Molecular Aspects of Anti-Polysaccharide Antibody Responses
Maurizio Zanetti, J. Donald Capra in The Antibodies, 2002
Levans are neutral polymers of fructose joined by either (3(2 : 6) or (3(2 : 1) linkages. Plant levans, made for energy storage, are linear polymers with either predominantly p(2 : 6) linkages (monocotyledons, e.g., rye grass) or predominantly (3(2 : 1) linkages, also known as inulin (dicotyledons, e.g., Jerusalem artichokes; [50]). Bacterial levans (BL) are extra-cellular products of microbial fermentation by Bacillus and Erwinia sp. bacteria which synthesize levan from sucrose and secrete it [51]. BL is much larger (Mr 106 Daltons) than plant levans, is readily soluble in water, and consists of a backbone of (3(2: 6) linked fructose with branches of (3(2 : 1)-linked fructose.
Exopolysaccharide Production from Marine Bacteria and Its Applications
Se-Kwon Kim in Marine Biochemistry, 2023
Dextran and levan are extracellularly synthesized polysaccharides. The synthesis of dextran, levan and their derivatives is directly induced in the presence of sucrose (Schmid et al., 2015). The most common sucrase activity–based polymer is dextran, which mainly consists of α-(1–6) linked glucose. Dextran-based polymer is released outside the cell by the dextransucrase, the key enzyme for dextran synthesis (Schmid et al., 2015). Levan, which is produced by levansucrases, can also act as fructose transferases producing polyfructan (levan). Table 18.1 shows various bacterial EPSs, their sugar components and the transport mechanism.
Gut Bacteroides species in health and disease
Published in Gut Microbes, 2021
The OMVs of Bth contain glycosyl hydrolases that help in the degradation of levan, a common non-structural carbohydrate in plants. The by-products of levan degradation include extracellular fructo-oligosaccharides that are important for the growth of other Bacteroides spp.33–35 Another example of OMV-associated intra-genus support involves Bacteroides ovatus and Bacteroides vulgatus. The glycosyl hydrolases in the OMVs of B. ovatus break down inulin, the products of which are utilized by B. vulgatus.36 Thus, the genus Bacteroides is an efficient public goods provider, and its services generally support other species in the microbial gut community.
Biofilm-based delivery approaches and specific enrichment strategies of probiotics in the human gut
Published in Gut Microbes, 2022
Jie Gao, Faizan Ahmed Sadiq, Yixin Zheng, Jinrong Zhao, Guoqing He, Yaxin Sang
Prebiotics containing levan can be specifically utilized by Bacteroides thetaiotaomicron.147 Similarly, yeast mannan (indigestible water-soluble polysaccharide) has been reported to specifically promote the growth of B. thetaiotaomicron and B. ovatus in trials based on human colonic microbiota model.148 Soluble dietary fiber (10% inulin) reportedly enhances growth and abundance of Bacteroides fragilis with a concomitant increase in IgA.149
Metabolomics in the prevention and management of asthma
Published in Expert Review of Respiratory Medicine, 2019
Zhaozhong Zhu, Carlos A. Camargo, Kohei Hasegawa
Despite the clinical and public health importance of asthma [5], the molecular determinants of asthma pathogenesis are not yet fully understood [6]. One of the most important genomic regions that are associated with asthma development is chromosome 17q21. This region contains the genetic variants that regulate ORMDL3 gene expression, which plays an important role in sphingolipid metabolism. Indeed, Zhang et al. showed, by using a human lung epithelial cell model, that siRNA knockdown of ORMDL3 modulates the activity of serine palmitoyltransferase which is involved in the rate-limiting step of the production of sphingolipids and increases sphingolipid metabolism, such as increased ceramides and sphingosine-1-phosphate (S1P) level [7]. This finding is consistent with prior findings of ORMDL3 and sphingolipid metabolism in mouse airway epithelium [8] and ORMDL3 transgenic mice models [9]. Also a recent study by Kelly et al. suggested that prenatal vitamin D supplementation may lower the risk of recurrent wheeze by age 3 years through alterations of sphingolipid metabolite levels depending on the ORMDL3 genotype [10]. Additionally, our recent studies demonstrated that increased levels of sphingolipid metabolites in infants’ nasopharyngeal airway and serum are associated with higher bronchiolitis severity – one of the most important risk factors for asthma development [11,12]. Furthermore, a cross-sectional study of 325 Costa Rican children with asthma used transcriptomic and metabolomic data, and discovered associations of ORMDL3 and dysregulated sphingolipid metabolism in blood with impaired lung function [13]. In addition to the host-derived metabolites, the microbe-derived metabolites may also play a role in the asthma pathobiology. For example, Levan et al. reported that gut microbes produce 12,13-diHOME – a metabolite that decreases the number of regulatory T cells in the lungs and promotes airway inflammation in asthma [14]. Together, these studies suggest an integrated role of host genetics (e.g. ORMDL3 gene), microbiome and their related metabolites in the development of childhood asthma.
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