to act as immunostimulants in Artemia challenge tests and antibacterial diffusion disc assays against Vibrio parahaemolyticus, V. vulnificus, and V. harveyi. The AOS was produced by thermal heating. Dry sodium alginates were weighed out from 4.21 to 6.47 grams with a yield varying from 21.05 to 32.35%. Alginate polysaccharides were challenged against V harveyi and showed 8 positive results. The highest inhibitor zone was 12.962±3.623 mm. Based on 18 tests, AOS showed 12 positive results, with the highest inhibitor zone being 10.250±0.09 mm. The encapsulated alginate against Vibrio parahaemolyticus, Vibrio harveyi, Vibrio vulnificus, and the non-challenged tests without any Vibrio spp. addition resulted in the best concentrations of 800 ppm (polysaccharide) and 600 ppm (oligosaccharide), respectively. The lower concentration of oligosaccharides alginate were more effective and has the potential to be superior as an antibacterial agent and immunestimulant, as opposed to alginate polysaccharide.

Myrobalan-Mediated Nanocolloids in Controlling Marine Pathogens

Aquaculture production is affected by disease outbreak, which affects the production, profitability, and sustainability of the global aquaculture industry. Antibiotics have been widely used to control various infectious diseases. Indiscriminate usage of antibiotics results in development of antibiotic resistance in pathogens. This current study aims to synthesize myrobalan-mediated green silver nanocolloids (MBNc) by using the extract of three myrobalans and characterized by using various physiochemical techniques. Antibacterial potential of MBNc was screened in vibriosis causing pathogens (V. harveyi, V. alginolyticus, V. Parahaemolyticus), and foodborne pathogen S. haemolyticus, isolated from infected fish. Further, the presence of ESBL genes including CTX-M-15 and Amp C was analyzed in control and MBNc-treated strains. From our studies, it was observed that MBNc was very effective in controlling the growth. MBNc confirmed the anti-biofilm property in all tested marine pathogens and effectively abolish the genes encoding CTX-M-15 in tested pathogens. Thus, MBNc can be formulated to control the growth of marine pathogens and it can be used as an alternative to antibiotics to prevent infection in cage culturing and aquafarming.

LuxS modulates motility and secretion of extracellular protease in fish pathogen Vibrio harveyi

In this study, an in-frame deletion of the luxS gene was constructed to reveal the role of LuxS in the physiology and virulence of V. harveyi. The statistical analysis showed no significant differences in the growth ability, biofilm formation, antibiotic susceptibility, virulence by intraperitoneal injection, and the ability of V. harveyi to colonize the spleen and liver of the pearl gentian grouper between the wild-type (WT) and the luxS mutant. However, the deletion of luxS decreased the secretion of extracellular protease, while increased the ability of swimming and swarming. Simultaneously, a luxS-deleted mutant showed overproduction of lateral flagella, and an intact luxS complemented the defect. Since motility is flagella dependent, 16 of V. harveyi flagella biogenesis related genes were selected for further analysis. Based on quantitative real-time reverse transcription-PCR (qRT-PCR), the expression levels of these genes, including the polar flagella genes flaB, flhA, flhF, flhB, flhF, fliS, and flrA and the lateral flagella genes flgA, flgB, fliE, fliF, lafA, lafK, and motY, were significantly up-regulated in the ΔluxS: pMMB207 (ΔluxS+) strain as compared with the V. harveyi 345: pMMB207 (WT+) and C-ΔluxS strains during the early, mid-exponential, and stationary growth phase.

PCR, in-situ hybridization, and phylogenetic analysis suggest that 'big belly' disease in barramundi, Lates calcarifer (Bloch), is caused by a novel Vibrio species

'Big belly' disease is a chronic, granulomatous bacterial enteritis and peritonitis, first reported in 3- to 4-week-old Asian seabass or barramundi, Lates calcarifer Bloch fry. Affected fry are emaciated and have a swollen abdomen, and the condition is referred to as 'skinny pot-belly' or 'big belly' disease. In this study, histopathological examinations of diseased fish from a batch of 2-month-old, 6- to 8-cm L. calcarifer fingerlings, kept in seawater recirculating aquaculture systems, showed pathology resembling 'big belly' disease. Ethanol-fixed tissues were tested positive using specific PCR primers based on 16S rRNA genes. In situ hybridization using dioxygenin-labelled positive PCR products on formalin-fixed paraffin-embedded tissues showed positive reactions with intralesional, clusters of the large, 'big belly' coccobacilli. A phylogenetic tree constructed based on analyses of these 16S rRNA gene PCR products from five positive fish suggests that the 'big belly' bacterium is most likely a novel Vibrio species.

Pathogen of Vibrio harveyi infection and C-type lectin proteins in whiteleg shrimp (Litopenaeus vannamei)

Diseases caused by Vibrio harveyi in shrimps have gradually become one group of the most serious threats to shrimp production, while related molecular mechanisms of infections with Vibrio harveyi are still not known well in shrimps. Here, we performed proteomic sequencing of hepatopancreas in whiteleg shrimps (Litopenaeus vannamei) infected with exogenous Vibrio harveyi, and subsequent functional annotation and calculation of differentially expressed proteins (DEPs) in this study. A total of 145 DEPs were obtained, among them 36 were up-regulated and 109 were down-regulated after the infection. Meanwhile, our results showed that after the infection of Vibrio harveyi, expression levels of a variety of C-type lectins (CTLs) were changed significantly. In-depth functional domain analysis and spatial structure prediction of these CTLs revealed that amino acid sequences and spatial structures of the C-type lectin domain (CTLD) shared by the CTL-S and IML proteins were variant, suggesting differential functions between the two CTLs. In summary, various members of the CTL family have different epidemic responses to Vibrio harveyi infection, which provides a theoretical guidance for deep-going investigations on practical immunity reactions and pathogen infections in shrimps.

ToxR modulates biofilm formation in fish pathogen Vibrio harveyi

Vibrio harveyi is a common aquaculture pathogen causing diseases in a variety of aquatic animals. toxR, a conserved virulence-associated gene in vibrios, is identified in V. harveyi 345, a pathogenic strain isolated from diseased fish. In this study, to gain insight into function of ToxR in V. harveyi, an in-frame deletion of the toxR gene was constructed to reveal the role of ToxR in the physiology and virulence of V. harveyi. The statistical analysis showed no significant differences in the growth ability, motility, extracellular protease secretion, antibiotic susceptibility, virulence by intraperitoneal injection and the ability of V. harveyi to colonize the spleen and liver tissues of the pearl gentian grouper between the wild-type (WT) and the toxR mutant. However, the deletion of toxR increased the biofilm formation. The structure of the V. harveyi biofilm was further analysed by using scanning electron microscopy (SEM) and confocal laser scanning microscopy, and the results showed that deletion of toxR increased the number and density of V. harveyi biofilm. Since biofilm production is flagella, exopolysaccharide (EPS) and lipopolysaccharide dependent, 16 of V. harveyi biofilm-related genes were selected for further analysis. Based on quantitative real-time reverse transcription-PCR, the expression levels of these genes, including genes flrB, motY and mshA, flaE, flrA and gmhD, were significantly up-regulated in the ΔtoxR⁺ strain as compared with the WT⁺ and C-ΔtoxR strains during the early and mid-exponential, while epsG, flaA, flaE, flgD, flgE, flrB, flrC, lpxB, motY, mshA and scrG genes were inhibited because of deletion of the toxR gene in the stationary growth phase. Our results indicate that ToxR plays an important role in controlling the biofilm in V. harveyi.

