747 research outputs found

    Phenotypic variation in Vibrio harveyi : virulence factors and immune response in Artemia franciscana

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    Phenotypic (phase) variation or phenotypic switching is defined as a process of reversible, high frequency phenotypic variation. Until now, little is known about phenotypic variation in Vibrio especially in luminous vibriosis diseases for many aquaculture species. Vibrio harveyi, a luminescent Gram-negative motile marine bacterium, is an important pathogen responsible for causing severe diseases in shrimp, finfish and molluscs leading to severe economic losses. The present study showed that switching from the luminescent (L) to the non-luminescent (NL) state changed the phenotypic physiology or behavior of V. harveyi. Subsequently, gnotobiotic Artemia model organism (GART) system was used to investigate the influence of virulent and non-virulent L and NL of the wild type V. harveyi and its quorum sensing (QS) mutant on immune defense of A. franciscana. Next, the full-length sequence of Hmgb1 of A. franciscana was isolated for the first time in this thesis. In conclusion, this study indicates that in vitro virulence factors are changed as a result of phenotypic variation in V. harveyi. These alterations in the L and NL variants of the wild type BB120 and its QS mutan

    Investigation of enzymatic hydrolysis process to valorize waste mussel shells

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    Blue mussels (Mytilus edulis) are the most common mussel harvested with high value nutritional compounds including proteins, vitamins ( C, A, and B12), and minerals (iron and calcium). Blue mussels are filter feeders eating plankton from the water. Mussel farming is more sustainable form of aquaculture as fish meal, chemicals (antibiotics and additives) are not required and the risk of pathogens escaping into the coastal ecosystems is minimal. The worldwide aquaculture and processing of mussels is rapidly increasing and blue mussels are Canada’s top shellfish aquaculture product produced in every province in Atlantic Canada, as well as in Quebec and British Columbia. By-products from mussel aquaculture and processing, such as processed mussel shells, unmarketable and broken mussels, make up a significant waste stream from this industry and are currently difficult to valorize. Waste mussel shells are a potential source of bio-calcium carbonate and proteins. Protein enzymatic hydrolysis, a process where protein macromolecules are hydrolyzed to amino acids and peptides of smaller size. The process is a simple, effective, and environmentally friendly means of valorizing waste mussel shells, producing two product streams: mussel shells without residual meat and non-toxic hydrolysate. This study includes a review of literature on valorizations of waste mussel shells for the source of bio-calcium carbonate and proteins. The review shows the lack of kinetic studies for enzymatic hydrolysis of mussels, required for any scale up to a commercial process. In this study, mussel meat is removed from whole mussels by using enzymatic hydrolysis technology. The process is carried out using a food grade enzyme, Multifect PR 6L, and tap water at neutral pH, with no pH control, and a temperature 50゚C. To determine the rate of hydrolysis, the degree of digested meat (DM) is used in this study instead of the degree of hydrolysis (DH). The enzyme and substrate concentrations were varied to determine the impact of these factors on the final digested meat and rate of reaction. The fraction of digested meat (or degree of shell cleaning) varied from 0.57 g/gₘₑₐₜ to 0.94 g/gₘₑₐₜ depending on the enzyme and substrate (meat) concentrations. Soluble protein concentration of the obtained hydrolysates was also analyzed. After evaluating a number of reaction rate mechanisms, the first-order model is suggested as the best model to describe the enzymatic hydrolysis of whole raw mussels. The soluble protein concentration in the resulting hydrolysate increases with the increases in the amount of digested meat

    Characterization of phenotype variations of luminescent and non-luminescent variants of Vibrio harveyi wild type and quorum sensing mutants

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    Vibrio harveyi, a luminescent Gram-negative motile marine bacterium, is an important pathogen responsible for causing severe diseases in shrimp, finfish and molluscs leading to severe economic losses. Non-luminescent V.harveyi obtained by culturing luminescent strains under static and dark condition were reported to alter the levels of virulence factors and metalloprotease gene and luxR expression when compared to their luminescent variants. Presently, we conducted an in vitro study aiming at the characterization of virulence-related phenotypic traits of the wild-type V.harveyi BB120 strain and its isogenic quorum sensing mutants before and after switching to the non-luminescent status. We measured the production of caseinase, haemolysin and elastase and examined swimming motility and biofilm formation. Our results showed that switching from the bioluminescent to the non-luminescent state changed the phenotypic physiology or behaviour of V.harveyi resulting in alterations in caseinase and haemolytic activities, swimming motility and biofilm formation. The switching capacity was to a large extent independent from the quorum sensing status, in that quorum sensing mutants were equally capable of making the phenotypic switch

    Labor and Its Efficiency in Equitized State-owned Enterprises in Vietnam

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    This study is conducted for evaluating changes in labor efficiency of state-owned enterprises after equitization. Data were collected from audited financial statements and reports of labor and average income in 138 state owned enterprises after equitization. After calculating labor efficiency according to revenue and earnings of enterprises in the sample, we apply the comparative method for labor, average income and labor efficiency before and after equitization. Then, we use the Wilcoxon Signed-Rank Test to compare the fluctuation in the ratios between two years after equitization with one year prior to equitization. The results show that after equitization, enterprises achieve an increase in average number of labor, improved average labor income and enhanced labor efficiency. Keywords: Equitization, state-owned firm, labor efficiency, Vietnam. DOI: 10.7176/RJFA/10-5-10 Publication date:March 31st 201

