epiglucan and succinoglycan

Agrobacterium is a genus of gram-negative bacteria that can produce several typical exopolysaccharides with commercial uses in the food and pharmaceutical fields. In particular, succinoglycan and curdlan, due to their good quality in high yield, have been employed on an industrial scale comparatively early. Exopolysaccharide biosynthesis is a multiple-step process controlled by different functional genes, and various environmental factors cause changes in exopolysaccharide biosynthesis through regulatory mechanisms. In this mini-review, we focus on the genetic control and regulatory mechanisms of succinoglycan and curdlan produced by Agrobacterium. Some key functional genes and regulatory mechanisms for exopolysaccharide biosynthesis are described, possessing a high potential for application in metabolic engineering to modify exopolysaccharide production and physicochemical properties. This review may contribute to the understanding of exopolysaccharide biosynthesis and exopolysaccharide modification by metabolic engineering methods in Agrobacterium.

Topics: Agrobacterium; beta-Glucans; Gene Expression Regulation, Bacterial; Genes, Bacterial; Metabolic Engineering; Polysaccharides, Bacterial

The cyclic β-glucans and succinoglycans produced by rhizobia are required for nodulation during symbiosis with legume hosts. However, only gene deletion analyses have been used to investigate their biological importance. For future studies on the physiological activity of those during symbiosis, biochemical methods need to be developed with separate carbohydrate compounds. Here, we isolated and purified rhizobial cellular carbohydrates using various chromatographic methods. Purified cyclic β-glucans, cyclosophoraoses, were monofunctionalized with biotin using the following three steps: tosylation, azidation, and amination. The mono-6-amino-cyclosophoraoses were linked with biotinamidohexanoic acid N-hydroxysuccinimide ester. Succinoglycans and monomers were tagged with biotinamidocaproyl hydrazide at the reducing sugar via reductive amination. The resulting biotinylated rhizobial carbohydrates were characterized by Fourier transform infrared and nuclear magnetic resonance spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy, and electrospray ionization mass spectrometry. The resulting neoglycoconjugates can be used as solid probes to study putative plant receptors and for non-invasive imaging for in vivo tracing.

Topics: Amination; Azides; beta-Glucans; Biotinylation; Fabaceae; Polysaccharides, Bacterial; Rhizobium; Symbiosis

Agrobacterium isolated from soil samples produced two extracellular polysaccharides: succinoglycan, an acidic soluble polymer, and curdlan gum, a neutral, insoluble polymer. Maize glucose, cassava glucose, and maize maltose were used in fermentation medium to produce insoluble polysaccharide. Two Agrobacterium sp. strains which were used (ATCC 31749 and IFO 13140) in the production of insoluble exopolysaccharide presented equal or superior yields compared to the literature. The strain ATCC 31749 yielded better production when using maize maltose, whose yield was 85%, whereas strain IFO 13140 produced more when fed maize glucose, producing a yield of 50% (on reducing sugars).

Topics: beta-Glucans; Polysaccharides, Bacterial; Rhizobium; Solubility; Species Specificity; Zea mays

Agrobacterium isolated from soil samples produced two extracellular polysaccharides: succinoglycan, an acidic soluble polymer, and curdlan gum, a neutral, insoluble polymer. Maize glucose, cassava glucose, and maize maltose were used in fermentation medium to produce insoluble polysaccharide. Two Agrobacterium sp. strains which were used (ATCC 31749 and IFO 13140) in the production of insoluble exopolysaccharide presented equal or superior yields compared to the literature. The strain ATCC 31749 yielded better production when using maize maltose, whose yield was 85%, whereas strain IFO 13140 produced more when fed maize glucose, producing a yield of 50% (on reducing sugars).

Topics: beta-Glucans; Polysaccharides, Bacterial; Rhizobium; Solubility; Species Specificity; Zea mays

The pathways of polysaccharide biosynthesis were investigated in cells of Sinorhizobium meliloti (strain Su47) using a stable isotope approach. The isotopic labeling of the periplasmic beta-1,2-glucans synthesized from glucose labeled at various positions evidenced the involvement of catabolic pathways, namely the pentose-phosphate and Entner-Doudoroff pathways, into the early steps of polysaccharide synthesis. The exopolysaccharides produced at the same time had a labeling pattern similar to that of the beta-glucans, indicating similar early steps for both polysaccharides. The results emphasized a cyclic organization of the carbohydrate metabolism in S. meliloti, in which the carbons of the initial hexose were allowed to re-enter the catabolic pathways many times. The metabolic incidences of such metabolic topology are discussed.

Topics: beta-Glucans; Carbohydrate Metabolism; Carbon Isotopes; Glucans; Glucose; Models, Biological; Nuclear Magnetic Resonance, Biomolecular; Pentose Phosphate Pathway; Polysaccharides, Bacterial; Sinorhizobium meliloti

During fermentation, the mutant strain Rhizobium meliloti M5N1CS, which induces nodule formation on alfalfa roots, produces a partially acetylated (1-->4)-beta-D-glucuronan. In addition to this exopolysaccharide of high molecular weight, the mutant strain produces oligoglucoronates and cyclic (1-->2)-beta-D-glucans with degrees of polymerization from 17 to 30. Under the conditions applied, magnesium has no effect on cyclic glucan production by the mutant strain, but the succinoglycan production by the wild-type strain Rhizobium meliloti M5N1 increases.

Topics: Acetylation; beta-Glucans; Chromatography, High Pressure Liquid; Culture Media; Fermentation; Glucans; Magnesium; Magnetic Resonance Spectroscopy; Polymers; Polysaccharides; Polysaccharides, Bacterial; Sinorhizobium meliloti; Species Specificity

Mutants of Rhizobium meliloti SU47 with defects in the production of the Calcofluor-binding expolysaccharide succinoglycan failed to gain entry into alfalfa root nodules. In order to define better the polysaccharide phenotypes of these exo mutants, we analyzed the periplasmic oligosaccharide cyclic (1-2)-beta-D-glucan and lipopolysaccharide (LPS) in representative mutants. The exoC mutant lacked the glucan and had abnormal LPS which appeared to lack a substantial portion of the O side chain. The exoB mutant had a spectrum of LPS species which differed from those of both the wild-type parental strain and the exoC mutant. The presence of the glucan and normal LPS in the exoA, exoD, exoF, and exoH mutants eliminated defects in these carbohydrates as explanations for the nodule entry defects of these mutants. We also assayed for high- and low-molecular-weight succinoglycans. All of the exo mutants except exoD and exoH completely lacked both forms. For the Calcofluor-dim exoD mutant, the distribution of high- and low-molecular-weight forms depended on the growth medium. The haloless exoH mutant produced high-molecular-weight and only a trace of low-molecular-weight succinoglycan; the succinyl modification was missing, as was expected from the results of previous studies. The implications of these observations with regard to nodule entry are discussed.

Topics: beta-Glucans; Chromatography, Gel; Electrophoresis, Polyacrylamide Gel; Glucans; Lipopolysaccharides; Magnetic Resonance Spectroscopy; Mutation; Polysaccharides, Bacterial; Rhizobium