Bacteriophages to control Vibrio alginolyticus in live feeds prior to their administration in larviculture.

AIMS: This study aimed to evaluate the efficiency of two phages [VB_VaC_TDDLMA (phage TDD) and VB_VaC_SRILMA (phage SRI)] alone and in a cocktail to control Vibrio alginolyticus in brine shrimp before their administration in larviculture. METHODS AND RESULTS: Phages were isolated from seawater samples and characterized by host spectrum, growth parameters, adsorption rate, genomic analysis, and inactivation efficiency. Both phages belong to the Caudoviricetes class and lack known virulence or antibiotic-resistance genes. They exhibit specificity, infecting only their host, V. alginolyticus CECT 521. Preliminary experiments in a culture medium showed that phage TDD (reduction of 5.8 log CFU ml-1 after 10 h) outperformed phage SRI (reduction of 4.6 log CFU ml-1 after 6 h) and the cocktail TDD/SRI (reduction of 5.2 log CFU ml-1 after 8 h). In artificial marine water experiments with Artemia franciscana, both single phage suspensions and the phage cocktail, effectively inactivated V. alginolyticus in culture water (reduction of 4.3, 2.1, and 1.9 log CFU ml-1 for phages TDD, SRI, and the phage cocktail, respectively, after 12 h) and in A. franciscana (reduction of 51.6%, 87.3%, and 85.3% for phages TDD, SRI, and the phage cocktail, respectively, after 24 h). The two phages and the phage cocktail did not affect A. franciscana natural microbiota or other Vibrio species in the brine shrimp. CONCLUSIONS: The results suggest that phages can safely and effectively control V. alginolyticus in A. franciscana prior to its administration in larviculture.

Probiotics from kefir: Evaluating their immunostimulant and antioxidant potential in the carpet shell clam (Ruditapesdecussatus).

This study aimed to investigate the impact of incorporating kefir into the diet on biometric parameters, as well as the immune and antioxidant responses of the carpet shell clam (Ruditapes decussatus) after an experimental infection by Vibrio alginolyticus. Clams were divided into a control group and a treated group. The control group was fed on spirulina (Arthrospira platensis) alone. While, the treated group was fed on spirulina supplemented with 10% dried kefir. After 21 days, clams were immersed in a suspension of V. alginolyticus 5 × 105 CFU mL -1 for 30 min. Seven days after experimental infection, survival was 100% in both groups. The obtained results showed a slight increase in weight and condition index in clams fed with kefir-supplemented diet for 21 days compared to control clams. Regarding antioxidant responses, the treated group showed higher superoxide dismutase activity compared to the control group. However, the malondialdehyde level was lower in the treated clams than in the control. In terms of immune parameters, the treated group showed slightly elevated activities of phenoloxidase, lysozyme and alkaline phosphatase, whereas a decreased lectin activity was observed compared to the control group. The obtained results suggest that kefir enhanced both the antioxidant and immune response of infected clams.

Genome-wide expanding of genetic evolution and potential pathogenicity in Vibrio alginolyticus.

Vibrio alginolyticus, an emergent species of Vibrio genus, exists in aquatic and marine environments. It has undergone genetic diversification, but its detailed genomic diversity is still unclear. Here, we performed a multi-dimensional comparative genomic analysis to explore the population phylogeny, virulence-related genes and potential drug resistance genes of 184 V. alginolyticus isolates. Although genetic diversity is complex, we analysed the population structure using three sub-datasets, including the subdivision for three lineages into sublineages and the distribution of strains in the marine ecological niche. Accessory genes, most of which reclassified V. alginolyticus genomes as different but with relatively close affinities, were nonuniformly distributed among these isolates. We demonstrated that the spread of some post-evolutionary isolates (mainly L3 strains isolated from Chinese territorial seas) was likely to be closely related to human activities, whereas other more ancestral strains (strains in the L1 and L2) tended to be locally endemic and formed clonal complex groups. In terms of pathogenicity, the potential virulence factors were mainly associated with toxin, adherence, motility, chemotaxis, and the type III secretion system (T3SS). We also found five types of antibacterial drug resistance genes. The prevalence of ß-lactam resistance genes was 100%, which indicated that there may be a potential risk of natural resistance to ß-lactam drugs. Our study reveals insights into genomic characteristics, evolution and potential virulence-associated gene profiles of V. alginolyticus.

Functional characterization of NOD1 from golden pompano Trachinotus ovatus.

