1,721,057 research outputs found
Glutathione release in extracellular form by S. cerevisiae strains
Full text linkGlutathione (GSH, L--glutamyl-L-cysteinyl-glycine) is the most abundant non-protein thiol compound widely present in living organisms, from prokaryotes to eukaryotes (Anderson 1998). It is synthesised intracellularly by the consecutive actions of -glutamylcysteine synthetase, feedback inhibited by GSH, and GSH synthetase. This tripeptide’s very low redox potential gives it the properties of a cellular redox buffer (Udeh and Achremowicz 1997). In living tissues, GSH plays a pivotal role in bioreduction, protection against oxidative stress, xenobiotic and endogenous toxic metabolite detoxification, enzyme activity and sulphur and nitrogen metabolism (Penninckx 2002). These characteristics make this active tripeptide an important aid and/or support for the treatment of numerous diseases, such as HIV infections, liver cirrhosis, pancreatic inflammations and aging (Wu et al., 2004). In addition, GSH is of interest in the food additive industry and sports nutrition (Lomaestro and Malone 1995).
Yeasts, in particular belonging to the genus Saccharomyces, are the most commonly used microorganisms on an industrial scale for GSH fermentative production; however GSH contents of the wild-type strains are usually variable (0.1 – 1% dw) and always in intracellular form (Rollini and Manzoni 2006).
The present research was aimed at obtaining GSH in extracellular form, released from cells, at high levels. Samples of S. cerevisiae (baker’s yeast) from different suppliers were tested, together with reference strains belonging to international collections. Cells were comparatively treated employing physical and chemical procedures. The best result (2.9 g/l, 90% of produced GSH in extracellular form) was achieved at 24 h reaction, employing lyophilised cells from compressed baker’s yeast. The possibility of obtaining GSH directly in extracellular form, skipping the downstream cell extraction step, represents an interesting opportunity of reducing GSH production cost and furthering the range of application and utilization of this molecule
Influence of different fermentation parameters on glutathione volumetric productivity by Saccharomyces cerevisiae
No full textA full factorial experimental design was carried out, with the aim of combining the best fermentation conditions for S. cerevisiae cell growth, with the most important parameters affecting glutathione GSH intracellular accumulation. Conditions favouring cell growth (max. 10.5 g dw/l) were identified as (g/l) beet molasses 80, ammonium sulphate 1, magnesium sulphate 0.2, and temperature 30 degrees C. These results were in contrast to what found to enhance GSH intracellular levels (max. 1.85% dw), identified as (g/l) molasses 20, ammonium sulphate 5, magnesium sulphate 1.2, temperature 24 degrees C. By calculating GSH volumetric productivity (mg/l day), it was possible to evidence the best conditions (GSH max. 81 mg/l day) allowing cell growth to be maximised, 80 g/l (high level) molasses and 1 g/l (low level) ammonium sulphate, and GSH accumulation, employing a magnesium sulphate concentration set at 1.2 g/l (high level). The possibility of obtaining S. cerevisiae cells with a high GSH intracellular content (up to 1.85% dw) can be considered an interesting opportunity of furthering the range of application and utilization of this molecule. (c) 2006 Elsevier Ltd. All rights reserved
Biotransformation of D-galactitol to tagatose by acetic acid bacteria
No full textTagatose, a ketohexose C-4 fructose epimer present in nature in low concentration, is a potential low calorie bulking sweetener that can be obtained by the microbial oxidation of the corresponding polyalcohol galactitol. The screening of strains belonging to the acetic acid bacteria resulted in 100-160 mg tagatose/1, produced at 24 h in non growing conditions, while 260-340 mg tagatose/1 was obtained at 48 h with growing cells of Gluconobacter strains, with a specific activity rate of tagatose production, 1.4 × 10-3 1/h. After galactitol adaptation the Gluconobacter oxydans DSM 2343 strain gave a notable increase in tagatose yield, reaching 3160 mg/1 with a corresponding 6.6 × 10-3 1/h specific activity rate at 24 h of reaction. Preliminary enzyme characterisation experiments indicated that the dehydrogenase activity may be attributable to a sorbitol dehydrogenase (SDH)
Isolation and characterization of the exopolysaccharide produced by Daedalea quercina
No full textThe production of exopolysaccharide (EPS) by a strain of the basidiomycete Daedalea quercina was investigated. Of seven different carbon sources, glucose and dextrins gave the highest crude polysaccharide yield (4.7-5 g 1-1, 55-60% carbohydrate content) in shake-flask cultures, at 14 days of fermentation. Experiments carried out in a 101 fermenter, at two different agitation speeds, gave the best results at 300 rpm, resulting in 12-14 g 1-1 of crude exopolysaccharide in 9-11 days. Fractionation of the EPS samples, carried out by tangential flow ultrafiltration, evidenced a single EPS fraction (MW > 30 000 Da) in samples from glucose, while two fractions (MW > 30 000 Da and 30 000 > MW > 10 000 Da) were present in samples from dextrins. Fractions characterization by HPLC and proton NMR spectroscopy revealed diversity in composition and structure in the obtained EPS: from glucose mainly an α-linked mannan, and from dextrins mainly an α- and β-linked glucan
