The surface display of haemolysin from Vibrio harveyi on yeast cells and their potential applications as live vaccine in marine fish

Oral Vaccination of Largemouth Bass (Micropterus salmoides) against Largemouth Bass Ranavirus (LMBV) Using Yeast Surface Display Technology

Largemouth bass ranavirus (LMBV) infects largemouth bass, leading to significant mortality and economic losses. There are no safe and effective drugs against this disease. Oral vaccines that directly target the intestinal mucosal immune system play an important role in resisting pathogens. Herein, the B subunit of Escherichia coli heat-labile enterotoxin (LTB, a mucosal immune adjuvant) and the LMBV main capsid protein (MCP) were expressed using Saccharomyces cerevisiae surface display technology. The yeast-prepared oral vaccines were named EBY100-OMCP and EBY100-LTB-OMCP. The candidate vaccines could resist the acidic intestinal environment. After 7 days of continuous oral immunization, indicators of innate and adaptive immunity were measured on days 1, 7, 14, 21, 28, 35, and 42. High activities of immune enzymes (T-SOD, AKP, ACP, and LZM) in serum and intestinal mucus were detected. IgM in the head kidney was significantly upregulated (EBY100-OMCP group: 3.8-fold; BY100-LTB-OMCP group: 4.3-fold). IgT was upregulated in the intestines (EBY100-OMCP group: 5.6-fold; EBY100-LTB-OMCP group: 6.7-fold). Serum neutralizing antibody titers of the two groups reached 1:85. Oral vaccination protected against LMBV infection. The relative percent survival was 52.1% (EBY100-OMCP) and 66.7% (EBY100-LTB-OMCP). Thus, EBY100-OMCP and EBY100-LTB-OMCP are promising and effective candidate vaccines against LMBV infection.

Standardization and Key Aspects of the Development of Whole Yeast Cell Vaccines

In the context of vaccine development, improving antigenic presentation is critical for the activation of specific immune responses and the success of immunization, in addition to selecting an appropriate target. In this sense, different strategies have been developed and improved. Among them is the use of yeast cells as vehicles for the delivery of recombinant antigens. These vaccines, named whole yeast vaccines (WYVs), can induce humoral and cellular immune responses, with the additional advantage of dispensing with the use of adjuvants due to the immunostimulatory properties of their cell wall components. However, there are some gaps in the methodologies for obtaining and validating recombinant strains and vaccine formulations. The standardization of these parameters is an important factor for WYVs approval by regulatory agencies and, consequently, their licensing. This review aimed to provide an overview of the main parameters to consider when developing a yeast-based vaccine, addressing some available tools, and highlighting the main variables that can influence the vaccine production process.

Dietary intake of GDF11 delays the onset of several biomarkers of aging in male mice through anti-oxidant system via Smad2/3 pathway

Current studies have generated controversy over the age-related change in concentration of growth differentiation factor 11 (GDF11) and its role in the genesis of rejuvenation conditions. In this study, we displayed rGDF11 on the surface of Yarrowic Lipolytica (Y. lipolytica), and proved the bioavailability of the yeast-displayed rGDF11 by oral delivery in aged male mice. On the basis of these findings, we started to explore the anti-aging activity and underlying mechanisms of displayed rGDF11. It was found that dietary intake of displayed rGDF11 had little influence on the body weight and biochemical parameters of aged male mice, but delayed the occurrence and development of age-related biomarkers such as lipofuscin (LF) and senescence-associated-β-galactosidase, and to some extent, prolonged the lifespan of aged male mice. Moreover, we demonstrated once again that dietary intake of displayed rGDF11 enhanced the activity of anti-oxidant enzymes, including catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPX), reduced the reactive oxygen species (ROS) level, and slowed down the protein oxidation and lipid peroxidation. Importantly, we showed for the first time that rGDF11 enhanced the activity of CAT, SOD and GPX through activation of the Smad2/3 signaling pathway. Our study also provided a simple and safe route for delivery of recombinant GDF11, facilitating its therapeutic application in the future.

Shrimp protected from a virus by feed containing yeast with a surface-displayed viral binding protein

Recombinant Pichia pastoris biomass surface-expressing the viral binding protein PmRab7 (YSD-PmRab7) was prepared by fed-batch, aerobic fermentation with methanol induction for 48 h. By cell based ELISA assay, immunofluorescence and flow cytometry, 45% of the YSD-PmRab7 cells were positive for PmRab7. Freeze dried YSD-PmRab7 cells were added to formulated shrimp feed pellets at 0.25 g and 0.5 g per g feed and fed to 2 shrimp groups for 7 days prior to challenge with white spot syndrome virus (WSSV). Controls consisted of 1 shrimp group fed normal pellets and one fed pellets containing P. pastoris carrying an empty gene cassette. At 10 days post challenge, survival in the two control groups was 6.7 ± 6.6%, while it was 26.7 ± 6.6% in the 0.25 g YSD-PmRab7 group and significantly higher (p < 0.05) in the 0.5 g YSD-PmRab7 group at 46.7 ± 10.1%. Nested PCR assays and histopathological analysis revealed significantly lower WSSV replication levels in the 0.5 g YSD-PmRab7 group. The results indicated potential for development of YSD-PmRab7 cells as an oral prophylactic against WSSV in shrimp.