Fish rely on innate immune system for immunity, and nucleotide-binding oligomerization domain-like receptors (NLRs) are a vital group of receptor for recognition. In the present study, NOD1 gene was cloned and characterized from golden pompano Trachinotus ovatus, a commercially important aquaculture fish species. The ORF of T. ovatus NOD1 was 2820 bp long, encoding 939 amino acid residues with a highly conserved domains containing CARD-NACHT-LRRs. Phylogenetic analysis revealed that the T. ovatus NOD1 clustered with those of fish and separated from those of birds and mammals. T. ovatus NOD1 has wide tissue distribution with the highest expression in gills. Bacterial challenges (Streptococcus agalactiae and Vibrio alginolyticus) significantly up-regulated the expression of NOD1 with different response time. The results of T. ovatus NOD1 ligand recognition and signaling pathway analysis revealed that T. ovatus NOD1 could recognize iE-DAP at the concentration of ≧ 100 ng/mL and able to activate NF-κB signaling pathway. This study confirmed that NOD1 play a crucial role in the innate immunity of T. ovatus. The findings of this study improve our understanding on the immune function of NOD1 in teleost, especially T. ovatus.

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

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

Transcriptome analysis provides new insights into the immune response of Ruditapes philippinarum infected with Vibrio alginolyticus.

Manila clam (Ruditapes philippinarum) is a bivalve species with commercial value, but it is easily infected by pathogenic microorganisms in aquaculture, which restricts the shellfish industry. Notably, the impact of Vibrio alginolyticus on clam culture is obvious. In this study, RNA-seq was performed to analyze clam hepatopancreas tissue in 48 h (challenge group, G48h) and 96 h (challenge group, G96h) after infection with V. alginolyticus and 0 h after injection of PBS (control group, C). The results showed that a total of 1670 differentially expressed genes were detected in the G48h vs C group, and 1427 differentially expressed genes were detected in the G96h vs C group. In addition, KEGG analysis showed that DEGs were significantly enriched in pathways such as Lysosome and Mitophagy. Moreover, 15 immune related DEGs were selected for qRT-PCR analysis to verify the accuracy of RNA-seq, and the results showed that the expression level of DEGs was consistent with that of RNA-seq. Therefore, the results obtained in this study provides a preliminary understanding of the immune defense of R. philippinarum and molecular insights for genetic breeding of V. alginolyticus resistance in Manila clam.

Deciphering the genomes of motility-deficient mutants of Vibrio alginolyticus 138-2.

The motility of Vibrio species plays a pivotal role in their survival and adaptation to diverse environments and is intricately associated with pathogenicity in both humans and aquatic animals. Numerous mutant strains of Vibrio alginolyticus have been generated using UV or EMS mutagenesis to probe flagellar motility using molecular genetic approaches. Identifying these mutations promises to yield valuable insights into motility at the protein structural physiology level. In this study, we determined the complete genomic structure of 4 reference specimens of laboratory V. alginolyticus strains: a precursor strain, V. alginolyticus 138-2, two strains showing defects in the lateral flagellum (VIO5 and YM4), and one strain showing defects in the polar flagellum (YM19). Subsequently, we meticulously ascertained the specific mutation sites within the 18 motility-deficient strains related to the polar flagellum (they fall into three categories: flagellar-deficient, multi-flagellar, and chemotaxis-deficient strains) by whole genome sequencing and mapping to the complete genome of parental strains VIO5 or YM4. The mutant strains had an average of 20.6 (±12.7) mutations, most of which were randomly distributed throughout the genome. However, at least two or more different mutations in six flagellar-related genes were detected in 18 mutants specifically selected as chemotaxis-deficient mutants. Genomic analysis using a large number of mutant strains is a very effective tool to comprehensively identify genes associated with specific phenotypes using forward genetics.

Roles of linker region flanked by transmembrane and peptidoglycan binding region of PomB in energy conversion of the Vibrio flagellar motor.

The flagellar components of Vibrio spp., PomA and PomB, form a complex that transduces sodium ion and contributes to rotate flagella. The transmembrane protein PomB is attached to the basal body T-ring by its periplasmic region and has a plug segment following the transmembrane helix to prevent ion flux. Previously we showed that PomB deleted from E41 to R120 (Δ41-120) was functionally comparable to the full-length PomB. In this study, three deletions after the plug region, PomB (Δ61-120), PomB (Δ61-140), and PomB (Δ71-150), were generated. PomB (Δ61-120) conferred motility, whereas the other two mutants showed almost no motility in soft agar plate; however, we observed some swimming cells with speed comparable for the wild-type cells. When the two PomB mutants were introduced into a wild-type strain, the swimming ability was not affected by the mutant PomBs. Then, we purified the mutant PomAB complexes to confirm the stator formation. When plug mutations were introduced into the PomB mutants, the reduced motility by the deletion was rescued, suggesting that the stator was activated. Our results indicate that the deletions prevent the stator activation and the linker and plug regions, from E41 to S150, are not essential for the motor function of PomB but are important for its regulation.

