Structural determination and NMR characterization of a bacterial exopolysaccharide.

A strain of Bacillus licheniformis with high exopolysaccharide (EPS) production ability was isolated and identified. A new type of EPS was isolated from the strain fermentation and its structural characteristics were investigated and elucidated by partial and total acid hydrolysis, Fourier transform infrared, and (1)H and (13)C NMR spectroscopy including 2D (1)H, COSY, NOESY, XHCOR and HMBC experiments. Based on obtained data, the EPS was found to be a levan composed of linear chains of (2→6)-linked ß-d-fructofuranosyl residues with connections ß (2→6).

Antioxidant effect of nondigestible levan and its impact on cardiovascular disease and atherosclerosis.

Levan polysaccharide, a type of fructan, has been shown to favorably affect diabetes type 2 and hypercholesterolemia. Recent reports have indicated that excessive oxidative stress contributes to the development of atherosclerosis linked metabolic syndrome. The objective of this current study was to investigate the possible protection against oxidative stress linked atherosclerosis. A group of twenty four male rats was divided into four subgroups; a normal diet group (Control), normal rats received levan (L), a high-cholesterol diet group (Chol) and a high-cholesterol diet with 5% (w/w) levan group. After the treatment period, the plasma antioxidant enzymes and lipid profiles were determined. Our results show that treatment with levan positively changed plasma antioxidant enzyme activities by increasing superoxide dismutase (SOD) and catalase (CAT) by 40% and 28%, respectively, in heart. Similarly, the treatment of Chol fed groups with levan positively changed lipid profiles by decreasing total cholesterol, triglycerides and LDL-cholesterol by 50%, 38.33% and 64%, respectively. Thus may have potential antioxidant effects and could protect against oxidative stress linked atherosclerosis.

Microbial production of levanase for specific hydrolysis of levan.

A newly isolated bacterial strain from Tunisian thermal source was selected for its ability to produce extracellular levanase when grown on levan substrate. The optimization of carbon source, nitrogen source, temperature and initial pH of the growth medium in submerged liquid cultures were investigated. In fact, levan was found to be a good inducer of levanase enzymes. The optimal temperature and pH of the levanase activity were 40 °C and 6.4, respectively. This enzyme exhibited a remarkable stability and retained 75% of its original activity at 55 °C for more than 1 h at pH 6.4. Crude enzyme of the strain rich in levanase was established for the hydrolysis of levan in order to produce fructooligosaccharides with variable degrees of polymerization which could be used in important fields such medicine, food-processing industry and cosmetic. The extracellular levanase of the strain was then, partially purified as determined by SDS-PAGE. The purification was achieved by ammonium sulfate precipitation, gel filtration and DEAE cellulose chromatographies.

Antioxidant and antimicrobial activities of Lycium shawii fruits extract.

Crude extracts from the fruit of Lycium shawii, a plant collected from the south of Tunisia, were screened for their in vitro antioxidant, antimicrobial and antifungal activities. The dried fruits were extracted with EtOH and an aqueous suspension of the obtained EtOH extract was partitioned successively with CHCl3, CH2Cl2, EtOAc and n-BuOH, leaving residual water extract. Total phenolic content of extracts from these fruits were also determined. ß-Carotene bleaching assay and Folin-Ciocalteu reagent were used to determine total antioxidant activity and total phenols of fruit extracts. Total phenolic and flavonoid contents varied from 100 to 377 mg GAE/g DW and 3.3-110.6 mg quercetin/gDW, respectively. Several extracts showed high antioxidant capacity and an antimicrobial activity against different strains. This is, to our knowledge, the first report on the detail chemical composition, antioxidant and antimicrobial activities of L. shawii extracts. The results provided evidence that the studied fruit might indeed be potential sources of natural antioxidant and antimicrobial agents.

Microbial production of levansucrase for synthesis of fructooligosaccharides and levan.