Vibrio harveyi: a serious pathogen of fish and invertebrates in mariculture

Vibrio harveyi, which belongs to family Vibrionaceae of class Gammaproteobacteria, includes the species V. carchariae and V. trachuri as its junior synonyms. The organism is a well-recognized and serious bacterial pathogen of marine fish and invertebrates, including penaeid shrimp, in aquaculture. Diseased fish may exhibit a range of lesions, including eye lesions/blindness, gastro-enteritis, muscle necrosis, skin ulcers, and tail rot disease. In shrimp, V. harveyi is regarded as the etiological agent of luminous vibriosis in which affected animals glow in the dark. There is a second condition of shrimp known as Bolitas negricans where the digestive tract is filled with spheres of sloughed-off tissue. It is recognized that the pathogenicity mechanisms of V. harveyi may be different in fish and penaeid shrimp. In shrimp, the pathogenicity mechanisms involved the endotoxin lipopolysaccharide, and extracellular proteases, and interaction with bacteriophages. In fish, the pathogenicity mechanisms involved extracellular hemolysin (encoded by duplicate hemolysin genes), which was identified as a phospholipase B and could inactivate fish cells by apoptosis, via the caspase activation pathway. V. harveyi may enter the so-called viable but nonculturable (VBNC) state, and resuscitation of the VBNC cells may be an important reason for vibriosis outbreaks in aquaculture. Disease control measures center on dietary supplements (including probiotics), nonspecific immunostimulants, and vaccines and to a lesser extent antibiotics and other antimicrobial compounds.

Evaluation of cell-surface displayed synthetic consensus dengue EDIII cells as a potent oral vaccine candidate

BACKGROUND

Dengue is a rapidly spreading mosquito borne tropical viral disease affecting hundreds of millions of people across the globe annually. The dengue virus (DENV) includes four genetically distinct serotypes that cause serious life-threatening infections, including dengue hemorrhagic fever/dengue shock syndrome. Dengue vaccine development is complicated by the possibility of vaccine-enhanced severe dengue disease due to antibody-dependent enhancement by pre-existing cross-reactivity, as well as homotypic antibodies. Thus, the development of an efficacious dengue vaccine conferring simultaneous and durable immunity to each of the four DENV serotypes has not yet been developed despite years of research. For mass immunization in deeply affected resource-limited countries, oral vaccination is considered more beneficial than conventional approaches. Therefore, in a continuing effort towards designing economical and potent vaccine candidates, the current study applied yeast surface display technology to develop an oral dengue vaccine candidate using whole recombinant yeast cells displaying the recombinant fusion protein of M cell targeting ligand Co1 fused to the synthetic consensus dengue envelope domain III (scEDIII). Female Balb/c mice were orally fed with recombinant yeast cells and immunogenicity in terms of systemic and mucosal immune responses was monitored.

RESULTS

Immunofluorescence microscopy with dengue specific antibody and fluorescein isothiocyanate-conjugated anti-mouse IgG antibody clearly showed that recombinant protein Co1-scEDIII-AGA was localized on the cell surface of the respective clones in comparison with scEDIII-Co1 and Mock cells with no fluorescence. Oral dosage applications of surface displayed Co1-scEDIII-AGA stimulated a systemic humoral immune response in the form of dengue-specific serum IgG, as well as a mucosal immune response in the form of secretory immunoglobulin A (sIgA). Antigen-specific B cell responses in isolated lymphoid cells from the spleen and Peyer's patches further supported an elevated mucosal immune response. In addition, surface displayed Co1-scEDIII-AGA feeding elicited strong immune responses in comparison with scEDIII-Co1 and Mock following intraperitoneal booster with purified scEDIII antigen.

CONCLUSIONS

Surface displayed preparations of Co1-scEDIII-AGA induced strong immunogenicity compared with non-displayed scEDIII-Co1. Prior studies have supported the neutralization potential of scEDIII constructs against all four serotypes. Thus, the oral administration of genetically engineered yeast whole cells displaying biologically active Co1-scEDIII fusion protein without any further processing shows prospective as a potent oral vaccine candidate against dengue viral infection.

Human Enterovirus 71 Protein Displayed on the Surface of Saccharomyces cerevisiae as an Oral Vaccine

Human enterovirus 71 (EV-A71), a major agent of hand, foot, and mouth disease, has become an important public health issue in recent years. No effective antiviral or vaccines against EV-A71 infection are currently available. EV-A71 infection intrudes bodies through the gastric mucosal surface and it is necessary to enhance mucosal immune response to protect children from these pathogens. Recently, the majority of EV-A71 vaccine candidates have been developed for parenteral immunization. However, parenteral vaccine candidates often induce poor mucosal responses. On the other hand, oral vaccines could induce effective mucosal and systemic immunity, and could be easily and safely administered. Thus, proper oral vaccines have attached more interest compared with parenteral vaccine. In this study, the major immunogenic capsid protein of EV-A71 was displayed on the surface of Saccharomyces cerevisiae. Oral immunization of mice with surface-displayed VP1 S. cerevisiae induced systemic humoral and mucosal immune responses, including virus-neutralizing titers, VP1-specific antibody, and the induction of Th1 immune responses in the spleen. Furthermore, oral immunization of mother mice with surface-displayed VP1 S. cerevisiae conferred protection to neonatal mice against the lethal EV-A71 infection. Furthermore, we observed that multiple boost immunization as well as higher immunization dosage could induce higher EV-A71-specific immune response. Our results demonstrated that surface-displayed VP1 S. cerevisiae could be used as potential oral vaccine against EV-A71 infection.