Healthier Communities of Phytoplankton and Bacteria Achieved via the Application of Modified Clay in Shrimp Aquaculture Ponds

The composition and stability of microbial communities in aquaculture water are crucial for the healthy growth of shrimp and present considerable risk to aquatic ecosystems. The modified clay (MC) method has been proposed as an efficient and safe solution for the mitigation of harmful algal blooms (HABs). Currently, the effects of MC on microbial communities in aquaculture water remain unknown. Here, we adopted the MC method to regulate shrimp-culture water quality and evaluated the effects of MC on the composition and stability of phytoplankton together with bacteria communities through high-throughput sequencing. On the one hand, a prominent change in the composition of microbial community was observed, with green algae becoming the most abundant genera and pathogens being infrequent in the MC-treated pond, which was more conducive to the growth of shrimp than that in the control pond. Moreover, MC could increase the diversity and stability of the microbial community structure in the water column, which had a higher anti-interference ability, as demonstrated by the analysis of the diversity and molecular ecological network. Taken together, MC could reduce the possibility for the occurrence of HABs and maintain a stable microbial community, which is beneficial for the health and high yield of shrimp.

In Vitro Effect of Copper (I) Complex [Cu(NN1)2](ClO4) on Vibrio harveyi BB170 Biofilm Formation

Biofilm formation in pathogenic bacteria is an important factor of resistance to antimicrobial treatments, allowing them to survive for a long time in their hosts. In the search for new antibiofilm agents, in this work we report the activity of a copper (I) complex, [Cu(NN₁)₂]ClO₄, synthesized with Cu (I) and NN1, an imine ligand 6-((quinolin-2-ylmethylene)amino)-2H-chromen-2-one, a derivate of natural compound coumarin. The antibacterial and antibiofilm capacity was evaluated in Vibrio harveyi BB170 used as model bacteria. Antibacterial activity was measured in vitro by minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and half-maximal inhibitory concentration (IC₅₀) determination. Antibiofilm capacity of copper (I) complex was analyzed by different concentrations of IC₅₀ values. The results showed that the sub-IC₅₀ concentration, 12.6 µg/mL of the copper (I) complex, was able to reduce biofilm formation by more than 75%, and bacterial viability was reduced by 50%. Inverted and confocal laser scanning microscopy showed that the [Cu(NN₁)₂]ClO₄ complex affected the biofilm structure. Therefore, the copper (I) complex is effective as an antibiofilm compound in V. harveyi BB170.

Quorum quenching Bacillus spp.: an alternative biocontrol agent for Vibrio harveyi infection in aquaculture

Quorum sensing (QS) is a type of cell to cell communication in bacteria that can also regulate the virulence potential in pathogenic strains. Hence, QS disruption, i.e. the quorum quenching (QQ) mechanism, is presently being explored as a novel bio-control strategy to counter bacterial infections. In the present study, we characterized the QQ ability of Bacillus spp. strains to reduce the expression of some virulence factors of a shrimp pathogen, Vibrio harveyi. We screened a total of 118 spore-forming bacterial isolates from aquaculture ponds and mangrove soil for their ability to degrade the synthetic N-acyl-homoserine lactones (AHLs) C4-HSL, C6-HSL, C8-HSL, and C10-HSL. We then selected the top 17 isolates with high AHL-degradation ability for further study. Among them, B. subtilis MFB10, B. lentus MFB2, and B. firmus MFB7 had the highest ability for degradation. These 3 isolates suppressed the expression of virulence genes encoding protease, lipase, phospholipase, caseinase, chitinase, and gelatinase, and potentially inhibited the biofilm formation of V. harveyi MFB32. The reduction in expression of virulence genes like those coding for metalloprotease, serine protease, and haemolysin were confirmed by real-time PCR analysis. Moreover, in an in vivo challenge experiment, these Bacillus spp. protected Penaeus monodon post-larvae against V. harveyi MFB3 infection. Our results demonstrate the potential application of AHL-degrading Bacillus spp. as an alternative to antibiotics in shrimp hatcheries to control luminescent vibriosis. This novel bio-therapeutic method is a promising approach towards disease control in shrimp aquaculture.

Occurrence of Virulence and Antimicrobial Resistance Determinants in Vibrio harveyi Isolated from Marine Food Fish Cultured in Korea

Vibrio harveyi is a significant cause of infection in both marine animals and humans. It has been reported frequently in seafood-borne infections worldwide. This study was conducted to determine the potential health impact of the V. harveyi isolated from marine food fish cultured in Korea concerning their virulence and antimicrobial resistance. A total of 49 V. harveyi samples were isolated by biochemical tests and multiplex PCR. Phenotypic detection of virulence factors resulted DNase activity (81.63%), hemolysis (α = 75.51% and β = 12.25), gelatinase activity (71.43%), protease production (71.43%), phospholipase activity (65.31%), and lipase production (34.69%). Virulence genes, including VPI, tlh, tdh, toxR, VAC, and ctxAB, were detected in 57.14%, 44.90%, 36.73%, 22.45%, 12.24%, and 8.16% of the isolates, respectively. Resistance to ampicillin (77.55%), oxacillin (69.39%), nalidixic acid (53.06%), amoxicillin (46.94%), oxytetracycline (46.94%), colistin sulfate (34.69%), fosfomycin (34.69%), chloramphenicol (32.65%), streptomycin (32.65%), cephalothin (28.57%), oxytetracycline (26.53%), ceftriaxone (20.41%), erythromycin (14.29%), and cefoxitin (12.24%) was detected in disc diffusion assay. Most of the isolates were classified as multidrug resistant as they scored multiple antimicrobial resistance index ≥0.2. Furthermore, antimicrobial resistance genes tetB, qnrA, intI1 (Class 1 integron integrase), aac(6')-Ib, bla_SHV, bla_CTX-M, strA-strB, tetA, aphAI-IAB, qnrC, qnrS, and bla_TEM were found in 81.63%, 67.35%, 61.22%, 46.94%, 44.90%, 44.90%, 36.73%, 18.37%, 10.20%, 10.20%, 8.16% and 6.12% of the isolates, respectively. In conclusion, the development of antimicrobial resistance among V. harveyi will ultimately reduce the efficacy of antimicrobials used for treating and can favor the development of more virulent V. harveyi strains.