Improvement of Intracellular Glutathione content in Baker’s Yeast for Nutraceutical Application
No full textThe study was aimed at investigating the best conditions to increase intracellular GSH levels in samples of baker’s yeast (S. cerevisiae), employed either in compressed and dried form. Glucose, GSH precursors amino acids (cysteine, glycine and glutamic acid), as well as other cofactors, were dissolved in a biotransformation solution in which yeast cells were added (5% dcw). Two response surface central composite designs (RSCCD) were performed in sequence: in the first step the influence of amino acid composition (cysteine, glycine, glutamic acid and serine) on GSH accumulation was investigated; once setup their formulation, the influence of other components was studied. GSH accumulation ability of baker’s yeast in compressed form was found higher at the beginning of shelf life, i.e. in the first week, and a maximum of 2.04%dcw was obtained. Performance of yeast in dried form was not found satisfactory, as the maximum GSH level was 1.18%dcw. When cysteine lacks from the reaction solution, yeast cells did not accumulate GSH. With dried yeast, the highest GSH yields occurred when cysteine was set at 3 g/L, glycine and glutamic acid at least at 4 g/L and serine minimized. Employing compressed yeast, the highest GSH yields occurred when cysteine and glutamic acid were set at 2-3 g/L, while glycine and serine higher than 2 g/L. Results allowed to setup an optimal and feasible procedure to obtain GSH-enriched yeast biomass, with up to 3-fold increase respect to initial content
Influence of medium design on lovastatin and mevastatin production by Aspergillus terreus strains
No full textIn order to investigate the influence of medium design on lovastatin and mevastatin production by Aspergillus terreus strains, several nitrogen complex sources, such as vegetal flour and peptones of different origin (animal and vegetal) were tested, together with the addition of methionine, an aminoacid that is directly involved in lovastatin biosynthetic pathway. Soybean peptone generally allowed the best lovastatin yields to be achieved (250-280 mg l(-1)), particularly in the presence of soybean and peanut flours. For mevastatin, the best results (300-320 mg l(-1)) were obtained at 7 days fermentation with modified base medium (CLD), and at 14 days with standard medium (STD), not being possible in this case to associate the best yield with a defined flour and/or peptone. The results show that lovastatin production is influenced by the presence of soybean peptone and by the addition of methionine; instead, the production of mevastatin appears more strictly strain-associated and not directly dependent on the complex ingredients employed
Biosynthesis and biotechnological production of statins by filamentous fungi and application of these cholesterol-lowering drugs
No full textHypercholesterolemia is considered an important risk factor in coronary artery disease. Thus the possibility of controlling de novo synthesis of endogenous cholesterol, which is nearly two-thirds of total body cholesterol, represents an effective way of lowering plasma cholesterol levels. Statins, fungal secondary metabolites, selectively inhibit hydroxymethyl glutaryl-coenzyme A (HMG-CoA) reductase, the first enzyme in cholesterol biosynthesis. The mechanism involved in controlling plasma cholesterol levels is the reversible inhibition of HMG-CoA reductase by statins, related to the structural similarity of the acid form of the statins to HMG-CoA, the natural substrate of the enzymatic reaction. Currently there are five statins in clinical use. Lovastatin and pravastatin (mevastatin derived) are natural statins of fungal origin, while symvastatin is a semi-synthetic lovastatin derivative. Atorvastatin and fluvastatin are fully synthetic statins, derived from mevalonate and pyridine, respectively. In addition to the principal natural statins, several related compounds, monacolins and dihydromonacolins, isolated fungal intermediate metabolites, have also been characterized. All natural statins possess a common polyketide portion, a hydroxy-hexahydro naphthalene ring system, to which different side chains are linked. The biosynthetic pathway involved in statin production, starting from acetate units linked to each other in head-to-tail fashion to form polyketide chains, has been elucidated by both early biogenetic investigations and recent advances in gene studies. Natural statins can be obtained from different genera and species of filamentous fungi. Lovastatin is mainly produced by Aspergillus terreus strains, and mevastatin by Penicillium citrinum. Pravastatin can be obtained by the biotransformation of mevastatin by Streptomyces carbophilus and simvastatin by a semi-synthetic process, involving the chemical modification of the lovastatin side chain. The hypocholesterolemic effect of statins lies in the reduction of the very low-density lipoproteins (VLDL) and LDL involved in the translocation of cholesterol, and in the increase in the high-density lipoproteins (HDL), with a subsequent reduction of the LDL- to HDL-cholesterol ratio, the best predictor of atherogenic risk. The use of statins can lead to a reduction in coronary events related to hypercholes-terolemia, but the relationship between benefit and risk, and any possible interaction with other drugs, must be taken into account
Produzione di metaboliti coinvolti nei meccanismi di detossificazione in cellule di lievito
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