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.

Application of nZnO supported with nanoclay for improving shrimp immunity.

This study discloses the nanoscale silicate platelet-supported nZnO (ZnONSP) applied as novel feed additives in aquaculture. The preparation of the nanohybrid (ZnO/NSP = 15/85, w/w) was characterized by UV-visible spectroscopy, powder X-ray diffraction and transmission electron microscope. The effects of ZnONSP on growth, zinc accumulation, stress response, immunity and resistance to Vibrio alginolyticus in white shrimp (Penaeus vannamei) were \demonstrated. To evaluate the safety of ZnONSP, shrimps (2.0 ± 0.3 g) were fed with ZnONSP containing diets (200, 400 and 800 mg/kg) for 56 days. Dietary ZnONSP did not affect the weight gain, specific growth rate, feed conversion ratio, survival rate, zinc accumulation, and the expression of heat shock protein 70 in tested shrimps. To examine the immunomodulatory effect of ZnONSP, shrimps (16.6 ± 2.4 g) were fed with the same experimental diets for 28 days. Dietary ZnONSP improved the immune responses of haemocyte in tested shrimps, including phagocytic rate, phagocytic index, respiratory burst, and phenoloxidase activity, and upregulated the expression of several genes, including lipopolysaccharide, ß-1,3-glucan binding protein, peroxinectin, penaeidin 2/3/4, lysozyme, crustin, anti-lipopolysaccharide factor, superoxide dismutase, glutathione peroxidase, clotting protein and α-2-macroglobulin. In the challenge experiment, shrimps (17.2 ± 1.8 g) were fed with ZnONSP containing diets (400 and 800 mg/kg) for 7 days and then infected with Vibrio alginolyticus. Notably, white shrimps that received ZnONSP (800 mg/kg) showed significantly improved Vibrio resistance, with a survival rate of 71.4 % at the end of 7-day observation. In conclusion, this study discovers that ZnONSP is a new type of immunomodulatory supplement that are effective on enhancing innate cellular and humoral immunities, and disease resistance in white shrimp.

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

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

Low-dose of formalin-inactivated Vibrio alginolyticus protects Crassostrea gigas from secondary infection and confers broad-spectrum Vibrio resistance on offspring.

An increasing number of evidences have shown that invertebrate taxa can be primed to produce immune memory to resist the secondary infection of pathogens, which was considered as a viable option to protect invertebrates from pathogens. In this work, we compared the protective effect of several different immune priming methods on the Vibrio alginolyticus secondary infection of the Crassostrea gigas. The results showed that C. gigas primed with live V. alginolyticus had higher ROS level, which led to hemocytes necrosis and higher mortality rate in the later stage. Low-dose of formalin-inactivated V. alginolyticus (including 5 × 104 CFU/mL and 5 × 105 CFU/mL) elicited appropriate immune response in C. gigas, protecting C. gigas from V. alginolyticus infection. Immersion with 5 × 104 CFU/mL formalin-inactivated V. alginolyticus was performed to prime C. gigas immunity in the trans-generational immune priming. Trans-generational immune priming significantly increased the resistance of larvae to various Vibrio species. Overall, these results suggested that low-dose of formalin-inactivated V. alginolyticus can protect C. gigas from secondary infection and confer broad-spectrum Vibrio resistance on offspring. This work provided valuable information toward a new direction for the protection of C. gigas from Vibrio infection.

Transcriptome analysis reveals tissue-specific responses of Mytilus unguiculatus to Vibrio alginolyticus infection.

Mytilus unguiculatus is an important economic bivalve species with wide consumption and aquaculture value. Disease is one of the primary limiting factors in mussel aquaculture, thus understanding the response of different tissues of M. unguiculatus to pathogens is crucial for disease prevention and control. In this study, we investigated the physiological and transcriptomic responses of the gills, adductor muscle, and mantle of M. unguiculatus infected with Vibrio alginolyticus. The results showed that V. alginolyticus infection caused inflammation and tissue structure changes in the gill, adductor muscle and mantle of M. unguiculatus. Meanwhile, the activities of superoxide dismutase and catalase in the three tissues increased, while the total antioxidant capacity decreased, suggesting that M. unguiculatus have an activated defense mechanism against infection-induced oxidative stress, despite a compromised total antioxidant capacity. Transcriptomic studies reveal that infected M. unguiculatus exhibits upregulation of endocytosis, lysosome activity, cellular apoptosis, and immune-related signaling pathways, indicating that M. unguiculatus responds to pathogen invasion by upregulating efferocytosis. Compared with the gill and adductor muscle, the mantle had a higher level of mytimycin, mytilin and myticin, and the three tissues also increased the expression of mytimycin to cope with the invasion of pathogens. In addition, the analysis of genes related to taste transduction pathways and muscle contraction and relaxation found that after infection with V. alginolyticus, M. unguiculatus may reduce appetite by inhibiting taste transduction in the gill, while improving muscle contraction of the adductor muscle and keeping the shell closed, to resist further invasion of pathogens and reduce the risk of pathogen transmission in the population.