Virulence of Vibrio harveyi ORM4 towards the European abalone Haliotis tuberculata involves both quorum sensing and a type III secretion system

Environmental Vibrio strains represent a major threat in aquaculture, but the understanding of their virulence mechanisms heavily relies on the transposition of knowledge from human-pathogen vibrios. Here, the genetic bases of the virulence of Vibrio harveyi ORM4 towards the European abalone Haliotis tuberculata were characterized. We demonstrated that luxO, encoding a major regulator of the quorum sensing system, is crucial for the virulence of this strain, and that its deletion leads to a decrease in swimming motility, biofilm formation, and exopolysaccharide production. Furthermore, the biofilm formation by V. harveyi ORM4 was increased by abalone serum, which required LuxO. The absence of LuxO in V. harveyi ORM4 yielded opposite phenotypes compared with other Vibrio species including V. campbellii (still frequently named V. harveyi). In addition, we report a full type III secretion system (T3SS) gene cluster in the V. harveyi ORM4 genome. LuxO was shown to negatively regulate the promoter activity of exsA, encoding the major regulator of the T3SS genes, and the deletion of exsA abolished the virulence of V. harveyi ORM4. These results unveil virulence mechanisms set up by this environmentally important bacterial pathogen and pave the way for a better molecular understanding of the regulation of its pathogenicity.

A structural model for (GlcNAc)2 translocation via a periplasmic chitooligosaccharide-binding protein from marine Vibrio bacteria

VhCBP is a periplasmic chitooligosaccharide-binding protein mainly responsible for translocation of the chitooligosaccharide (GlcNAc)₂ across the double membranes of marine bacteria. However, structural and thermodynamic understanding of the sugar-binding/-release processes of VhCBP is relatively less. VhCBP displayed the greatest affinity toward (GlcNAc)₂, with lower affinity for longer-chain chitooligosaccharides [(GlcNAc)_3–4]. (GlcNAc)₄ partially occupied the closed sugar-binding groove, with two reducing-end GlcNAc units extending beyond the sugar-binding groove and barely characterized by weak electron density. Mutation of three conserved residues (Trp³⁶³, Asp³⁶⁵, and Trp⁵¹³) to Ala resulted in drastic decreases in the binding affinity toward the preferred substrate (GlcNAc)₂, indicating their significant contributions to sugar binding. The structure of the W513A–(GlcNAc)₂ complex in a ‘half-open’ conformation unveiled the intermediary step of the (GlcNAc)₂ translocation from the soluble CBP in the periplasm to the inner membrane–transporting components. Isothermal calorimetry data suggested that VhCBP adopts the high-affinity conformation to bind (GlcNAc)₂, while its low-affinity conformation facilitated sugar release. Thus, chitooligosaccharide translocation, conferred by periplasmic VhCBP, is a crucial step in the chitin catabolic pathway, allowing Vibrio bacteria to thrive in oceans where chitin is their major source of nutrients.

Delineating virulence of Vibrio campbellii: a predominant luminescent bacterial pathogen in Indian shrimp hatcheries

Luminescent vibriosis is a major bacterial disease in shrimp hatcheries and causes up to 100% mortality in larval stages of penaeid shrimps. We investigated the virulence factors and genetic identity of 29 luminescent Vibrio isolates from Indian shrimp hatcheries and farms, which were earlier presumed as Vibrio harveyi. Haemolysin gene-based species-specific multiplex PCR and phylogenetic analysis of rpoD and toxR identified all the isolates as V. campbellii. The gene-specific PCR revealed the presence of virulence markers involved in quorum sensing (luxM, luxS, cqsA), motility (flaA, lafA), toxin (hly, chiA, serine protease, metalloprotease), and virulence regulators (toxR, luxR) in all the isolates. The deduced amino acid sequence analysis of virulence regulator ToxR suggested four variants, namely A123Q150 (AQ; 18.9%), P123Q150 (PQ; 54.1%), A123P150 (AP; 21.6%), and P123P150 (PP; 5.4% isolates) based on amino acid at 123rd (proline or alanine) and 150th (glutamine or proline) positions. A significantly higher level of the quorum-sensing signal, autoinducer-2 (AI-2, p = 2.2e-12), and significantly reduced protease activity (p = 1.6e-07) were recorded in AP variant, whereas an inverse trend was noticed in the Q150 variants AQ and PQ. The pathogenicity study in Penaeus (Litopenaeus) vannamei juveniles revealed that all the isolates of AQ were highly pathogenic with Cox proportional hazard ratio 15.1 to 32.4 compared to P150 variants; PP (5.4 to 6.3) or AP (7.3 to 14). The correlation matrix suggested that protease, a metalloprotease, was positively correlated with pathogenicity (p > 0.05) and negatively correlated (p < 0.05) with AI-2 and AI-1. The syntenic organization of toxS-toxR-htpG operon in V. campbellii was found to be similar to pathogenic V. cholerae suggesting a similar regulatory role. The present study emphasizes that V. campbellii is a predominant pathogen in Indian shrimp hatcheries, and ToxR plays a significant role as a virulence regulator in the quorum sensing-protease pathway. Further, the study suggests that the presence of glutamine at 150th position (Q150) in ToxR is crucial for the pathogenicity of V. campbellii.

First insights into a pyruvate sensing and uptake system in Vibrio campbellii and its importance for virulence

Pyruvate is a key metabolite in living cells and has been shown to play a crucial role in the virulence of several bacterial pathogens. The bioluminescent Vibrio campbellii, a severe infectious burden for marine aquaculture, excretes extraordinarily large amounts of pyruvate during growth and rapidly retrieves it by an as-yet unknown mechanism. We have now identified the responsible pyruvate transporter, here named BtsU, and our results show that it is the only pyruvate transporter in V. campbellii. Expression of btsU is tightly regulated by the membrane-integrated LytS-type histidine kinase BtsS, a sensor for extracellular pyruvate, and the LytTR-type response regulator BtsR. Cells lacking either the pyruvate transporter or sensing system show no chemotactic response towards pyruvate, indicating that intracellular pyruvate is required to activate the chemotaxis system. Moreover, pyruvate sensing and uptake were found to be important for the resuscitation of V. campbellii from the viable but nonculturable (VBNC) state and the bacterium's virulence against brine shrimp larvae. IMPORTANCE Bacterial infections are a serious threat to marine aquaculture, one of the fastest growing food sectors on earth. Therefore, it is extremely important to learn more about the pathogens responsible, one of which is Vibrio campbellii. This study sheds light on the importance of pyruvate sensing and uptake for V. campbellii, and reveals that the bacterium possesses only one pyruvate transporter, which is activated by a pyruvate-responsive histidine kinase/response regulator system. Without the ability to sense or take up pyruvate, the virulence of V. campbellii towards gnotobiotic brine shrimp larvae is strongly reduced.

