Dietary Supplementation of Microbial Dextran and Inulin Exerts Hypocholesterolemic Effects and Modulates Gut Microbiota in BALB/c Mice Models.

Microbial exopolysaccharides (EPSs), having great structural diversity, have gained tremendous interest for their prebiotic effects. In the present study, mice models were used to investigate if microbial dextran and inulin-type EPSs could also play role in the modulation of microbiomics and metabolomics by improving certain biochemical parameters, such as blood cholesterol and glucose levels and weight gain. Feeding the mice for 21 days on EPS-supplemented feed resulted in only 7.6 ± 0.8% weight gain in the inulin-fed mice group, while the dextran-fed group also showed a low weight gain trend as compared to the control group. Blood glucose levels of the dextran- and inulin-fed groups did not change significantly in comparison with the control where it increased by 22 ± 5%. Moreover, the dextran and inulin exerted pronounced hypocholesterolemic effects by reducing the serum cholesterol levels by 23% and 13%, respectively. The control group was found to be mainly populated with Enterococcus faecalis, Staphylococcus gallinarum, Mammaliicoccus lentus and Klebsiella aerogenes. The colonization of E. faecalis was inhibited by 59-65% while the intestinal release of Escherichia fergusonii was increased by 85-95% in the EPS-supplemented groups, respectively, along with the complete inhibition of growth of other enteropathogens. Additionally, higher populations of lactic acid bacteria were detected in the intestine of EPS-fed mice as compared to controls.

Production of a high molecular weight levan by Bacillus paralicheniformis, an industrially and agriculturally important isolate from the buffalo grass rhizosphere.

A new exopolysaccharide (EPS) producing Gram-positive bacterium was isolated from the rhizosphere of Bouteloua dactyloides (buffalo grass) and its EPS product was structurally characterized. The isolate, designated as LB1-1A, was identified as Bacillus paralicheniformis based on 16S rRNA gene sequence and phylogenetic tree analysis. The EPS produced by LB1-1A was identified as a levan, having ß(2 → 6) linked backbone with ß(2 → 1) linkages at the branch points (4.66%). The isolate LB1-1A yielded large amount (~ 42 g/l) of levan having high weight average molecular weight (Mw) of 5.517 × 107 Da. The relatively low degree of branching and high molecular weight of this levan makes B. paralicheniformis LB1-1A a promising candidate for industrial applications.

Growth Inhibition of Common Enteric Pathogens in the Intestine of Broilers by Microbially Produced Dextran and Levan Exopolysaccharides.

Antibiotics are generally applied for treatment or as subtherapeutic agents to overcome diseases caused by pathogenic bacteria including Escherichia coli, Salmonella and Enterococcus species in poultry. However, due to their possible adverse effects on animal health and to maintain food safety, probiotics, prebiotics, and synbiotics have been proposed as alternatives to antibiotic growth promoters (AGPs) in poultry production. In this study, the effects of prebiotics on the augmentation of broiler's indigenous gut microbiology were studied. Day old 180 broilers chicks were divided into four treatment groups: G, L, C1, and C2. The groups G and L were fed with basal diet containing 3% dextran and 3% levan, respectively. Control groups were fed with basal diets without antibiotic (C1) and with antibiotics (C2). The experimental groups showed decreased mortality as compared to control groups. After 35 days, the chickens were euthanized and intestinal fluid was analyzed for enteric pathogens on chromogenic agar plates and by 16S rRNA gene sequencing. Inhibition of the growth of E. coli and Enterococcus was observed in groups G and L, respectively, whereas Salmonella was only present in group C1. Also, high populations of lactic acid bacteria were detected in the intestine of prebiotic fed birds as compared to controls. These results depict that dextran and levan have the potential to replace the use of antibiotics in poultry feed for inhibiting the growth of common enteric pathogens. To the best of our knowledge, this is the first study where effects of dextran and levan on intestinal microbiota of broilers have been reported.

Production of bimodal molecular weight levan by a Lactobacillus reuteri isolate from fish gut.

An exopolysaccharide (EPS) synthesizing potentially probiotic Gram-positive bacterial strain was isolated from fish (Tor putitora) gut, and its EPS was structurally characterized. The isolate, designated as FW2, was identified as Lactobacillus reuteri through 16S rRNA gene sequencing and phylogenetic analysis. This isolate produces fructan-type EPS using sucrose as a substrate. Based on 13C-NMR spectroscopy, methylation analysis and monosaccharide composition, the EPS was identified as a linear levan polymer with fructose as main constituent linked via ß(2 → 6) linkages. Based on molecular weight (MW) distribution, two groups of levan were found to be produced by the isolate FW2: one with high MW (4.6 × 106 Da) and the other having much lower MW (1.2 × 104 Da). The isolate yielded about 14 g/L levan under optimized culturing parameters including aeration conditions, pH, temperature and substrate concentration. The obtained bimodal molecular weight linear levan is the first of its type to be synthesized by a L. reuteri isolate from fish gut. Bimodal molecular weight prebiotic levan together with the probiotic potential of the producing strain would provide a new promising synbiotic combination for use in aqua culture.

Raman spectroscopy for the analysis of different exo-polysaccharides produced by bacteria.

In this study, Raman spectroscopy is employed for the characterization and comparison of two different classes of exo-polysaccharides including glucans and fructans which are produced by different bacteria. For this purpose, nine samples are used including five samples of glucans and four of fructans. Raman spectral results of all these polysaccharides show clear differences among various glucans as well as fructans showing the potential of this technique to identify the differences within the same class of the compounds. Moreover, these two classes are also compared on the basis of their Raman spectral data and can be differentiated on the basis of their unique Raman features. Multivariate data analysis techniques, Principle Component Analysis (PCA) is found very helpful for the comparison of the Raman spectral data of these classes of the carbohydrates.