Ultraviolet-irradiation induced and spontaneous mutation of Rhizobium trifolii 11B in relation to water-soluble and water-insoluble polysaccharide production ability

Rhizobium trifolii 11B was u.v. irradiated and nine u.v. mutants have been isolated. Among the mutants, only one, R. trifolii 21M11B, produced more (752 mg/100 ml) water-soluble polysaccharide than the parent (704 mg/100 ml). The composition of water-soluble polysaccharide from u.v. mutants differed from that of the parent, R. trifolii 11B, and none of its u.v. mutants produced water-insoluble polysaccharide as detected by the Aniline Blue method. Storage of u.v. mutants for 2 months at 5°C gave four spontaneous variants which acquired the ability to produce water-insoluble polysaccharide. The spontaneous mutants also retained their water-soluble polysaccharide producing ability. The water-soluble polysaccharide produced by these mutants was characterized as curdlan type. The chemistry of water-soluble and water-insoluble polysaccharides was also ascertained.