The polar flagellar transcriptional regulatory network in Vibrio campbellii deviates from canonical Vibrio species

Swimming motility is a critical virulence factor in pathogenesis for numerous Vibrio species. Vibrio campbellii DS40M4 is a wild isolate that has been recently established as a highly tractable model strain for bacterial genetics studies. We sought to exploit the tractability and relevance of this strain for characterization of flagellar gene regulation in V. campbellii. Using comparative genomics, we identified homologs of V. campbellii flagellar and chemotaxis genes conserved in other members of the Vibrionaceae and determined the transcriptional profile of these loci using differential RNA-seq. We systematically deleted all 63 predicted flagellar and chemotaxis genes in V. campbellii and examined their effects on motility and flagellum production. We specifically focused on the core regulators of the flagellar hierarchy established in other vibrios: RpoN (σ⁵⁴), FlrA, FlrC, and FliA. Our results show that V. campbellii transcription of flagellar and chemotaxis genes is governed by a multi-tiered regulatory hierarchy similar to other motile Vibrio species. However, there are several critical differences in V. campbellii: (i) the σ⁵⁴-dependent regulator FlrA is dispensable for motility, (ii) the flgA, fliEFGHIJ, flrA, and flrBC operons do not require σ⁵⁴ for expression, and (iii) FlrA and FlrC co-regulate class II genes. Our model proposes that the V. campbellii flagellar transcriptional hierarchy has three classes of genes, in contrast to the four-class hierarchy in Vibrio cholerae. Our genetic and phenotypic dissection of the V. campbellii flagellar regulatory network highlights the differences that have evolved in flagellar regulation across the Vibrionaceae. Importance Vibrio campbellii is a Gram-negative bacterium that is free-living and ubiquitous in marine environments and is an important global pathogen of fish and shellfish. Disruption of the flagellar motor significantly decreases host mortality of V. campbellii, suggesting that motility is a key factor in pathogenesis. Using this model organism, we identified >60 genes that encode proteins with predicted structural, mechanical, or regulatory roles in function of the single polar flagellum in V. campbellii. We systematically tested strains containing single deletions of each gene to determine the impact on motility and flagellum production. Our studies have uncovered differences in the regulatory network and function of several genes in V. campbellii as compared to established systems in Vibrio cholerae and Vibrio parahaemolyticus.

Bacterial diversity in ballast water and sediments revealed by 2b-RAD sequencing

Despite that the ballast water management (BWM) convention has come into force to prevent the spread of harmful aquatic organisms, to date, very few bacteria can be identified through microbial culture method. In this study, we explored a reduced-representation sequencing of 2b-RAD approach to investigate the bacterial diversity in ballast water and sediments (BWS). Our results indicated a large amount of bacteria species (1496) detected in BWS up to now, including 13 pathogens that are seriously concerning in marine environment and aquaculture like the most harmful Vibrio harveyi and Aurantimonas coralicida. We showed that the ballast water had relative lower species, which was dominated by Proteobacteria. In contrast, the sediments had richer species, which was dominated by Bacteroidetes. Although BWS differed significantly in species composition, sediments shared most of the concerned pathogens with ballast water, highlighting the importance of sediment management. In conclusion, 2b-RAD sequencing shows promise in future BWM.

One health pathogen surveillance demonstrated the dissemination of gut pathogens within the two coastal regions associated with intensive farming

BACKGROUND

Intensive aquaculture farming has caused significant degradation of coastal wetlands and has been proposed as a reservoir for pathogenic Vibrio spp.

RESULTS

Gut pathogens including Vibrio spp., Salmonella spp., and Klebsiella spp. were isolated from bird feces, shrimp and wetland water in two typical coastal regions of China in 2015 and 2017 and were subsequently subjected to whole-genome sequencing. Meanwhile, local patient isolates were also selected to confirm the epidemiological links. Bacterial community composition analyses of the sediments that were sampled in 2015 and 2017 were conducted by the hypervariable region 4 of the 16S rRNA gene. Together with the local clinical isolates, we observed highly related Vibrio isolates from waterbirds, wetlands and shrimp. Phylogenetic genome comparisons also demonstrated that sequence types ST3 and ST2414 Vibrio parahaemolyticus isolates obtained from aquatic animals were clonally related to patient isolates. Likewise, three Salmonella typhimurium isolates were also genomically related to one clinical strain. The results showed that farming activities significantly altered the community composition and resulted in the emergence of several pathogens, including Acinetobacter, Mycobacterium and Legionella.

CONCLUSIONS

In conclusion, our results demonstrated that intensive shrimp farming in wetlands has two devastating impacts: pathogen dissemination from aquatic animals into migratory birds and transmission of foodborne pathogens into local communities.

Indole decreases the virulence of pathogenic vibrios belonging to the Harveyi clade

AIM

Indole is a signaling molecule secreted by over 85 species of bacteria, including several Vibrio species, and it has been reported to affect different bacterial phenotypes such as biofilm formation, motility, and virulence. In this study, we aimed at investigating the inter-strain variability of the effect of indole in 12 different strains belonging to the Harveyi clade of vibrios.

METHODS AND RESULTS

Indole reduced the virulence of all strains towards gnotobiotic brine shrimp larvae. The survival rate of brine shrimp larvae challenged with vibrios pretreated with indole was increased by 1.3-fold to 1.8-fold. Additionally, indole significantly decreased the biofilm formation in all of the strains, decreased the swimming motility in eight of the strains, and decreased swarming motility in five of the strains. When cultured in the presence of exogenous indole, the mRNA level of the pirA and pirB toxin genes were down-regulated to 65% and 46%, and to 62% and 55% in the AHPND-causing strains Vibrio parahaemolyticus M0904 and Vibrio campbellii S01, respectively.

CONCLUSIONS

These data indicate that indole has a significant impact on the virulence of different strains belonging to the Harveyi clade of vibrios.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results suggest that indole signaling is a valid target for the development of novel therapeutics in order to control infections caused by Harveyi clade vibrios in aquaculture.

Feeding olive flounder (Paralichthys olivaceus) with Lactococcus lactis BFE920 expressing the fusion antigen of Vibrio OmpK and FlaB provides protection against multiple Vibrio pathogens: A universal vaccine effect

Vibriosis, an illness caused by the Vibrio bacteria species, results in significant economic loss in olive flounder farms. Here we present a novel anti-Vibrio feed vaccine protecting multiple strains of Vibrio pathogens, a universal vaccine effect. The vaccine was generated by engineering Lactococcus lactis BFE920 to express the fusion antigens of Vibrio outer membrane protein K (OmpK) and flagellin B subunit (FlaB). These antigen genes are highly conserved among Vibrio species. Olive flounder (7.1 ± 0.8 g and 140 ± 10 g) were fed the vaccine adsorbed to a regular feed (1 × 10⁷ CFU/g) for one week with a 1-week interval, repeating three times (a triple boost). The vaccinated fish increased the significant levels of antigen-specific antibodies, T cell numbers (CD4-1, CD4-2, and CD8α), cytokine production (T-bet and IFN-γ), and innate immune responses (TLR5M, IL-1β, and IL-12p40). Also, the survival rates of adult and juvenile fish fed the vaccine were significantly elevated when challenged with V. anguillarum, V. alginolyticus, and V. harveyi. In addition, weight gain rate and feed conversion ratio were improved in vaccinated fish. The feed vaccine protected multiple Vibrio pathogens, a universal vaccine effect, by activating innate and adaptive immune responses. This oral vaccine may be developed as an anti-Vibrio vaccine to protect against a broad spectrum of Vibrio pathogens.

