Oral administration of levan polysaccharide reduces the alloxan-induced oxidative stress in rats

This study aimed to evaluate the effect of a polysaccharide named levan, which was produced by new isolated bacteria, on oxidative stress and hyperglycemia in alloxan-induced diabetic rats. Levan polysaccharide was given in drinking water for 60 days at a daily dose equivalent to 2%. The oral administration of levan in diabetic rats caused a decrease in glucose level in plasma and an increase of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) activities in both pancreas and liver. Furthermore, a protective action against hepatic and pancreatic toxicity in diabetic rats was clearly observed. Furthermore, a significant decrease in hepatic and pancreatic indices toxicity was observed, i.e., alkalines phosphatases (ALP), aspartate and lactate transaminases (AST and ALT), lactate deshydrogenases (LDH) activities and the thiobarbituric acid-reactive substances (TBARs). These beneficial effects of levan were confirmed by histological findings in hepatic and pancreatic tissues of diabetic rats. This study demonstrates for the first time that levan is efficient in inhibiting hyperglycemia and oxidative stress induced by diabetes and suggests that administration of levan may be helpful in the prevention of diabetic complications associated with oxidative stress.     

Stabilization of Penicillium occitanis cellulases by spray drying in presence of Maltodextrin

The stabilization of fungal cellulases by spray drying, the thermal stability of Penicillium occitanis cellulases and the effect of some additives were studied. We observed that CMCase activity presents a good stability at 50 degrees C, even after 60 h of incubation. On the other hand, beta-glucosidase activity was more sensitive (loss of 50%) and reacts on total cellulases activities (Filter paper activities). The addition of hydrophilic agents such as ethylene glycol, polyethylene glycol (PEG6000) enhanced enzyme activity. The effect of PEG and Maltodextrin, another water activity decreasing agent, were then tested during the spray drying of Pol6 cellulases. The presence of 1% PEG allowed the best recovery but had a negative effect on enzyme stability while 1% Maltodextrin showed a negative effect on enzyme recovery but a very positive effect on enzyme stabilization.     

Construction of a new strain of Streptomyces violaceoniger,having strong,constitutive and stable glucose-isomerase activity

Summary A newly isolated strong Streptomyces promoter (P1) has been cloned in front of the xylA gene of Streptomyces violaceoniger. This led to a strong and constitutive expression. To avoid instability of plasmid and glucose isomerase activity, the P1-xylA gene has been integrated into the chromosome using the integrative vector pTS55. The resultant CBS1 strain has about seven times higher glucose-isomerase activity in absence of xylose compared to that of wild type strain fully induced by xylose. In addition, glucose isomerase specific activity of the CBS1 strain increases in the secondary growth phase, in contrast to wild type strain.     

Galactolipase activity of Talaromyces thermophilus lipase on galactolipid micelles,monomolecular films and UV-absorbing surface-coated substrate

Talaromyces thermophilus lipase (TTL) was found to hydrolyze monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) substrates presented in various forms to the enzyme. Different assay techniques were used for each substrate: pHstat with dioctanoyl galactolipid-bile salt mixed micelles, barostat with dilauroyl galactolipid monomolecular films spread at the air-water interface, and UV absorption using a novel MGDG substrate containing α-eleostearic acid as chromophore and coated on microtiter plates. The kinetic properties of TTL were compared to those of the homologous lipase from Thermomyces lanuginosus (TLL), guinea pig pancreatic lipase-related protein 2 and Fusarium solani cutinase. TTL was found to be the most active galactolipase, with a higher activity on micelles than on monomolecular films or surface-coated MGDG. Nevertheless, the UV absorption assay with coated MGDG was highly sensitive and allowed measuring significant activities with about 10?ng of enzymes, against 100?ng to 10?μg with the pHstat. TTL showed longer lag times than TLL for reaching steady state kinetics of hydrolysis with monomolecular films or surface-coated MGDG. These findings and 3D-modelling of TTL based on the known structure of TLL pointed out to two phenylalanine to leucine substitutions in TTL, that could be responsible for its slower adsorption at lipid-water interface. TTL was found to be more active on MGDG than on DGDG using both galactolipid-bile salt mixed micelles and galactolipid monomolecular films. These later experiments suggest that the second galactose on galactolipid polar head impairs the enzyme adsorption on its aggregated substrate.     

Agricultural wastes as substrates for β-glucosidase production by Talaromyces thermophilus: Role of these enzymes in enhancing waste paper saccharification

In the present study, we investigated a potent extracellular β-glucosidases secreted by the thermophilic fungal strain AX4 of Talaromyces thermophilus, isolated from Tunisian soil samples. This strain was selected referring to the highest thermostability of its β-glucosidases compared to the other fungal isolates. The β-glucosidase production was investigated by submerged fermentation. The optimal temperature and initial pH for maximum β-glucosidase production were 50°C and 7.0, respectively. Several carbon sources were assayed for their effects on β-glucosidase production, significant yields were obtained in media containing lactose 1% (3.0?±?0.36?U/ml) and wheat bran 2% (4.0?±?0.4?U/ml). The combination of wheat bran at 2% and lactose at 0.8% as carbon source enhanced β-glucosidase production, which reached 8.5?±?0.28?U/ml. Furthermore, the β-glucosidase-rich enzymatic juice of T. thermophilus exhibited significant synergism with Trichoderma reesei (Rut C30) cellulases for pretreated waste paper (PWP) hydrolysis. Interestingly, the use of this optimal enzymatic cocktail increased 4.23 fold the glucose yield after saccharification of waste paper. A maximum sugar yield (94%) was reached when using low substrate (2%) and enzyme loading (EC1).     