Deletion of ArmPT, a LamB-like protein, increases cell membrane permeability and antibiotic sensitivity in Vibrio alginolyticus.

Vibrio bacterial species are dominant pathogens in mariculture animals. However, the extensive use of antibiotics and other chemicals has increased drug resistance in Vibrio bacteria. Despite rigorous investigative studies, the mechanism of drug resistance in Vibrio remains a mystery. In this study, we found that a gene encoding LamB-like outer membrane protein, named ArmPT, was upregulated in Va under antibiotic stress by RT-qPCR. We speculated that ArmPT might play a role in Va's drug resistance. Subsequently, using ArmPT gene knockout and gene complementation experiments, we confirmed its role in resistance against a variety of antibiotics, particularly kanamycin (KA). Transcriptomic and proteomic analyses identified 188 and 83 differentially expressed genes in the mutant strain compared with the wild-type (WT) before and after KA stress, respectively. Bioinformatic analysis predicted that ArmPT might control cell membrane permeability by changing cadaverine biosynthesis, thereby influencing the cell entry of antibiotics in Va. The higher levels of intracellular reactive oxygen species and the infused content of KA showed that antibiotics are more likely to enter the Va mutant strain. These results uncover the drug resistance mechanism of Va that can also exist in other similar pathogenic bacteria.

Transcriptome analysis of the hepatopancreas from the Litopenaeus vannamei infected with different flagellum types of Vibrio alginolyticus strains.

Vibrio alginolyticus, one of the prevalently harmful Vibrio species found in the ocean, causes significant economic damage in the shrimp farming industry. Its flagellum serves as a crucial virulence factor in the invasion of host organisms. However, the processes of bacteria flagella recognition and activation of the downstream immune system in shrimp remain unclear. To enhance comprehension of this, a ΔflhG strain was created by in-frame deletion of the flhG gene in V. alginolyticus strain HN08155. Then we utilized the transcriptome analysis to examine the different immune responses in Litopenaeus vannamei hepatopancreas after being infected with the wild type and the mutant strains. The results showed that the ΔflhG strain, unlike the wild type, lost its ability to regulate flagella numbers negatively and displayed multiple flagella. When infected with the hyperflagella-type strain, the RNA-seq revealed the upregulation of several immune-related genes in the shrimp hepatopancreas. Notably, two C-type lectins (CTLs), namely galactose-specific lectin nattectin and macrophage mannose receptor 1, and the TNF receptor-associated factor (TRAF) 6 gene were upregulated significantly. These findings suggested that C-type lectins were potentially involved in flagella recognition in shrimp and the immune system was activated through the TRAF6 pathway after flagella detection by CTLs.

Rapid visual nucleic acid detection of Vibrio alginolyticus by recombinase polymerase amplification combined with CRISPR/Cas13a.

Vibrio alginolyticus (V. alginolyticus) is a common pathogen in the ocean. In addition to causing serious economic losses in aquaculture, it can also infect humans. The rapid detection of nucleic acids of V. alginolyticus with high sensitivity and specificity in the field is very important for the diagnosis and treatment of infection caused by V. alginolyticus. Here, we established a simple, fast and effective molecular method for the identification of V. alginolyticus that does not rely on expensive instruments and professionals. The method integrates recombinase polymerase amplification (RPA) technology with CRISPR system in a single PCR tube. Using this method, the results can be visualized by lateral flow dipstick (LFD) in less than 50 min, we named this method RPA-CRISPR/Cas13a-LFD. The method was confirmed to achieve high specificity for the detection of V. alginolyticus with no cross-reactivity with similar Vibrio and common clinical pathogens. This diagnostic method shows high sensitivity; the detection limit of the RPA-CRISPR/Cas13a-LFD is 10 copies/µL. We successfully identified 35 V. alginolyticus strains from a total of 55 different bacterial isolates and confirmed their identity by (Matrix-assisted laser desorption ionization time-of-flight mass spectrometry, MALDI-TOF MS). We also applied this method on infected mice blood, and the results were both easily and rapidly obtained. In conclusion, RPA-CRISPR/Cas13a-LFD offers great potential as a useful tool for reliable and rapid diagnosis of V. alginolyticus infection, especially in limited conditions.