Metagenomic Insights Into the Structure and Function of Intestinal Microbiota of the Hadal Amphipods

Hadal trenches are the deepest known areas of the ocean. Amphipods are considered to be the dominant scavengers in the hadal food webs. The studies on the structure and function of the hadal intestinal microbiotas are largely lacking. Here, the intestinal microbiotas of three hadal amphipods, Hirondellea gigas, Scopelocheirus schellenbergi, and Alicella gigantea, from Mariana Trench, Marceau Trench, and New Britain Trench, respectively, were investigated. The taxonomic analysis identified 358 microbial genera commonly shared within the three amphipods. Different amphipod species possessed their own characteristic dominant microbial component, Psychromonas in H. gigas and Candidatus Hepatoplasma in A. gigantea and S. schellenbergi. Functional composition analysis showed that “Carbohydrate Metabolism,” “Lipid Metabolism,” “Cell Motility,” “Replication and Repair,” and “Membrane Transport” were among the most represented Gene Ontology (GO) Categories in the gut microbiotas. To test the possible functions of “Bacterial Chemotaxis” within the “Cell Motility” category, the methyl-accepting chemotaxis protein (MCP) gene involved in the “Bacterial Chemotaxis” pathway was obtained and used for swarming motility assays. Results showed that bacteria transformed with the gut bacterial MCP gene showed significantly faster growths compared with the control group, suggesting MCP promoted the bacterial swimming capability and nutrient utilization ability. This result suggested that hadal gut microbes could promote their survival in poor nutrient conditions by enhancing chemotaxis and motility. In addition, large quantities of probiotic genera were detected in the hadal amphipod gut microbiotas, which indicated that those probiotics would be possible contributors for promoting the host’s growth and development, which could facilitate adaptation of hadal amphipods to the extreme environment.

A novel substituted derivative of sterol from marine actinomycetes Nocardiopsis alba MCCB 110 antagonistic to the aquaculture pathogen Vibrio harveyi

In an attempt to screen antagonistic microorganisms from marine environment for the management of bacterial pathogens in aquaculture, an isolate of actinomycete MCCB 110 was segregated based on its comparatively higher inhibitory property on Vibrio harveyi (MCCB 111) and profound luminescent inhibition. Based on the culture characteristics, cell wall fatty acid profile and the nucleotide sequence of the 16S rRNA gene (1495 bp), the isolate was identified as Nocardiopsis alba. Solvent extraction of the fermentation broth followed by TLC and HPLC analyses resulted in the isolation of a major fraction active against luminescent Vibrio harveyi. Partial characterization of this bioactive fraction based on spectroscopic data obtained from FT-IR, UV, MS-MS and ¹H NMR analyses identified it as a substituted derivative of sterol, and was recognized to differ from those reportedly produced by the same genus. The fraction was not toxic to VERO cell line and shrimp haemocytes up to 1000 ppm tested. The study demonstrated the potential of the putative probiotic Nocardiopsis alba (MCCB 110) and its novel extra-cellular bioactive product in the management of Vibrio harveyi in aquaculture.

Fish farm effluents as a source of antibiotic resistance gene dissemination on Jeju Island, South Korea

The abuse or misuse of antibiotics is directly linked to the emergence of antibiotic-resistant bacteria and antibiotic resistance genes (ARGs) in the environment. Most fish farms located on Jeju Island operate a flow-through system that pumps in seawater for fish farming and discharges it back to the ocean. To investigate the amount of ARGs that these fish farm effluents discharge into the marine environment, we conducted a metagenomic-based resistome analysis. We observed higher levels of ARGs in fish farm effluents than in seawater at beach and residential areas. A greater proportion of ARGs was found on plasmid rather than on chromosomal DNA, especially for sulfonamide and phenicol classes. The distribution of ARGs did not differ between summer and winter, but the microbial community did. In addition, fish farm samples contained significantly more opportunistic pathogens (i.e., Vibrio, Photobacterium, Aliivibrio, and Tenacibaculum) and virulence factors than non-fish farm samples. Vibrio was the most frequently identified host of ARGs and virulence factors. The presence of Vibrio in the coastal area has been increasing owing to the recent rise in the temperature of seawater. This study suggests the need for actions to treat or monitor ARGs in the coastal areas where fish farms operating a flow-through system are located.

Antimicrobial Power of Organic Acids and Nature-Identical Compounds against Two Vibrio spp.: An In Vitro Study

Vibrosis is one of the major threats in aquaculture farming, and due to the increasing antimicrobial resistance of different Vibrio species, there is an urgent need to replace conventional treatments with more sustainable solutions. Antimicrobial molecules such as organic acids (OA) and nature-identical compounds (NIC) are currently finding a central role in the infection management of terrestrial livestock, but little is known about their usage in aquaculture. The aim of this study was to perform a preliminary screening of the in vitro antimicrobial activity of a wide panel of OA and NIC against 2 Vibrio species characteristic of the Mediterranean area, Vibrio harveyi and Vibrio anguillarum, through minimal inhibitory/bactericidal concentration tests. The active principles that showed the best effective pathogen control were medium-chain fatty acids, sorbic and benzoic acid among OA and phenolic monoterpenoids (thymol, carvacrol and eugenol) and aromatic monoterpene aldehydes (vanillin and cinnamaldehyde) among NIC. These results showed how the usage of OA and NIC can open promising perspectives in terms of Vibrio spp. load control in aquaculture. Natural or nature-identical feed additives can make aquaculture production not only more efficient by reducing the need for medicated treatments, but also more sustainable.

Mass mortality in endangered fan mussels Pinna nobilis (Linnaeus 1758) caused by co-infection of Haplosporidium pinnae and multiple Vibrio infection in Çanakkale Strait, Turkey

PURPOSE

Pinna nobilis (fan mussel) is one of the most important endemic bivalve molluscs in the Mediterranean and mass mortality events were observed in these mussels in recent years. In this study, we report mass mortalities caused by Haplosporidium pinnae, which has been spreading in the Mediterranean for 3 years, and reached the Çanakkale Strait, which is the entrance of the Marmara and the Black Sea.

MATERIAL AND METHODS

Field observations during sampling and subsequent histopathological, biochemical, genetic, and microbiological analyses were carried out.

RESULTS

These analyses showed that H. pinnae infection spread among the natural beds of P. nobilis, causing severe tissue damage and oxidative stress. Our phylogenetic analyses suggested that the parasite spread through the Mediterranean much faster than thought. The results showed that vibriosis originating from Vibrio coralliilyticus, Vibrio tubiashii, Vibrio mediterranei, and Vibrio hispanicus, acted together with H. pinnae in infected individuals and caused death.

CONCLUSION

It is highly probable that the spread of H. pinnae to the Sea of Marmara and the Black Sea may occur earlier than expected, and it was concluded that mass deaths were caused by co-infection with H. pinnae and a geographically specific marine pathogen that can infect P. nobilis populations.