An efficient and simple method to increase the level of displayed protein on the yeast cell surface

BACKGROUND

The development of oral vaccines using yeast surface display technology is an area of intensive study in vaccine development, but the protein level displayed on yeast surfaces is not currently high enough to obtain a robust immune response.

METHODS

To address this issue, we established an efficient and simple method of increasing the level of displayed protein on the yeast cell surface. We used the single chain variable fragment (scFv) of an antibody against the infectious hematopoietic necrosis virus isolate Sn1203 as a target display protein. The yeast-derived scFv was first displayed on the yeast surface by galactose induction, and then Escherichia coli-derived scFv was also displayed on the same yeast via an artificial anchoring condition to increase the total scFv level on the yeast surface.

RESULTS

The levels of yeast- and E. coli-derived scFv displayed on the yeast cell surface were analyzed by flow cytometry, western blotting, and fluorescent microscopy. The flow cytometry results indicated that when the cells were suspended in phosphate-buffered saline with 1mmol/L glutathione, 0.2mmol/L oxidized glutathione, and 5% dimethyl sulfoxide at 4°C for 6h, the E. coli-derived scFv protein was stably anchored to the yeast cell surface. The mean fluorescence intensity in these experiments, which is an indirect quantitative representation of the surface scFv expression, was three times higher in the treated cells than that in control cells. The western blotting results show two specific protein bands, the smaller of which was identified as the E. coli-derived scFv that was displayed on the yeast cell surface. Cell immunofluorescence is a more direct way to detect differentially produced proteins that are displayed on the yeast cell surface. The fluorescence microscopy results show that both fluorescence corresponding to the yeast-derived scFv and fluorescence corresponding to the E. coli-derived scFv can exist on the cell surface of same yeast cell. This confirms that the E. coli-derived scFv protein was successfully displayed on the yeast cell surface.

CONCLUSIONS

This method provides a rapid, simple, and high-efficiency strategy to increase the level of displayed protein on the yeast cell surface. Application of this technique may allow the yeast surface display system to be used to generate potential oral vaccines.

Yeast Surface Display of Two Proteins Previously Shown to Be Protective Against White Spot Syndrome Virus (WSSV) in Shrimp

Cell surface display using the yeasts Saccharomyces cerevisiae and Pichia pastoris has been extensively developed for application in bioindustrial processes. Due to the rigid structure of their cell walls, a number of proteins have been successfully displayed on their cell surfaces. It was previously reported that the viral binding protein Rab7 from the giant tiger shrimp Penaeus monodon (PmRab7) and its binding partner envelope protein VP28 of white spot syndrome virus (WSSV) could independently protect shrimp against WSSV infection. Thus, we aimed to display these two proteins independently on the cell surfaces of 2 yeast clones with the ultimate goal of using a mixture of the two clones as an orally deliverable, antiviral agent to protect shrimp against WSSV infection. PmRab7 and VP28 were modified by N-terminal tagging to the C-terminal half of S. cerevisiae α-agglutinin. DNA fragments, harboring fused-gene expression cassettes under control of an alcohol oxidase I (AOX1) promoter were constructed and used to transform the yeast cells. Immunofluorescence microscopy with antibodies specific to both proteins demonstrated that mutated PmRab7 (mPmRab7) and partial VP28 (pVP28) were localized on the cell surfaces of the respective clones, and fluorescence intensity for each was significantly higher than that of control cells by flow cytometry. Enzyme-linked immunosorbant assay (ELISA) using cells displaying mPmRab7 or pVP28 revealed that the binding of specific antibodies for each was dose-dependent, and could be saturated. In addition, the binding of mPmRab7-expressing cells with free VP28, and vice versa was dose dependent. Binding between the two surface-expressed proteins was confirmed by an assay showing agglutination between cells expressing complementary mPmRab7 and pVP28. In summary, our genetically engineered P. pastoris can display biologically active mPmRab7 and pVP28 and is now ready for evaluation of efficacy in protecting shrimp against WSSV by oral administration.

Immunomodulation of Fungal β-Glucan in Host Defense Signaling by Dectin-1

During the course of evolution, animals encountered the harmful effects of fungi, which are strong pathogens. Therefore, they have developed powerful mechanisms to protect themselves against these fungal invaders. β-Glucans are glucose polymers of a linear β(1,3)-glucan backbone with β(1,6)-linked side chains. The immunostimulatory and antitumor activities of β-glucans have been reported; however, their mechanisms have only begun to be elucidated. Fungal and particulate β-glucans, despite their large size, can be taken up by the M cells of Peyer's patches, and interact with macrophages or dendritic cells (DCs) and activate systemic immune responses to overcome the fungal infection. The sampled β-glucans function as pathogen-associated molecular patterns (PAMPs) and are recognized by pattern recognition receptors (PRRs) on innate immune cells. Dectin-1 receptor systems have been incorporated as the PRRs of β-glucans in the innate immune cells of higher animal systems, which function on the front line against fungal infection, and have been exploited in cancer treatments to enhance systemic immune function. Dectin-1 on macrophages and DCs performs dual functions: internalization of β-glucan-containing particles and transmittance of its signals into the nucleus. This review will depict in detail how the physicochemical nature of β-glucan contributes to its immunostimulating effect in hosts and the potential uses of β-glucan by elucidating the dectin-1 signal transduction pathway. The elucidation of β-glucan and its signaling pathway will undoubtedly open a new research area on its potential therapeutic applications, including as immunostimulants for antifungal and anti-cancer regimens.