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

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

Vibrio alginolyticus growth kinetics and the metabolic effects of iron.

IMPORTANCE: Transmission of V. alginolyticus occurs opportunistically through direct seawater exposure and is a function of its abundance in the environment. Like other Vibrio spp., V. alginolyticus are considered conditionally rare taxa in marine waters, with populations capable of forming large, short-lived blooms under specific environmental conditions, which remain poorly defined. Prior research has established the importance of temperature and salinity as the major determinants of Vibrio geographical and temporal range. However, bloom formation can be strongly influenced by other factors that may be more episodic and localized, such as changes in iron availability. Here we confirm the broad temperature and salinity tolerance of V. alginolyticus and demonstrate the importance of iron supplementation as a key factor for growth in the absence of thermal or osmotic stress. The results of this research highlight the importance of episodic iron input as a crucial metric to consider for the assessment of V. alginolyticus risk.

Genome Sequencing-Based Mining and Characterization of a Novel Alginate Lyase from Vibrio alginolyticus S10 for Specific Production of Disaccharides.

Alginate oligosaccharides prepared by alginate lyases attracted great attention because of their desirable biological activities. However, the hydrolysis products are always a mixture of oligosaccharides with different degrees of polymerization, which increases the production cost because of the following purification procedures. In this study, an alginate lyase, Alg4755, with high product specificity was identified, heterologously expressed, and characterized from Vibrio alginolyticus S10, which was isolated from the intestine of sea cucumber. Alg4755 belonged to the PL7 family with two catalytic domains, which was composed of 583 amino acids. Enzymatic characterization results show that the optimal reaction temperature and pH of Alg4755 were 35 °C and 8.0, respectively. Furthermore, Alg4755 was identified to have high thermal and pH stability. Moreover, the final hydrolysis products of sodium alginate catalyzed by Alg4755 were mainly alginate disaccharides with a small amount of alginate trisaccharides. The results demonstrate that alginate lyase Alg4755 could have a broad application prospect because of its high product specificity and desirable catalytic properties.

Occurrence of virulence determinants in vibrio cholerae, vibrio mimicus, vibrio alginolyticus, and vibrio parahaemolyticus isolates from important water resources of Eastern Cape, South Africa.

BACKGROUND: Virulence determinants are crucial to the risk assessment of pathogens in an environment. This study investigated the presence of eleven key virulence-associated genes in Vibrio cholerae (n = 111) and Vibrio mimicus (n = 22) and eight virulence determinants in Vibrio alginolyticus (n = 65) and Vibrio parahaemolyticus (n = 17) isolated from six important water resources in Eastern Cape, South Africa, using PCR techniques. The multiple virulence gene indexes (MVGI) for sampling sites and isolates as well as hotspots for potential vibriosis outbreaks among sampling sites were determined statistically based on the comparison of MVGI. RESULT: The PCR assay showed that all the V. cholerae isolates belong to non-O1/non-O139 serogroups. Of the isolates, Vibrio Cholera (84%), V. mimicus (73%), V. alginolyticus (91%) and V. parahaemolyticus (100%) isolates harboured at least one of the virulence-associated genes investigated. The virulence gene combinations detected in isolates varied at sampling site and across sites. Typical virulence-associated determinants of V. cholerae were detected in V. mimicus while that of V. parahaemolyticus were detected in V. alginolyticus. The isolates with the highest MVGI were recovered from three estuaries (Sunday river, Swartkopps river, buffalo river) and a freshwater resource (Lashinton river). The cumulative MVGI for V. cholerae, V. mimicus, V. alginolyticus and V. parahaemolyticus isolates were 0.34, 0.20, 0.45, and 0.40 respectively. The targeted Vibrio spp. in increasing order of the public health risk posed in our study areas based on the MVGI is V. alginolyticus > V. parahaemolyticus > V. cholerae > V. mimicus. Five (sites SR, PA5, PA6, EL4 and EL6) out of the seventeen sampling sites were detected as the hotspots for potential cholera-like infection and vibriosis outbreaks. CONCLUSIONS: Our findings suggest that humans having contact with water resources in our study areas are exposed to potential public health risks owing to the detection of virulent determinants in human pathogenic Vibrio spp. recovered from the water resources. The study affirms the relevancy of environmental Vibrio species to the epidemiology of vibriosis, cholera and cholera-like infections. Hence we suggest a monitoring program for human pathogenic Vibrio spp. in the environment most especially surface water that humans have contact with regularly.