Virulence properties and pathogenicity of multidrug-resistant Vibrio harveyi associated with luminescent vibriosis in pacific white shrimp, Penaeus vannamei

Global high demand for pacific white shrimp Penaeus vannamei has led to intensified cultivation and a wide range of disease problems, including bacterial diseases due to vibrios. Three presumptive luminescent Vibrio harveyi strains (Vh5, Vh8 and Vh10) were isolated from the hepatopancreas (Vh5) and haemolymph (Vh8 and Vh10) of diseased growout pacific white shrimp from a farm in Setiu, Terengganu, Malaysia, using Vibrio harveyi agar (VHA) differential medium. All three strains were identified as V. harveyi by biochemical characteristics. 16S rRNA gene-based phylogenetic analyses by neighbour-joining, maximum likelihood and maximum parsimony methods showed all three strains in the V. harveyi cluster. All three strains were β-haemolytic and positive for motility, biofilm formation and extracellular products (caseinase, gelatinase, lipase, DNase, amylase and chitinase). Vh10 was subjected to pathogenicity test in pacific white shrimp by immersion challenge and determined to have a LC₅₀ of 6.0 × 10⁸ CFU mL^-1 after 168 h of exposure. Antibiotic susceptibility tests showed that all strains were resistant to oxytetracycline (OXT30), oleandomycin (OL15), amoxicillin (AML25), ampicillin (AMP10) and colistin sulphate (CT25) but sensitive to doxycycline (DO30), flumequine (UB30), oxolinic acid (OA2), chloramphenicol (C30), florfenicol (FFC30), nitrofurantoin (F5) and fosfomycin (FOS50). Each strain was also resistant to a slightly different combination of eight other antibiotics, with an overall multiple antibiotic resistance (MAR) index of 0.40, suggesting prior history of heavy exposure to the antibiotics. Vh10 infection resulted in pale or discoloured hepatopancreas, empty guts, reddening, necrosis and luminescence of uropods, as well as melanized lesions in tail muscle. Histopathological examination showed necrosis of intertubular connective tissue and tubule, sloughing of epithelial cells in hepatopancreatic tubule, haemocytic infiltration, massive vacuolation and loss of hepatopancreatic tubule structure.

microRNA-210 and microRNA-3570 Negatively Regulate NF-κB-Mediated Inflammatory Responses by Targeting RIPK2 in Teleost Fish

Pathogen infection can cause the production of inflammatory cytokines, which are key mediators that cause the host’s innate immune response. Therefore, proper regulation of immune genes associated with inflammation is essential for immune response. Among them, microRNAs (miRNAs) as gene regulator have been widely reported to be involved in the innate immune response of mammals. However, the regulatory network in which miRNAs are involved in the development of inflammation is largely unknown in lower vertebrates. Here, we identified two miRNAs from miiuy croaker (Miichthys miiuy), miR-210 and miR-3570, which play a negative regulatory role in host antibacterial immunity. We found that the expressions of miR-210 and miR-3570 were significantly upregulated under the stimulation of Gram-negative bacterium vibrio harveyi and LPS (lipopolysaccharide). Induced miR-210 and miR-3570 inhibit inflammatory cytokine production by targeting RIPK2, thereby avoiding excessive inflammation. In particular, we found that miR-210 and miR-3570 negatively regulate antimicrobial immunity by regulating the RIPK2-mediated NF-κB signaling pathway. The collective results indicated that both miRNAs are used as negative feedback regulators to regulate RIPK2-mediated NF-κB signaling pathway and thus play a regulatory role in bacteria-induced inflammatory response.

Thermal Stress Interacts With Surgeonfish Feces to Increase Coral Susceptibility to Dysbiosis and Reduce Tissue Regeneration

Dysbiosis of coral microbiomes results from various biotic and environmental stressors, including interactions with important reef fishes which may act as vectors of opportunistic microbes via deposition of fecal material. Additionally, elevated sea surface temperatures have direct effects on coral microbiomes by promoting growth and virulence of opportunists and putative pathogens, thereby altering host immunity and health. However, interactions between these biotic and abiotic factors have yet to be evaluated. Here, we used a factorial experiment to investigate the combined effects of fecal pellet deposition by the widely distributed surgeonfish Ctenochaetus striatus and elevated sea surface temperatures on microbiomes associated with the reef-building coral Porites lobata. Our results showed that regardless of temperature, exposure of P. lobata to C. striatus feces increased alpha diversity, dispersion, and lead to a shift in microbial community composition – all indicative of microbial dysbiosis. Although elevated temperature did not result in significant changes in alpha and beta diversity, we noted an increasing number of differentially abundant taxa in corals exposed to both feces and thermal stress within the first 48h of the experiment. These included opportunistic microbial lineages and taxa closely related to potential coral pathogens (i.e., Vibrio vulnificus, Photobacterium rosenbergii). Some of these taxa were absent in controls but present in surgeonfish feces under both temperature regimes, suggesting mechanisms of microbial transmission and/or enrichment from fish feces to corals. Importantly, the impact to coral microbiomes by fish feces under higher temperatures appeared to inhibit wound healing in corals, as percentages of tissue recovery at the site of feces deposition were lower at 30°C compared to 26°C. Lower percentages of tissue recovery were associated with greater relative abundance of several bacterial lineages, with some of them found in surgeonfish feces (i.e., Rhodobacteraceae, Bdellovibrionaceae, Crocinitomicaceae). Our findings suggest that fish feces interact with elevated sea surface temperatures to favor microbial opportunism and enhance dysbiosis susceptibility in P. lobata. As the frequency and duration of thermal stress related events increase, the ability of coral microbiomes to recover from biotic stressors such as deposition of fish feces may be greatly affected, ultimately compromising coral health and resilience.

Vibrio harveyi isolated from marine aquaculture species in eastern China and virulence to the large yellow croaker (Larimichthys crocea)

AIMS

Diseases of maricultured species caused by Vibrio harveyi are increasing in China and other regions. This study examined the genetic diversity, antimicrobial susceptibility, plasmid profiles and virulence potential of the V. harveyi isolated from marine organisms farmed in two provinces in eastern China between 2014 and 2019.

METHODS AND RESULTS

A total of 54 V. harveyi were obtained from seven marine species. Enterobacterial repetitive intergenic consensus (ERIC)-PCR fingerprinting revealed substantial genetic heterogeneity among the V. harveyi isolates. There was no significant correlation between ERIC-PCR genotypes and host origins or fish farms. All the isolates were resistant to amoxicillin and ampicillin, and 79·6% to kanamycin. We found that 61·1% of the V. harveyi isolates had plasmid(s) and there were 14 different plasmid profiles. Most isolates from fish hosts (76·5%) contained plasmids; however, 75% of isolates from nonfish hosts lacked plasmids. Experimental infection results showed that isolates with plasmid(s) were more virulent to large yellow croaker than isolates lacking plasmids (P < 0·05).

CONCLUSIONS

This study confirmed that V. harveyi isolates obtained from animals farmed in the coastal region of east China were genetically diverse. Our results suggest that the virulence of various V. harveyi strains to fish is associated with the plasmids they carry.

SIGNIFICANCE AND IMPACT OF THE STUDY

More than 50% of the V. harveyi isolates carried one to 11 plasmids. The plasmid-borne traits of V. harveyi strains might be important for host adaptation and virulence, but they were not associated with susceptibility to the tested antibiotics.