    Complex Monge-Amp\`ere equations for plurifinely plurisubharmonic functions

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    This paper studies the complex Monge-Amp\`ere equations for F\mathcal F-plurisubharmonic functions in bounded F\mathcal F-hyperconvex domains. We give sufficient conditions for this equation to solve for measures with a singular part

    The Combined Use of Pediococcus pentosaceus and Fructooligosaccharide Improves Growth Performance, Immune Response, and Resistance of Whiteleg Shrimp Litopenaeus vannamei Against Vibrio parahaemolyticus

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    In this study, we evaluated the effect of probiotic bacteria Pediococcus pentosaceus supplemented at different inclusion levels in a control diet [basal diet containing 0.5% fructooligosaccharide (FOS)] on the growth performance, feed conversion ratio, immune response, and the disease resistance of whiteleg shrimp Litopenaeus vannamei juveniles against Vibrio parahaemolyticus. A control diet with 0.5% FOS but without P. pentosaceus supplementation (Control) was prepared. In addition, three other test diets were also formulated: control diet supplemented with P. pentosaceus at (i) 1 x 10(6) cfu g(-1) diet (P1), (ii) 1 x 10(7) cfu g(-1) diet (P2), or (iii) 1 x 10(8) cfu g(-1) diet (P3). After a 60-day feeding trial, the experimental shrimps were challenged with V. parahaemolyticus. The results showed that dietary supplementation of P. pentosaceus significantly improved the growth performance and immune responses of L. vannamei juveniles. The juveniles that were fed with a P2 or P3 diet recorded the maximum increase in the final body weight, final length, weight gain, and survival rate. The total hemocyte counts, phenoloxidase, and lysozyme activity of shrimp fed with either of these two diets were significantly enhanced. The results also showed that juveniles fed with a P2 or P3 diet exhibited significantly lower mortality when challenged with V. parahaemolyticus. Overall results suggested that a combination of P. pentosaceus at the inclusion level of 1 x 10(7) cfu g(-1) diet (P2) and 0.5% FOS could be considered as a potential synbiotic formulation for improving the growth, health, and robustness of L. vannamei

    The Efficiency and the Performance of the Logistics Global Supply Chain Activities to Vietnam Exportation: an Empirical Case Study

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    Purpose: This research paper aims to determine the factors affecting the efficiency and logistics performance index (LPI) of Vietnam's exports to foreign partners during 2018-2022 are due to the impact of the COVID-19 pandemic.   Theoretical Framework: Based on the primary factors affecting the efficiency and performance of global supply chain activities in logistics for Vietnam's exports, including practical impact and logistics results of enterprises in Vietnam. Based on the primary factors affecting the efficiency and performance of global supply chain activities in logistics for Vietnam's exports, including (1). Customs efficiency (speed, simplicity and predictability of customs clearance procedures) (2). Quality of infrastructure related to trade and transport, including Roads, railways, ports, airports, warehouses and information technology ...(3). The level of ease when arranging to transport import and export goods with competitive prices (costs such as warehousing fees, port fees, tolls ... ) (4). Capacity and quality of logistics service providers ... (5). Ability to track and trace shipments. (6). Timeliness of the shipment to the destination within the specified time limit. The practical impact and logistics results of enterprises in Vietnam.   Method: The panel approach allows the authors to explore the heterogeneity in data across countries. Fixed effects (FE) and random effects (RE) models were used to estimate the model. Then, the Hausman test is carried out to decide which model is appropriate. The data were collected from 240 observations from Vietnam and 80 major export partner countries of Vietnam.   Findings: The research results show that the cost, time and capacity of providing logistics services have the most significant impact on Vietnam's exports.   Practical & social implications: Overall, to increase the efficiency and logistics efficiency of enterprises. The Vietnamese Government needs to cooperate and propose ideas to partner countries to improve logistics activities for exports from Vietnam. Logistics is beginning to play an increasingly important role in the competitiveness of economies.   Originality values: This study also confirms the sustainability of the extended gravity model using OLS and RE methods by substituting different variables for the country's logistics efficiency and solving the endogenous problem in the model while applying the regression method to industrial variables. We find that an 1% improvement in Vietnam's logistics would increase Vietnam's exports by 1.443%, and an 1% improvement in a partner country’s performance would help promote Vietnam's exports to this country by 0.546%

    Simple thermal-electrical model of photovoltaic panels with cooler-integrated sun tracker

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    This paper presents a simple thermal-electrical model of a photovoltaic panel with a cooler-integrated sun tracker. Based on the model and obtained weather data, we analyzed the improved overall efficiency in a year as well as the performance in each typical weather case for photovoltaic panels with fixed-tilt systems with a tilt angle equal to latitude, fixed-tilt systems with cooler, a single-axis sun tracker, and a cooler-integrated single-axis sun tracker. The results show that on a sunny summer day with few clouds, the performance of the photovoltaic panels with the proposed system improved and reached 32.76% compared with the fixed-tilt systems. On a sunny day with clouds in the wet, rainy season, because of the low air temperature and the high wind speed, the photovoltaic panel temperature was lower than the cooler’s initial set temperature; the performance of the photovoltaic panel with the proposed system improved by 12.55% compared with the fixed-tilt system. Simulation results show that, over one year, the overall efficiency of the proposed system markedly improved by 16.35, 13.03, and 3.68% compared with the photovoltaic panel with the fixed-tilt system, the cooler, and the single-axis sun tracker, respectively. The simulation results can serve as a premise for future experimental models