Display of Eimeria tenella EtMic2 protein on the surface of Saccharomyces cerevisiae as a potential oral vaccine against chicken coccidiosis

S. cerevisiae is generally regarded as safe and benign organism and its surface display system may be used as a unique eukaryotic expression system that is suitable for expressing eukaryotic antigen. In addition to the convenience of vaccine delivery, the yeast cell wall has been shown to enhance the innate immunity when immunized with the yeast live oral vaccine. In the present study, we expressed the chicken coccidian E. tenella EtMic2, a microneme protein, on the surface of the S. cerevisiae and evaluated it as a potential oral vaccine for chicken against E. tenella challenge. The protective efficacy against a homologous challenge was evaluated by body weight gains, lesion scores and fecal oocyst shedding. The results showed that the live oral vaccine can improve weight gains, reduced cecal pathology and lower oocyst fecal shedding compared with non immunized controls. In addition, the yeast oral vaccine could stimulate humoral as well as cell mediate immune responses. These results suggested that EtMic2 displayed on the cell surface of S. cerevisiae could be used as potential live vaccine against chicken coccidiosis.

Surface display and bioactivity of Bombyx mori acetylcholinesterase on Pichia pastoris

A Pichia pastoris (P. pastoris) cell surface display system of Bombyx mori acetylcholinesterase (BmAChE) was constructed and its bioactivity was studied. The modified Bombyx mori acetylcholinesterase gene (bmace) was fused with the anchor protein (AGα1) from Saccharomyces cerevisiae and transformed into P. pastoris strain GS115. The recombinant strain harboring the fusion gene bmace-AGα1 was induced to display BmAChE on the P. pastoris cell surface. Fluorescence microscopy and flow cytometry assays revealed that the BmAChE was successfully displayed on the cell surface of P. pastoris GS115. The enzyme activity of the displayed BmAChE was detected by the Ellman method at 787.7 U/g (wet cell weight). In addition, bioactivity of the displayed BmAChE was verified by inhibition tests conducted with eserine, and with carbamate and organophosphorus pesticides. The displayed BmAChE had an IC50 of 4.17×10(-8) M and was highly sensitive to eserine and five carbamate pesticides, as well as seven organophosphorus pesticides. Results suggest that the displayed BmAChE had good bioactivity.

In vitro and in vivo expression of virulence genes in Trueperella pyogenes based on a mouse model

Trueperella pyogenes is an important opportunistic pathogen causing a number of pyogenic infections in ruminants and other animals. This microorganism expresses several extracellular virulence proteins that contribute to its pathogenic potential. To investigate the expression levels of haemolytic exotoxin pyolysin, neuraminidases, collagen-binding protein and fimbriae of T. pyogenes in routine culture and infection process, 10 T. pyogenes isolates which simultaneously harbored ftsY, plo, cbpA, fimA, fimC, nanP, and nanH genes were injected into 10/group Kunming (KM) mice to determine their virulence. In vitro expressions of these genes were determined by quantitative PCR. Subsequently, three typical isolates including an avirulent, a moderately virulent and a strongly virulent isolate were respectively injected into mouse model to determine the in vivo expression of these genes. Finally, significant correlation was observed between collagen-binding protein, neuraminidases, and fimbriae. The expression level of pyolysin was negatively correlated with the survival of injected mice. The time course of virulence gene expression was monitored based on the expression of virulence genes in mouse model. In conclusion, the in vitro and in vivo gene expression study showed a clear difference in virulence gene expression between virulent and non-virulent isolates.

Fermentation preparation of recombinant Vibrio anguillarum vaccine with heterogeneous antigen display

In the design of recombinant bacterial vector vaccine, heterogeneous antigen is displayed on the outer membrane of the vector strain to evoke polyvalent immunological protection. Thus, the expression of heterogeneous antigen in cells and its display on the outer membrane are of great concern for vaccine preparation. In our previous work, a multivalent bacterial vector vaccine MVAV6203A-1 was constructed by displaying the protective antigen GAPDH from Aeromonas hydrophila on the surface of an attenuated Vibrio anguillarum MVAV6203. In this work, a new fermentation medium was designed by a four-step method to improve the cell growth and antigen display of V. anguillarum MVAV6203A-1. First, suitable carbon and nitrogen sources were selected by a component swapping method. Second, the initial concentrations of carbon and nitrogen sources were determined by orthogonal design. Then three main factors to significantly affect cell growth and antigen expression were screened by a Plackett-Burman design. Finally, the three main factors were meticulously optimized by response surface methodology. Based on this medium, a fed-batch fermentation process was established in a 5-L bioreactor, and the dry cell weight, the antigen expression in cells, and its display on outer membrane reached 5.98 g/L, 2.82 mg/g DCW, and 0.119 mg/g DCW, respectively.