Effects of the Monomeric Components of Poly-hydroxybutyrate-co-hydroxyhexanoate on the Growth of Vibrio penaeicida In Vitro and on the Survival of Infected Kuruma Shrimp (Marsupenaeus japonicus)

Here, we investigated the inhibitory effects of the biodegradable, water-insoluble polymer poly-hydroxybutyrate-co-hydroxyhexanoate (PHBH) and its two constituent monomers, the hydroxyalkanoic acids 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HH), on the growth of the shrimp-pathogenic bacterium Vibrio penaeicida. In vitro experiments revealed that 3HH showed greater growth inhibitory activity than 3HB against V. penaeicida. In addition, the activities of hydroxyalkanoic acids were pH dependent, being greater at pH 6.0 than at pH 7.0. Investigation of the pH of the shrimp gut revealed a pH range of 5.9-6.7 (mean 6.29 ± SD 0.20), indicating that the physiological environment was suitable for 3HB and 3HH to exert their inhibitory activities against V. penaeicida. In vivo bacterial challenge experiments revealed that survival rates in kuruma shrimp (Marsupenaeus japonicus) infected by V. penaeicida were significantly increased in shrimp reared on feed containing PHBH (0.1%-5% w/w PHBH) compared with that in shrimp reared on standard diet alone. Supplementation with PHBH had no significant effects on three shrimp growth parameters: increase in body weight, daily feeding rate, and feed conversion ratio. These results suggest that supplementation of standard diet with PHBH will increase shrimp resistance to infection by V. penaeicida, thereby increasing shrimp aquaculture productivity.

Old problems and new solutions: antibiotic alternatives in food animal production

The antimicrobial resistance crisis is a Global Health challenge that impacts humans, animals, and the environment alike. In response to increased demands for animal protein and by-products, there has been a substantial increase in the use of antimicrobial agents in the animal industry. Indeed, they are extensively used to prevent, control, and (or) treat disease in animals. In addition to infection control, in-feed supplementation with antimicrobials became common practice for growth promotion of livestock. Unfortunately, the global overuse of antimicrobials has contributed to the emergence and spread of resistance. As such, many countries have implemented policies and approaches to eliminate the use of antimicrobials as growth promoters in food animals, which necessitates the need for alternate and One Health strategies to maintain animal health and welfare. This review summarizes the antimicrobial resistance crisis from Global Health and One Health perspectives. In addition, we outline examples of potential alternate strategies to circumvent antimicrobial use in animal husbandry practices, including antivirulence agents, bacteriophages, and nutritional measures to control bacterial pathogens. Overall, these alternate strategies require further research and development efforts, including assessment of efficacy and the associated development, manufacturing, and labor costs.

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.

A First Report of Aeromonas veronii Infection of the Sea Bass, Lateolabrax maculatus in China

The sea bass, Lateolabrax maculatus is commercially farmed in Zhuhai, located in the Guangdong Province of China. L. maculatus in aquaculture have suffered acute death, characterized by ulcerations on the body surface, congestion, and hemorrhage in internal organs such as liver, kidney, and spleen. The dominant infecting strain of bacteria isolated from the kidneys of diseased fish was identified as Aeromonas veronii (strain 18BJ181). This identification was based on analysis of morphological, physiological, and biochemical features, as well as 16S rRNA and gyrB gene sequences. Drug sensitivity testing showed that the strain 18BJ181 isolate was resistant to four antibacterial drugs, including amoxicillin, madinomycin, penicillin and sulfamethoxazole, while moderately sensitive to erythromycin and rifampicin. The detection of growth characteristics showed that the strain 18BJ181 exhibited adaptability to the environment. In addition, some virulence genes, such as aer, act, gcaT, tapA and fla, were detected in the strain 18BJ181. The median lethal dosage of the strain 18BJ181 isolate in L. maculatus was 8.5 × 10⁵ and 4.2 × 10⁵ cfu/g under the conditions of intraperitoneal injection and intramuscular injection, respectively. The experimentally induced infection showed that the 18BJ181 isolate caused considerable histological lesions in L. maculatus, including tissue degeneration, necrosis, and different degrees of hemorrhage. These results provided evidence for a more comprehensive understanding of A. veronii strain 18BJ181 infection in L. maculatus.

Significant Differences in Intestinal Microbial Communities in Aquatic Animals from an Aquaculture Area

While much attention has been given to the role of animal intestinal microbes, few studies have focused on microbial communities and associated functions in cultured aquatic animals. In this study, high–throughput sequencing was used to analyze intestinal microbial communities and functions in fish, shrimp, crab and razor clams. Alpha diversity analyses showed significant differences in intestinal microbial diversity amongst these aquatic animals, and that shrimp intestines harbored the highest diversity and species numbers. T–test analyses (p < 0.05) showed significant differences in dominant microbial operational taxonomic units (OTUs) between all aquatic animals. Predominant intestinal bacteria included; Gammaproteobacteria, Fusobacteria, Mollicutes, Spirochaetia, Cyanobacteria, Bacteroidia and Bacilli. Similarly, anaerobic bacteria were highly diverse in animal intestines and included; Vibrio, Photobacterium, Cetobacterium, Propionigenium, Candidatus Hepatoplasma, Paraclostridium, and Lactobacillus. Principal co–ordinate analysis indicated that the distribution characteristics of intestinal microbes varied with animal species; in particular, we observed a high variability among shrimp intestinal samples. This variability indicated these genera had suitability for the different intestinal environment. Function prediction analysis indicated significant differences amongst different animals in the major functional groups, and that microbial functional profiles were strongly shaped by the intestinal environment. Thus, this study provides an important reference for future studies investigating crosstalk between aquatic animal hosts and their intestinal microbiota.

Impact of a reduced water salinity on the composition of Vibrio spp. in recirculating aquaculture systems for Pacific white shrimp (Litopenaeus vannamei) and its possible risks for shrimp health and food safety

Tropical shrimp, like Litopenaeus vannamei, in land-based recirculating aquaculture systems (RAS) are often kept at low water salinities to reduce costs for artificial sea salt and the amount of salty wastewater. Although these shrimp are tolerant against low salinities, innate immunity suppression and changes in the microbial composition in the water can occur. As especially Vibrio spp. are relevant for shrimp health, alterations in the species composition of the Vibrio community were analysed in water from six RAS, run at 15‰ or 30‰. Additionally, pathogenicity factors including pirA/B, VPI, toxR, toxS, vhh, vfh, tdh, trh, flagellin genes and T6SS1/2 of V. parahaemolyticus were analysed. The Vibrio composition differed significantly depending on water salinity. In RAS at 15‰, higher numbers of the potentially pathogenic species V. parahaemolyticus, V. owensii and V. campbellii were detected, and especially in V. parahaemolyticus, various pathogenicity factors were present. A reduced salinity may therefore pose a higher risk of disease outbreaks in shrimp RAS. Because some of the detected pathogenicity factors are relevant for human health, this might also affect food safety. In order to produce healthy shrimp as a safe food for human consumption, maintaining high water salinities seems to be recommendable.

