Special bacterial polysaccharides and polysaccharases

Alcaligenes faecalis var. myxogenes 10C3, which we isolated from soil, produces a water-soluble and an insoluble extracellular polysaccharide. The former (succinoglycan) is composed of glucose, galactose, pyruvic acid and succinic acid (molar proportions 7:1:1:1) with (beta 1-3)-, (beta 1-4)- and (beta 1-6)-glucosidic linkages. The latter (curdlan) is composed entirely of (beta 1-3)-linked D-glucose and forms a resilient firm gel when heated in suspension. The organism also produces extracellularly a repeating-unit octasaccharide of succinoglycan and cyclic (beta 1-2)-D-glucan. These polymers or oligomers are also produced by many strains of Agrobacterium and Rhizobium. Spontaneous mutation in ability to produce these polysaccharides or oligosaccharides occurs in these strains. The structures of succinoglycan, and similar polymers containing riburonic acid or galactose as the end residue of the side chain, were elucidated by successive fragmentation with two special enzymes obtained from Cytophaga arvensicola followed by methylation analysis. It is interesting that the unit compound in the biosynthesis of succinoglycan is identical with the unit compound in the enzymic decomposition of the polymer. Studies on curdlan gel by X-ray, 13C n.m.r. and electron-microscopic analysis and other physicochemical methods showed that the molecular structure of curdlan changes from a single helix to a triple stranded helix on heat treatment at high temperature. Curdlan seems to be useful for making new types of jelly products and may also be useful in new procedures for food production. Interestingly, curdlan possesses marked antitumour activity. Extracellular isoamylase (EC 3.2.1.68; glycogen 6-glucanohydrolase) of Pseudomonas amyloderamosa SB 15, which we isolated from soil, is very useful for elucidation of the structure of amylopectin and glycogen, and also for the commercial production of amylose or maltose alone or in combination with beta-amylase. Maltose is useful as a sugar for injection, being better than glucose. Maltitol is easily produced from maltose by chemical reduction and is used as a low-calorie sweetener. The isoamylase is also effective for enhancing the production of glucose from starch by the action of glucoamylase.