Protection of Penaeus monodon against white spot syndrome virus by inactivated vaccine with herbal immunostimulants

To improve the immune response in tiger shrimp Penaeus monodon against WSSV infection, juveniles (350 ± 10 mg) were vaccinated with formalin-inactivated WSSV and fed with herbal immunostimulants. The methanolic extracts of herbal immunostimulants such as Acalypha indica, Cynodon dactylon, Picrorrhiza kurrooa, Withania somnifera and Zingiber officinalis were incorporated in formulated diets at different concentrations; 250 (ED(1)), 500 (ED(2)), 1000 (ED(3)) and 2000 (ED(4)) mg kg(-1) of feed and fed for 60 days after vaccination. After 30 and 60 days intervals of feeding, the shrimps were challenged with WSSV, which were isolated and propagated from the infected crustaceans. The shrimps fed with control diets (C(1)) succumbed to death within 5 days after WSSV challenge, when no vaccination and immunostimulations were given. The other control groups (C(2) and C(3)) had slight improvements in all parameters including survival. The percentage survival was significantly (P < 0.05) increased to 30, 50 and 60% in the ED(2), ED(3) and ED(4) diets respectively after 60 days challenging. The better haematological, biochemical and immunological parameters were also found in the herbal extracts supplemented diets fed vaccinated shrimps. The present study revealed that the combined effect of immunostimulation and vaccination helped to boost the immune system against WSSV infection and hence this application can be adopted for shrimp culture.

Isomaltulose production via yeast surface display of sucrose isomerase from Enterobacter sp. FMB-1 on Saccharomyces cerevisiae

The gene encoding sucrose isomerase from Enterobacter sp. FMB-1 species (ESI) was displayed on the cell surface of Saccharomyces cerevisiae EBY100 using a glycosylphosphatidylinositol (GPI) anchor attachment signal sequence. Fluorescence activated cell sorting (FACS) analysis and immunofluorescence microscopy confirmed the localization of ESI on the yeast cell surface. The displayed ESI (dESI) was stable at a broad range of temperatures (35-55 °C) and pHs (pH 5-7) with optimal temperature and pH at 45 °C and pH 7.0, respectively. In addition, the thermostability of the dESI was significantly enhanced compared with the recombinant ESI expressed in Escherichia coli. Biotransformation of sucrose to isomaltulose was observed in various ranges of substrate concentrations (50-250 mM) with a 6.4-7.4% conversion yield. It suggested that the bioconversion of sucrose to isomaltulose can be successfully performed by the dESI on the surface of host S. cerevisiae.

Developments in high-yield system expressed vaccines and immunotherapy

Conventional vaccine production techniques are outdated, leaving the world defenseless to viruses and pathogens. Successful protection necessitates the innovation of strategies that can generate an induced defensive humoral and cellular response with: ease of mass production, nominal side-effects, and controlled design specificity, all while being cost effective. Fortunately, technology exists to facilitate such advances in this billion dollar industry and this review is focused on recent publications and patents which hold promise to revolutionize the fight against pathogenic illnesses.

In vitro and in vivo expression of virulence genes in Vibrio isolates belonging to the Harveyi clade in relation to their virulence towards gnotobiotic brine shrimp (Artemia franciscana)

Vibrios belonging to the Harveyi clade are pathogenic marine bacteria affecting both vertebrates and invertebrates, thereby causing a severe threat to the aquaculture industry. In this study, the expression of haemolysin, metalloprotease, serine protease, the quorum sensing master regulator LuxR and the virulence regulator ToxR in different Harveyi clade isolates was measured with reverse transcriptase real-time PCR with specific primers. There was relatively low variation in the in vitro expression levels of the quorum sensing master regulator luxR (sevenfold), whereas for the other genes, the difference in expression between the isolates showing lowest and highest expression levels was over 25-fold. Furthermore, there was a significant correlation between expression levels of toxR and luxR and between the expression levels of these regulators and the protease genes. The expression levels of luxR, toxR and haemolysin were negatively correlated with the survival of brine shrimp larvae challenged with the isolates. Finally, a non-virulent, a moderately virulent and a strongly virulent isolate were selected to study in vivo expression of the virulence genes during infection of gnotobiotic brine shrimp larvae. The in vivo gene expression study showed a clear difference in virulence gene expression between both virulent isolates and the non-virulent isolate.

Preparation of a whole-cell biocatalyst of Aspergillus niger lipase and its practical properties

Aspergillus niger lipase (ANL), a widely used hydrolase, was displayed for the first time on the surface of Saccharomyces cerevisiae using a-agglutinin as an anchor protein. Localization of ANL on the cell surface was confirmed by immunofluorescence microscopy. The displayed ANL was confirmed to be active toward tributyrin and p-nitrophenyl caprylate (pNPC). The hydrolytic activity toward pNPC reached 43.8 U/g of dry cell weight after induction by galactose for 72 h. The ANL-displaying cells were characterized for their use as whole-cell biocatalysts. The optimum temperature was 45 °C, and the pH was 7.0. The cells had good thermostability, retaining almost 80% of the full activity after incubation at 60 °C for 1 h, and >80% of the full activity at 50 °C for 6 h. The displayed lipase showed a preference for medium-chain fatty acid p-nitrophenyl esters. Therefore, the produced whole-cell catalyst is likely to have a wide range of applications.

Immunoproteomic analysis and identification of novel immunogenic proteins from Vibrio harveyi

AIMS

The main aim of this study was to screen novel immunogenic proteins of Vibrio harveyi, which could be vaccine candidates.