Applications of bioluminescence in biotechnology and beyond

Bioluminescent probes have hugely benefited from the input of synthetic chemistry and protein engineering. Here we review the latest applications of these probes in biotechnology and beyond, with an eye on current limitations and future directions.

Transcription profile, NF-ĸB promoter activation, and antiviral activity of Amphiprion clarkii Akirin-2

Animal defense system constitutes a series of distinct mechanisms that specifically defend against microbial invasion. Understanding these complex biological mechanisms is of paramount importance for implementing disease prevention strategies. In this study, the transcription factor, Akirin-2 was identified from ornamental fish Amphiprion clarkii and its involvement in immune response was characterized. A. clarkii Akirin-2 (AcAkirin-2) was identified as a highly conserved protein with two nuclear localization signals. In-vitro localization analysis in fathead minnow cells revealed that AcAkirin-2 is strictly localized to the nucleus. With regard to tissue-specific expression without immune challenge, AcAkirin-2 expression was highest in the brain and lowest in the liver. Immune challenge experiments revealed that AcAkirin-2 expression was the strongest in response to poly I:C. Overexpression of AcAkirin-2 alone did not enhanced NF-ĸB activity significantly in HEK293T cells; however, it significantly enhanced NF-ĸB activity in the presence of poly I:C. AcAkirin-2-mediated expression of antiviral genes was analyzed using qPCR in mullet kidney cells and plaque assay was performed to decipher the involvement of AcAkirin-2 in antiviral immunity. AcAkirin-2 overexpression significantly enhanced the expression of Viperin but not of Mx. Plaque assays revealed the ability of AcAkirin-2 to enervate VHSV titers. Taken together, this study unveiled the involvement of AcAkirin-2 in NF-ĸB-mediated transcription of antiviral genes.

β-Sitosterol: An Antibacterial Agent in Aquaculture Management of Vibrio Infections

This study aims at investigation of antibacterial property of Parthenium hysterophorous against aquatic bacterial pathogens and to identify the key bioactive compound of the same. Antibacterial activity of the crude extracts confirmed that chloroform extract PHC has strong antibacterial activity against aquatic pathogens V.anguillarum and V.harveyi with 16mm and 15mm ZOI at 1mg/well concentration. The crude extracts were subjected for GC-MS analysis to identify the secondary metabolites. PHC was subjected to silica-gel column chromatography to separate the individual phytochemicals. PHC was separated into 9 fractions, among which Fraction No.2 demonstrated significant antibacterial activity against V.anguillarum and V.harveyi with 19mm and 17mm ZOI at 10µg/well concentration. Fraction No.2 was identified to be β-sitosterol based on mass spectrometry analysis and fragmentation analysis. In-silico protein ligand docking demonstrated that β-sitosterol has highest affinity to inhibit dihydrofolate reductase (DHFR) enzyme with -10.10Kcal/mol binding energy. This prediction was further validated using molecular dynamic simulation for 20ns. Based on these computational analyses, it was proposed that β-sitosterol exhibits antibacterial activity via inhibition of DHFR enzyme. β-sitosterol is a well known nutritionally valuable compound that reduces cholesterol levels in humans. It is also been used as supplement feed to increase the nutritional value of cultured fishes. β-sitosterol has also been proven to have positive effect in growth and reproduction of cultivated fishes. Findings of this study strongly suggest the usage of β-sitosterol in aquaculture, as nutritional supplement and also as disease control agent to prevent and control fish diseases caused by Vibrio species.

Probiotic Shewanella putrefaciens (SpPdp11) as a Fish Health Modulator: A Review

Aquaculture is considered one of the largest food production sectors in the world. Probiotics have long been considered as a beneficial tool in this industry since these microorganisms improve the welfare of different fish species by modulating several physiological functions, such as metabolism, digestion, immune response, stress tolerance, and disease resistance, among others. SpPdp11, a probiotic isolated from the skin of healthy gilthead seabream, has been the center of attention in a good number of studies since its discovery. The purpose of this paper is to summarize, comment, and discuss the current knowledge related to the effects of SpPdp11 in two commercially important fish species in aquaculture (gilthead seabream and Senegalese sole). Furthermore, some considerations for future studies are also indicated.

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.

Alterations in the Gut Microbiota of Zebrafish (Danio rerio) in Response to Water-Soluble Crude Oil Components and Its Mixture With a Chemical Dispersant

Crude oil spills have caused substantial impacts to aquatic ecosystems. Chemical dispersants are used to palliate the impact of oil spillages, but their use is polemic due to their additional potential toxic effect when mixed with oil-derived components. In this work, we used a 16S-based metagenomic approach to analyze the changes of the gut microbiota of adult zebrafish (Danio rerio) exposed to the water accommodated fraction (WAF) of a light crude oil (35° API gravity), and the chemically enhanced WAF (CEWAF), prepared with Nokomis 3-F4® dispersant. After 96 h of exposure, WAF induced an increase in the alpha and beta diversity, altering the relative abundance of Vibrio, Flavobacterium, and Novosphingobium. In contrast, CEWAF only caused an increase in the beta diversity, and an enrichment of the genus Pseudomona. Both treatments diminished the abundances of Aeromonas, Cetobacterium, Coxiella, Dinghuibacter, and Paucibacter. Moreover, the co-occurrence network among genera was more complex in WAF than in CEWAF, indicating a greater bacterial interaction in response to WAF. Our results indicate that short-term exposure to WAF and CEWAF can induce a dysbiosis in the gut microbiota of D. rerio, but these changes are specific in each treatment.

Rapid Identification of Vibrio Species of the Harveyi Clade Using MALDI-TOF MS Profiling With Main Spectral Profile Database Implemented With an In-House Database: Luvibase

Vibrio bacteria, and particularly members of the Harveyi clade, are the causative agents of vibriosis. This disease is responsible for mass mortality events and important economic losses on aquaculture farms. Improvements in surveillance and diagnosis are needed to successfully manage vibriosis outbreaks. 16S rRNA gene sequencing is generally considered to be the gold standard for bacterial identification but the cost and long processing time make it difficult to apply for routine identification. In contrast, MALDI-TOF MS offers rapid diagnosis and is commonly used in veterinary laboratories today. The major limiting factor for using this technique is the low environmental bacterial diversity in the commonly available databases. Here, we demonstrate that the sole use of the commercially available Bruker BioTyper database is not fully adequate for identifying Vibrio bacteria isolated from aquaculture farms. We therefore developed a new in-house database named Luvibase, composed of 23 reference MALDI-TOF mass spectra profiles obtained from Vibrio collection strains, mostly belonging to the Harveyi clade. The comparison of the accuracy of MALDI-TOF MS profiling and 16S rRNA gene sequencing revealed a lack of resolution for 16S rRNA gene sequencing. In contrast, MALDI-TOF MS profiling proved to be a more reliable tool for resolving species-level variations within the Harveyi clade. Finally, combining the Luvibase with the Bruker ver.9.0.0.0 database, led to successful identification of 47 Vibrio isolates obtained from moribund abalone, seabass and oysters. Thus, the use of Luvibase allow for increased confidence in identifying Vibrio species belonging to the Harveyi clade.