A newly isolated thermophilic bacterial strain from Tunisian thermal source was identified as Bacillus sp. and was selected for its ability to produce extracellular levansucrase. Following the optimization of carbon source, nitrogen source, temperature and initial pH of the growth medium in submerged liquid cultures. In fact, sucrose was found to be a good inducer of levansucrase enzymes. The optimal temperature and pH of the levansucrase were 50°C and 6.5, respectively and its activity increased four folds in the presence of 50mM Fe(2+). This enzyme exhibited a remarkable stability and retained 100% of its original activity at 50°C for more than 1h at pH 6.5. The half-life of the enzyme was 1h at 90°C. Crude enzyme of Bacillus sp. rich in levansucrase was established for the synthesis of fructooligosaccharides and levan. Bacillus sp. could therefore be considered as a satisfactory and promising producer of thermostable levansucrases. Contrary to other levansucrases, the one presented in the current study was able to produce high levels of levan with high molecular weight at 50°C and having an important effect as a hypoglycemic agent which was demonstrated in our previous publications (Dahech et al., 2011 [25]) and as a hypo-cholesterolemic agent which will be investigated in further research.

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).

Hypolipidemic effect of diet supplementation with bacterial levan in cholesterol-fed rats.

Levan polysaccharide, a type of fructan, has been shown to have industrial applications as a new industrial gum in the fields of cosmetics, foods like dietary fiber and pharmaceutical goods. The objective of this current study was to investigate the possible hypolipidemic and antioxidative effects of levan in rats fed with a high-cholesterol diet. Animals were allocated into four groups of six rats each: a normal diet group (Control), normal rats received levan (L), a high-cholesterol diet group (Chol) and a high-cholesterol diet with a daily dose of levan equivalent to 5%. Treated hypercholesterolemic rats were administrated with levan in drinking water through oral gavage for 60 days. After the treatment period, the plasma antioxidant enzymes and lipid profiles were determined. Our results show that treatment with levan polysaccharide positively changed plasma antioxidant enzyme activities and lipid profiles (total cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides) in cholesterol-rats, and thus may have potential hypolipidemic and antioxidant effects. Levan could protect against oxidative stress linked atherosclerosis and decrease the atherogenic index.

Antidiabetic activity of levan polysaccharide in alloxan-induced diabetic rats.

This study aims to examine the effects of polysaccharide levan on oxidative stress and hyperglycemia in alloxan-induced diabetic rats. Levan, used in this study, was a microbial levan synthetisized by a non pathogenic bacteria recently isolated and identified as Bacillus licheniformis. Animals were allocated into four groups of six rats each: a control group (Control), diabetic group (Diab.), normal rats received levan (L) and diabetic rats fed with levan (DL). Treated diabetic rats were administrated with levan in drinking water through oral gavage for 60 days. The administration of polysaccharide levan in diabetic rats caused a significant increase in glycogen level by 52% and a decrease in glucose level in plasma by 52%. Similarly, the administration of polysaccharide levan in diabetic rats caused a decrease in the thiobarbituric acid-reactive substances (TBARS) by 31%, 41%, 39% and 25%, an increase in superoxide dismutase (SOD) by 40%, 50%, 44% and 34%, and in catalase (CAT) by 18%, 20%, 12% and 18% in liver, kidney, pancreas and heart, respectively. Furthermore, a significant decrease in hepatic and renal indices toxicity was observed, i.e. alkalines phosphatases (ALP), aspartate and lactate transaminases (AST and ALT) activities, total bilirubin, creatinine and urea levels by 19%, 31%, 32%, 36%, 37% and 23%, respectively. The results show that administration of polysaccharide levan can restore abnormal oxidative indice near normal levels. This study demonstrates, for the first time, that polysaccharide levan is efficient in inhibiting hyperglycemia and oxidative stress induced by diabetes and suggests that levan supplemented to diet may be helpful in preventing diabetic complications in adult rats.

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.