METHODS AND RESULTS

  Whole-cell proteins of V. harveyi, strain Li01 and Huang01, were first separated by isoelectric focusing, followed by 2D-PAGE, respectively. Immunogenic proteins were identified by Western blotting, using Epinephelus coioides antisera against V. harveyi strain Li01. Western blot analyses revealed 16 shared immunogenic protein spots in both strains. All of the immunogenic proteins were successfully identified and corresponded to 15 proteins. None of these proteins have been previously reported as immunogenic for V. harveyi. Of the 15 proteins, 11 are specific immunoreactive proteins and four are nonspecific immunoreactive proteins. Furthermore, outer membrane protein N (spot 2) and oligopeptide ATP-binding cassette (ABC) transporter (spot 3) were used as immunogens to immunize E. coioides for investigation of their protective abilities and activities. The E. coioides immunized with OmpN has abilities to fight against infections caused by V. harveyi Li01 and Huang01. However, vaccination with oligopeptide ABC transporter induces low protective immune response in fish.

CONCLUSIONS

  Eleven novel specific antigens were found, and OmpN could potentially be used as vaccine candidate for the development of novel vaccine against V. harveyi.

SIGNIFICANCE AND IMPACT OF THE STUDY

These data show that immunoproteomics methods can be successfully applied in identifying immunogenic proteins of V. harveyi, which helps to search for the protective antigens in future.

beta-1,3-glucanase inhibits activity of the killer toxin produced by the marine-derived yeast Williopsis saturnus WC91-2

The marine-derived Williopsis saturnus WC91-2 was found to produce very high killer toxin activity against the pathogenic yeast Metschnikowia bicuspidata WCY isolated from the diseased crab. It is interesting to observe that the purified beta-1,3-glucanase from W. saturnus WC91-2 had no killer toxin activity but could inhibit activity of the WC91-2 toxin produced by the same yeast. In contrast, the WC91-2 toxin produced had no beta-1,3-glucanase activity. We found that the mechanisms of the inhibition may be that the beta-1,3-glucanase competed for binding to beta-1,3-glucan on the sensitive yeast cell wall with the WC91-2 toxin, causing decrease in the amount of the WC91-2 toxin bound to beta-1,3-glucan on the sensitive yeast cell wall and the activity of the WC91-2 toxin against the sensitive yeast cells. In order to make W. saturnus WC91-2 produce high activity of the WC91-2 toxin against the yeast disease in crab, it is necessary to delete the gene encoding beta-1,3-glucanase.

Application of the yeast-surface-display system for orally administered salmon calcitonin and safety assessment

High manufacturing costs and oral delivery are the constraints in clinical application of calcitonin. We selected surface-displayed Saccharomyces cerevisiae as a low-cost and safe carrier for oral delivery of salmon calcitonin (sCT). The sCT DNA fragment, optimized according to the codon preference of S. cerevisiae, was synthesized and cloned into the plasmid M-pYD1 to yield recombinant yAGA2-sCT, which was induced to express sCT by galactose for 0, 12, and 24 h. sCT expression was detected on the cell surface by indirect immunofluorescence and peaked at 12 h. About 65% recombinants expressed sCT on flow cytometry. The in vivo and in vitro activity of recombinant sCT was determined by detecting bioactivity of antiosteoclastic absorption on bone wafers and orally administering yAGA2-sCT to Wistar rats, respectively. For safety assessment of yAGA2-sCT, we observed abnormalities, morbidity, and mortality and determined body weight, serum chemistry parameters, hematological parameters, and organ weight. In vitro bioactivity of the recombinant sCT was similar to that of commercial sCT, Miacalcic; oral administration of 5 g/kg yAGA2-sCT induced a long-term hypocalcemic effect in Wistar rats and no adverse effects. This study demonstrates that yAGA2-sCT anchoring sCT protein on a S. cerevisiae surface has potential for low-cost and safe oral delivery of sCT.

Genetic modification of the marine-derived yeast Yarrowia lipolytica with high-protein content using a GPI-anchor-fusion expression system

Yarrowia lipolytica SWJ-1b isolated from the marine fish gut was found to contain 47.6 g of crude protein per 100 g of cell dry weight and had potential use as single cell protein. When the gene encoding enhanced green fluorescent protein (EGFP) was inserted into the surface display plasmid pINA1317-YlCWP110 and expressed in uracil mutant of Y. lipolytica SWJ-1b, the corresponding protein was successfully displayed on the cell surface, and 100% of the yeast cells exhibited the anchored target proteins. We found that yeast cells displaying EGFP were similar to those of Y. lipolytica SWJ-1b. Furthermore, C(18:1) and C(18:3) fatty acids biosynthesis in the marine yeast cells displaying the heterologous EGFP was weakly enhanced compared with that in its wild-type. The results suggest that the marine-derived Y. lipolytica SWJ-1b can be armed with the heterologous protein by the genetic modification and further used as single cell protein.

