Optimization of bioinsecticides overproduction by Bacillus thuringiensis subsp. kurstaki using linear regression

A multiple linear regression analyses were performed to screen for the significant factors simultaneously influencing production of delta-endotoxin, proteolytic activities and spore formation by a Bacillus thuringiensis kurstaki strain. Investigated factors included: pH of the medium, available oxygen and inoculum size. It was observed that oxygen availability was the most influencing setting on both delta-endotoxins production and spores counts, followed by initial pH of the medium and inoculum size. On other hand, pH of medium was found to be the most significant parameter for proteolytic activity, followed by inoculum size and dissolved oxygen. Our results suggested that the first order with two-factor interaction model seemed to be more satisfactory than simple first order model for optimization of delta-endotoxin overproduction. The coefficients of determination (R2) indicated a better adequacy of the second order models to justify the obtained data. Based on results, relationships between delta-endotoxins production, proteolytic activities and spores counts were established. Our results can help to balance delta-endotoxins production and its stability.Scopu

Experimental design and Bayesian networks for enhancement of delta-endotoxin production by Bacillus thuringiensis

Bacillus thuringiensis (Bt) is a Gram-positive bacterium. The entomopathogenic activity of Bt is related to the existence of the crystal consisting of protoxins, also called delta-endotoxins. In order to optimize and explain the production of delta-endotoxins of Bacillus thuringiensis kurstaki, we studied seven medium components: soybean meal, starch, KH2PO4, K2HPO4, FeSO4, MnSO4, and MgSO4 and their relationships with the concentration of delta-endotoxins using an experimental design (Plackett—Burman design) and Bayesian networks modelling. The effects of the ingredients of the culture medium on delta-endotoxins production were estimated. The developed model showed that different medium components are important for the Bacillus thuringiensis fermentation. The most important factors influenced the production of delta-endotoxins are FeSO4, K2HPO4, starch and soybean meal. Indeed, it was found that soybean meal, K2HPO4, KH2PO4 and starch also showed positive effect on the delta-endotoxins production. However, FeSO4 and MnSO4 expressed opposite effect. The developed model, based on Bayesian techniques, can automatically learn emerging models in data to serve in the prediction of delta-endotoxins concentrations. The constructed model in the present study implies that experimental design (Plackett—Burman design) joined with Bayesian networks method could be used for identification of effect variables on delta-endotoxins variation

Statistical Analysis of Cultural Parameters Influencing Delta-Endotoxins and Proteases Productions by Bacillus thuringiensis kurstaki

Bacillus thuringiensis is a spore-forming bacterium that produces delta-endotoxins, which are toxic to lepidopterans, dipterans and coleopterans. Concomitantly with production of delta-endotoxins, B. thuringiensis produces proteolytic enzymes during growth and sporulation, affecting yields of toxins production. In this work, an experimental factorial design was employed for the dual evaluation of effects of delta-endotoxins and proteolytic enzyme on activity of a B. thuringiensis subsp. kurstaki strain. Main effects and interactions of three factors (soybean meal, starch and aeration) under two conditions (0 and 7 g/l NaCl) were analysed using statistical techniques. Regression models, known as useful tool to build relationships between variables and subsequently to make predictions, were suggested to fit the experimental data. Yields ranged between 6.10–15.76 × 10−7 μg and 18.18–30.30 × 10−7 IU for delta-endotoxin and proteolytic enzymes per cell, respectively. When NaCl (7 g/l) was added to the medium, yields ranged from 15.51 to 38.06 for delta-endotoxins and from 9.56 to 48.73 for proteases. Starch, soybean meal and aeration improved the delta-endotoxins production. Interactions (starch × air) and (soybean meal × air) showed a negative effect on delta-endotoxin yield, while (starch × soybean meal) had no effect. The active function of aeration was enhanced when NaCl (7 g/l) was added, and effects of all interactions on delta-endotoxins yield had been nullified. Soybean meal and aeration had negative effects on proteolytic activity, in contrast to starch, (starch × air) and (soybean × air), which improved proteolytic activity yields. The inhibitory role of soybean meal shifted to positive effect according to the presence of NaCl (7 g/l) in the culture medium.Scopu

Nutritional Requirements to Improve Delta-Endotoxins Production of Bacillus thuringiensis var. kurstaki Using Mixed Designs Modelling

