Direct methods for selecting mutants with increased production of invertase from mutagenized cultures ofAspergillus fumigatus

Abstract

Aspergillus fumigatus 1, the most effective strain for production of invertase was selected out of moulds and yeast belonging to different species by the method of test-tube microculture. Conidia of the selected strain were further subjected to mutagenesis with both U.V. and N-methyl-N'-nitro-N-nitrosoguanidine (NTG), and the products were analysed for invertase activity with our own diffusion plate method. As a result of mutagenization and selection to obtain biochemical mutants (e.g. resistant to some metabolic inhibitors, surviving conditions of certain stresses, poorly growing on minimal medium containing glycerol or mannose), the Aspergillus fumigatus strains were obtained. Ten of these mutants showed an increased extracellular invertase, the level of which ranged widely for indi-vidual cases from 23.1 to over 96% in comparison with the parental strain. The studies of the relation-ship between a criterion of selection and frequency of mutation showed that the highest frequency of positive mutations was obtained with regard to mutants resistant to phosphomycin (58%) and 2-deoxy-D-glucose (53%). The time course of growth and enzyme production by the most active mutant M-7 showed intra- and extracellular invertase activities to have increased about 2-fold, com-pared with the parental strain.