Evaluation of the vaccine potential of a cytotoxic protease and a protective immunogen from a pathogenic Vibrio harveyi strain

Vibrio harveyi is an important aquaculture pathogen that can infect a number of fish species and marine invertebrates. A putative protease, Vhp1, was identified from a pathogenic V. harveyi strain isolated from diseased fish as a protein with secretion capacity. Vhp1 is 530 amino acids in length and shares high sequence identities with several extracellular serine proteases of the Vibrio species. In silico analysis identified a protease domain in Vhp1, which is preceded by a subtilisin-N domain and followed by a bacterial pre-peptidase C-terminal domain. Purified recombinant protein corresponding to the protease domain of Vhp1 exhibited apparent proteolytic activity that was relatively heat-stable and reached maximum at pH 8.0 and 50 degrees C. The activity of purified recombinant Vhp1 protease was enhanced by Ca(2+) and inhibited by Mn(2+) and ethylenedinitrilotetraacetic acid. Cytotoxicity analyses indicated that recombinant Vhp1 protease was toxic to cultured Japanese flounder cells and could cause complete cell lysis. Immunoprotective analysis using Japanese flounder as an animal model showed that purified recombinant Vhp1 in the form of a denatured and proteolytically inactive protein was an effective subunit vaccine. To improve the vaccine potential of Vhp1, an Escherichia coli strain that expresses and secrets a cytotoxically impaired Vhp1 was constructed, which, when used as a live vaccine, afforded a high level of protection upon the vaccinated fish against lethal V. harveyi challenge. Taken together, these results demonstrate that Vhp1 is a cytotoxic protease and an effective vaccine candidate against V. harveyi infection.

Identification and immunoprotective analysis of an in vivo-induced Edwardsiella tarda antigen

Edwardsiella tarda is a severe aquaculture pathogen that can infect many important fish species cultured worldwide. The aim of this study was to evaluate the vaccine potential of an E. tarda antigen, Eta21, which was identified from a pathogenic E. tarda strain via the method of in vivo-induced antigen technology (IVIAT). Eta21 is 510-amino acid in length and shares approximately 58% sequence identity with a putative peptidase of several bacterial species. eta21 was subcloned into Escherichia coli, and recombinant Eta21 was purified as a histidine-tagged protein. When used as a subunit vaccine, purified recombinant Eta21 was effective against lethal E. tarda challenge in a Japanese flounder model. In order to improve the immunoprotective efficacy of Eta21, the chimera AgaV-Eta21 was constructed, which consists of Eta21 fused in-frame to the secretion domain of AgaV, an extracellular beta-agarase. E. coli DH5alpha harboring plasmid pTAET21, which constitutively expresses agaV-eta21, was able to produce and secret AgaV-Eta21 into the extracellular milieu. Vaccination of Japanese flounder with live DH5alpha/pTAET21 elicited immunoprotection that is significantly higher in level than that induced by vaccination with purified recombinant Eta21. Vaccination with DH5alpha/pTAET21 and recombinant Eta21 both induced the production of specific serum antibodies at four to eight weeks post-vaccination. Taken together, these results demonstrate that Eta21, especially that delivered by DH5alpha/pTAET21, is an effective vaccine candidate against E. tarda infection.

The surface display of the alginate lyase on the cells of Yarrowia lipolytica for hydrolysis of alginate

The alginate lyase structural gene (AlyVI gene) was amplified from plasmid pET24-ALYVI carrying the alginate lyase gene from the marine bacterium Vibrio sp. QY101 which is a pathogen of Laminaria sp. When the gene was cloned into the multiple cloning site of the surface display vector pINA1317-YlCWP110 and expressed in cells of Yarrowia lipolytica, the cells displaying the alginate lyase could form clear zone on the plate containing sodium alginate, indicating that they had high alginate lyase activity. The cells displaying alginate lyase can be used to hydrolyze poly-beta-D: -mannuronate (M) and poly-alpha-L: -guluronate (G) and sodium alginate to produce different lengths of oligosaccharides (more than pentasaccharides). This is the first report that the yeast cells displaying alginate lyase were used to produce different lengths of oligosaccharides from alginate.

Identification of Vibrio harveyi isolated from diseased Asian seabass Lates calcarifer by use of 16S ribosomal DNA sequencing

The grow out of Asian seabass Lates calcarifer in marine net-cages is a popular aquaculture activity in Malaysia. Production of this species is greatly affected by the occurrence of vibriosis, which causes heavy mortality. Generally, young fish are more susceptible; they exhibit anorexia and skin darkening, followed by heavy mortality. The acutely affected older fish may also exhibit bloody lesions around the anus and the base of the fins. Twenty-one bacterial isolates obtained from internal organs (kidney, heart, spleen and liver) of the affected specimens were subjected to phenotypic characterization, testing for antibiotic susceptibility, and 16S ribosomal DNA sequencing. The sequencing result showed that all of the bacterial isolates belonged to Vibrio harveyi. The phenotypic characterization, however, identified 4 of the bacterial isolates as V. harveyi, 16 as V. parahaemolyticus, and 1 as V. alginolyticus. These findings suggest that biochemical features alone cannot be reliably used to identify bacterial pathogens, including V. harveyi, in aquaculture. Antibiotic susceptibility assays showed that some antibiotics, including oxytetracycline, nitrofurantoin, furazolidone, streptomycin, sulfamethoxazole, chloramphenicol, nalidixic acid, and oxolinic acid were effective against V. harveyi. Considering the side effects of these antibiotics, however, their use is not recommended in the aquaculture of Asian seabass.

