PRODUCTION, SELECTION, AND CHARACTERISTICS OF MUTANTS OF LEUCONOSTOC-MESENTEROIDES B-742 CONSTITUTIVE FOR DEXTRANSUCRASES

Leuconostoc mesenteroides B-742 produces Two dextransucrases on sucrose medium that synthesize a dextran containing (alpha 1-4 branch linkages and a dextran with a high degree of single ct 1-3-linked branched glucose residues. We performed mutagenesis on the parent strain with ethyl methane sulfonate and isolated mutants that are constitutive for dextransucrases. These dextransucrases synthesized dextrans that had different properties. The mutants produced extracellular dextransucrases on glucose with higher activities (2.5-11 times) than what the parent strain produced on sucrose. Based on the Penicillium endo-dextranase hydrolysis, mutant B-742C dextransucrases produced different dextrans when they were prepared from glucose and sucrose. Mutant B-742CA dextransucrase prepared from glucose and sucrose formed the same dextran. Mutant B-742CB dextransucrase, prepared from glucose and sucrose, also formed the same dextran; however, the dextran was different from that of B-742CA. Differences in physical appearence, solubility, and susceptibility to endo-dextranase hydrolysis of the dextrans prepared by different mutants grown on glucose and sucrose were found. Mutant B-742C appeared to elaborate on sucrose medium two dextransucrases that synthesized both fraction L-and fraction S-type dextrans. When grown on glucose, B-742C appeared to elaborate a dextransucrase that only synthesized fraction L-type dextran. Mutant B-742CA appeared to elaborate a dextransucrase that only synthesized fraction L-type dextran, and mutant B-742CB appeared to elaborate a dextransucrase that only synthesized fraction S-type dextran. Nondenaturing SDS-PAGE gave activity bands that had a molecular size of 184 kD for each of the dextransucrases produced by the different mutants.