Gene cloning and molecular characterization of the Talaromyces thermophilus lipase catalyzed efficient hydrolysis and synthesis of esters

A genomic bank from Talaromyces thermophilus fungus was constructed and screened using a previously isolated fragment lipase gene as probe. From several clones isolated, the nucleotide sequence of the lipase gene (TTL gene) was completed and sequenced. The TTL coding gene consists of an open reading frame (ORF) of 1083 bp encoding a protein of 269 Aa with an estimated molecular mass of 30 kDa. The TTL belongs to the same gene family as Thermomyces lanuginosus lipase (TLL, Lipolase®), a well known lipase with multiple applications. The promoter sequence of the TTL gene showed the conservation of known consensus sequences PacC, CreA, Hap2-3-4 and the existence of a particular sequence like the binding sites of Oleate Response Element (ORE) and Fatty acids Responsis Element (FARE) which are similar to that already found to be specific of lipolytic genes in Candida and Fusarium, respectively. Northern blot analysis showed that the TTL expression was much higher on wheat bran than on olive oil as sole carbon source. Compared to the Lipolase®, this enzyme was found to be more efficient for the hydrolysis and the synthesis of esters; and its synthetic efficiency even reached 91.6% from Waste Cooking Oil triglycerides.     

Partial purification of a Bacillus licheniformis levansucrase producing levan with antitumor activity

The extracellular fructosyltransferase (FTase) of a novel strain of Bacillus licheniformis capable of producing fructooligosaccharides (FOS) and a polysaccharide type levan was obtained and partially purified. The purification was achieved by ammonium sulfate precipitation, DEAE cellulose and gel filtration chromatographies. The enzyme was partially purified as determined by SDS-PAGE, and the specific activity reached was 67.5, representing a purification factor of 177 and yield of 40%. Levan was isolated from the cultures of B. licheniformis. The levan was composed mainly of fructose residues when analyzed by TLC after acid hydrolysis and NMR analysis. In a previous study, the levan produced exhibited a hypoglycemiant activity. The present paper deals with the study of the antitumor and anti-cytotoxic effect of levan produced by B. licheniformis strain. In the in vitro antitumor activity test of levan against some tumor cell lines, relatively the significantly high activity was observed against the HepG(2).     

Physiological and ultrastructural responses of sour orange (Citrus aurantium L.) clones to water stress

Water stress is a major abiotic constraint leading to serious crop losses. Recently, in the Mediterranean region, water stress has become markedly sensed, especially in Citrus orchards. This study investigated the physiological responses of local sour orange (Citrus aurantium L.) clones to severe water stress. Water stress was applied by withholding irrigation during weeks, followed by a rewatering phase during three months. Under water stress, sour orange clones decreased their stomatal conductance, net photosynthetic rate, and transpiration rate. On the contrary, biomass was stable, especially in the Kliaa clone. In addition, reduced leaf water potentials (-3 MPa) and water contents were measured in most of the clones, except Kliaa which kept the highest water potential (-2.5 MPa). After rewatering, all clones recovered except of the Ghars Mrad (GM) clone. Ultrastructural observations of leaf sections by transmission electron microscopy did not reveal marked alterations in the mesophyll cells and chloroplast structure of Kliaa in comparison to the sensitive clone GM, in which palisade parenchyma cells and chloroplasts were disorganized. This contrasting behavior was mainly attributed to genetic differences as attested by molecular analysis. This study highlighted GM as the drought-sensitive clone and Kliaa as the tolerant clone able to develop an avoidance strategy based on an efficient stomatal regulation. Although a high percentage of polyembryony characterizes C. aurantium and justifies its multiplication by seeds, heterogeneous water-stress responses could be observed within sour orange plants in young orchards.     

An enzyme electrode for on-line determination of ethanol and methanol

Since a stable alcohol oxidase with a high specific activity is not commercially available, we propose to produce and purify this enzyme from a strain of the yeast Hansenula polymorpha. This alcohol oxidase was immobilized into a gelatin matrix and its activity was estimated by a pO(2) sensor. The enzyme electrode obtained was then used in a continuous flow system to measure methanol or ethanol concentrations. The sample oxygen content dependence of the signal was minimized by the support properties. Measuring time for each sample were less than two minutes including response data treatment and rinsing step. The enzyme electrode response was set for ethanol from 0.5mM to 15mM and for methanol from 10mM to 300mM. On repeated use, the electrode signal for 10mM of ethanol was stable for at least 500 assays. Analysis have been performed in different beverages such as wine and beer, and the results compared to those obtained with classical methods of analysis.