Alkaline protease gene cloning from the marine yeast Aureobasidium pullulans HN2-3 and the protease surface display on Yarrowia lipolytica for bioactive peptide production

The alkaline protease genes (cDNAALP2 gene and ALP2 gene) were amplified from complementary DNA (cDNA) and genomic DNA of the marine yeast Aureobasidium pullulans HN2-3, respectively. An open reading frame of 1,248 bp encoding a 415-amino acid protein with a calculated molecular weight of 42.9 kDa was characterized. The ALP2 gene contained two introns, which had 54 and 52 bp, respectively. When the cDNAALP2 gene was cloned into the multiple cloning sites of the surface display vector pINA1317-YlCWP110 and expressed in cells of Yarrowia lipolytica, the cells displaying protease could form a clear zone on the double plate containing milk protein and had protease activity. The cells displaying alkaline protease were also found to be able to produce bioactive peptides from different sources of proteins. The peptides produced from single-cell protein of marine yeast strain G7a had the highest angiotensin-converting enzyme inhibitory activity, while the peptides produced from spirulina protein had the highest antioxidant activity. This is the first report that the yeast cells displaying alkaline protease were used to produce bioactive peptides.

An outer membrane protein, OmpK, is an effective vaccine candidate for Vibrio harveyi in Orange-spotted grouper (Epinephelus coioides)

The outer membrane proteins of the fish pathogen, Vibrio harveyi, have a role in interaction between bacterium and host and are potential candidates for vaccine development. In this study, the gene encoding an outer membrane protein, OmpK, which serves as the receptor for broad-host-range vibriophage KVP40 in V. harveyi, was isolated and characterized. Then the OmpK gene coding for mature peptide was subcloned into prokaryotic expression vector pBV220 and transformed into Escherichia coli DH5 alpha strain. After temperature induction, a recombinant protein was detected about 28 kDa in molecular weight and accounted for 24.8% of total proteins of whole cell as estimated by SDS-PAGE and scanning analysis of gel image. Polyclonal antibodies were raised in rabbits against the purified protein and the reaction of the antibody was confirmed by western blotting using the purified protein and crude extract of V. harveyi. Orange-spotted groupers (Epinephelus coioides) vaccinated with recombinant OmpK produced specific antibodies, and were highly resistant to infection by virulent V. harveyi. These results indicate that the OmpK is an effective vaccine candidate against V. harveyi in Orange-spotted groupers.

Subcellular components of Vibrio harveyi and probiotics induce immune responses in rainbow trout, Oncorhynchus mykiss (Walbaum), against V. harveyi

Bacterial subcellular components and probiotics were successful for the stimulation of immunity and the prevention of Vibrio harveyi infections in rainbow trout, Oncorhynchus mykiss (Walbaum). Rainbow trout were immunized with whole inactivated cells of V. harveyi to obtain polyclonal antibodies against specific antigens. Western blotting showed a unique reactive band (approximately 93 kDa) between serum and bacterial proteins from outer membrane proteins (OMP) and extracellular products (ECP). Probiotics were selected according to their capability to inhibit V. harveyi. Two of these bacteria, i.e. A3-47 and A3-51, showed cross-reactivity with V. harveyi antiserum. Their OMPs and ECPs were reactive with V. harveyi antiserum in bands of approximately 93 kDa for A3-51 and higher for A3-47. In vivo tests determined that fish fed with A3-51 produced cross-reactive antibodies against V. harveyi and also, the survival of these fish infected with V. harveyi was high, being similar to the level achieved with vaccinated fish. Thus, the probiotics, when administered as live preparations, were capable of producing cross-reactive antibody against specific bacterial pathogens.

Novel bacterial surface display systems based on outer membrane anchoring elements from the marine bacterium Vibrio anguillarum

Surface display of heterologous peptides and proteins such as receptors, antigens, and enzymes on live bacterial cells is of considerable value for various biotechnological and industrial applications. In this study, a series of novel cell surface display systems were examined by using Vibrio anguillarum outer membrane protein and outer membrane lipoprotein as anchoring motifs. These display systems consist of (i) the signal sequence and first 11 N-terminal amino acids of V. anguillarum outer membrane lipoprotein Wza, or the signal sequence and first 9 N-terminal amino acids of the mature major Escherichia coli lipoprotein Lpp, and (ii) transmembrane domains of V. anguillarum outer membrane proteins Omporf1, OmpU, or Omp26La. In order to assay the translocation efficiency of constructed display systems in bacteria, green fluorescent protein (GFP) was inserted to the systems and the results of GFP surface localization confirmed that four of the six surface display systems could successfully display GFP on the E. coli surface. For assaying its potential application in live bacteria carrier vaccines, an excellent display system Wza-Omporf1 was fused with the major capsid protein (MCP) of large yellow croaker iridovirus and introduced into attenuated V. anguillarum strain MVAV6203, and subsequent analysis of MCP surface localization proved that the novel display system Wza-Omporf1 could function as a strong tool in V. anguillarum carrier vaccine development.

Yeast surface display for protein engineering and characterization

Yeast surface display is being employed to engineer desirable properties into proteins for a broad variety of applications. Labeling with soluble ligands enables rapid and quantitative analysis of yeast-displayed libraries by flow cytometry, while cell-surface selections allow screening of libraries with insoluble or even as-yet-uncharacterized binding targets. In parallel, the utilization of yeast surface display for protein characterization, including in particular the mapping of functional epitopes mediating protein–protein interactions, represents a significant recent advance.