Structure and properties of the exopolysaccharides produced by Pseudomonas mutabilis T6 and P. mutabilis ATCC 31014

This paper presents a study on the purification, primary structure, and rheological properties of exopolysaccharides isolated from cultures of Pseudomonas mutabilis T6 and P. mutabilis ATCC 31014. Both polymers are exopolysaccharides of D-mannose. The mannan isolated from P. mutabilis T6 contains on average about 5% of residual β-D-glucose, in contrast to the mannan from P. mutabilis ATCC 31014, which contained only trace amounts of residual β-D-glucose (less than 1%). Based on the (13)C NMR spectra, all of the remaining carbohydrates in the exopolysaccharides occur in the form of pyranose rings. All of the mannose residues have the α configuration at the anomeric carbon atom while the glucose adopts the β configuration. The reaction of both polysaccharide hydrolysates with an optically active alcohol indicates that all of the sugar residues have the D configuration. We found that the main chain of the exopolysaccharide is composed of mannose residues connected through α-(1→6) linkages, of which a large number are substituted on O2 with D-mannose and the remaining are substituted with di- to pentasaccharide fragments. The rheological properties of the exopolysaccharide isolated from P. mutabilis T6 show that its viscosity is over 30 times greater than that of P. mutabilis ATCC 31014.