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Structure of the exopolysaccharide of Pseudomonas stutzeri strain ATCC 17588

Bacterial extracellular polysaccharides are known as a cell-bound capsule, a sheath, or a slime, which is excreted into the environment. They play an important role in virulence of medical bacteria and plant-to-symbiont interaction and are used for serotyping of bacteria and production of vaccines. Some exopolysaccharides have commercial applications in industry, and claims of health benefits have been documented for an increasing number of them. Exopolysaccharides have diverse composition and structure, and some contain sugar and non-sugar components that are found in bacterial carbohydrates only. The present article provides an updated collection of the data on exopolysaccharides of various classes of gram-negative and gram-positive bacteria reported until the end of 2019. When known, biosynthesis pathways of exopolysaccharides are treated in a summary manner. References are made to structure and biosynthesis relatedness between exopolysaccharides of different bacterial taxa as well as between bacterial polysaccharides and mammalian glycosaminoglycans.

Pseudomonas stutzeri AS22, when grown on media containing starch and yeast extract and incubated at 30 °C and 200 rpm for 24 h, was found to produce an acidic and high-molecular mass exopolysaccharide (EPS22). The EPS22 was purified and a yield of 1.3 g/l was achieved.

The average molecular mass of the EPS22 was determined by high-performance size-exclusion chromatography (HPSEC) and showed an average molecular mass of 9.9 × 10⁵ Da and a polydispersity index M_w/M_n (M_w, weight-average and M_n, number-average) of 1.197 ± 0.015. Structural data of this EPS22 were determined using a combination approach including monosaccharide composition (HPAEC–PAD and GLC), methylation analysis (GC–MS) and NMR spectroscopy analysis. EPS22 was found to be a complex heteropolysaccharide with a repeating unit mainly composed of glucose, mannose and lactyl rhamnose in a molar ratio of 1:1.1:0.7. The acidic nature of the polysaccharide is due to the presence of three non-osidic substituents consisting of a lactyl, acetyl, and pyruvyl groups.

Raoultella terrigena strain Ez-555-6, isolated from a root nodule of Medicago sativa harvested in the Chernobyl exclusion zone, produces a non-referenced high-molecular-mass exopolysaccharide (EPS). The structure of this EPS was determined using a combination approach including monosaccharide composition (GLC–FID, HPAEC–PAD), determination of glycosylation sites (GLC–EIMS) and 1D/2D NMR (¹H, ¹³C) and ESIMS (HR, MS/MS) studies of oligosaccharides obtained from mild acid hydrolysis. The EPS was found to be a charged pentasaccharide with a repeating unit composed of d-galactose, d-glucose, d-mannose and d-glucuronic acid (1:2:1:1). Lactic acid and O-acetyl substituents were localized on galactose and glucose residues, respectively, as presented in the following structure:

The flow properties of the polysaccharides produced by Haloferax mediterranei^T ATCC 33500 and its super mutant Haloferax mediterranei EPS⁺⁺, R4 and EPS⁺⁺ respectively, were investigated. The R4 repeating unit is a trisaccharide containing mannose and 2-acetamido-2-deoxyglucuronic acid, ester sulphate groups are also present. In order to compare the properties of both polymers viscosimetric measurements were carried out at different integration times and using different concentrations of polymer. Under the assayed experimental conditions no effect of the time applying stress is detected for either polymer. A strong pseudoplastic behaviour is observed which is increased as the polymer concentration rises. Differences in viscosity between both polymers are due to the different molecular weights. The correlation of the experimental data using a modification of the Cross model has given very good results.

An acidic exopolysaccharide was isolated from P. fluorescens strain H13. The structure of the polysaccharide repeating unit was determined using chemical methods and 1D and 2D NMR techniques. The repeating unit was characterized as a trisaccharide composed of d-glucose, 2-acetamido-2-deoxy-d-glucose and $\text{4-O-}\text{acetyl-2-acetamido-2-deoxy-}\text{d}\text{-mannuronic}$ acid.