Bacillus thuringiensiskurstaki is a soil bacterium that produces insecticidal toxins called delta-endotoxins. In order to increase the toxic crystal concentrations in a low-cost culture medium and thus improve the biopesticide quality to control insect pests, the Plackett Burman screening method was applied. It was shown a tool to evaluate the significance of the selected seven factors (KH2PO4, K2HPO4, MgSO4, MnSO4, FeSO4, soybean meal, starch) which are necessary to the production of the delta-endotoxins. This was performed into two different shake flasks (250 and 500 ml). The main factors that affected the production of delta-endotoxins are shown to be soybean meal, starch, and FeSO4 in 250 ml culture flasks. In 500 ml culture flasks, soybean meal and FeSO4 are the principal factors influencing the delta-endotoxin production. The multiple linear regression, a method applied as the merging dataset of the two Plackett Burman designs, established that soybean meal and starch are the factors positively affecting the production of delta-endotoxins, in contrast to FeSO4. Furthermore, the available oxygen in culture flasks showed no significant negative effect on delta-endotoxin production. This study revealed that mixed method designs were useful to identify the significance and the effect of hidden culture parameters.Scopu

A Bioinformatic Study on the Potential Anti-Vitiligo Activity of a <i>Carpobrotus edulis</i> Compound

The plant Carpobrotus edulis has traditionally been known for its wide applications in diseases, especially vitiligo, which is characterized by patches and white macules caused by the loss of melanocytes. One of the chemical treatments for vitiligo consists mainly of skin repigmentation and usually leads to a non-durable effect by inhibiting the Janus kinase (JAK) signal transduction (STAT pathway). JAK inhibitors generally block multiple JAK tyrosine kinases, which leads to secondary effects. In this study, natural molecules from Carpobrotus edulis were extracted and tested using a structure-based drug-design approach and pharmacophore modeling. The best-fit candidate from the extracted molecules was compared to the chemical molecules used. The results indicated a similarity between the chemical and natural ligands which suggested the potential use of the natural product against vitiligo. The main finding of this research work was the discovery of a new molecule extracted from a natural plant and the detection of its anti-vitiligo activity using an in-silico approach. This method can significantly reduce the cost of searching for potential medicinal molecules

Clarification of purple carrot juice: analysis of the fouling mechanisms and evaluation of the juice quality

Purple carrot juice was clarified by microfiltration. Two modes of filtration, batch concentration and total recycle were tested and the effect of microfiltration process on permeate flux and membrane fouling was studied. Intrinsic membrane resistance was negligible compared with the fouling resistances, which was less than 5 % of total resistance. Determination of membrane hydraulic permeability showed that water cleaning could permit a recovery of about 7 % of initial hydraulic flux. The analysis of color parameters of feed, permeate and concentrate juice during filtration shows that the a* and b* values decrease for the permeate corresponding respectively to changes from green to red and from blue to yellow. The total sugar and reducing sugars increase in permeate and decrease in concentrate. This work showed that it was possible to clarify the purple carrot juice by microfiltration with a real amelioration of the juice appearance

Epidemiology and antibiotic resistance of Salmonella enterica Serovar Kentucky isolates from Tunisia: The new emergent multi-drug resistant serotype

International audienceSince 2002, the emergence of multidrug resistant Salmonella enterica serovar Kentucky (S. Kentucky) and the associated salmonellosis with treatment failure were declared in different parts of the world and were in most of the case contracted during travels to Northeast and Eastern Africa. In the present work, we reported an epidemiological study of S. Kentucky isolated from different environmental and clinical origins in Tunisia, using Pulsed-field gel electrophoresis (PFGE); Enterobacterial Repetitive Intergenic Consensus (ERIC-2) fingerprinting; Plasmid profiling; and antibiotic resistance profiles. ERIC-2 fingerprinting allowed the differentiation of 14 different patterns versus only 4 pulsotypes. Besides, a high proportion of strains were found to be nontypeable by XbaI-PFGE and/or by plasmid profiling (plasmid-free strains). The antibiotic resistance was mainly detected against streptomycin (80.7%), sulfonamides (42.1%) and tetracycline (15.7%). Furthermore, two avian strains were shown to be resistant to trimethoprim-sulfamethoxazole and three clinical strains have demonstrated multidrug-resistant phenotypes (against 5 to 10 antibiotics) and all of them exhibited resistance against nalidixic acid, ciprofloxacin, ofloxacin and tetracycline. ERIC-2 PCR was found to be the most discriminative. However, combination of the three typing methods offer a better mean for differentiating S. Kentucky isolates, monitoring the multiresistant types and determination of their origin. (C) 2011 Elsevier Ltd. All rights reserved