Selection of biochemical mutants of Aspergillus niger resistant to some abiotic stresses with increased inulinase production.

Abstract

The present work aimed at evaluating the usefulness of selecting different kinds of biochemical mutants of Aspergillus niger to increase inulinase production in submerged culture. Conidia of A. niger 13/36, an active producer of inulinase, were subjected to mutagenesis with both u.v. and N-methyl-N'-nitro-N-nitrosoguanidine (NTG), and the products were analysed for inulinase activity with our own diffusion plate method. As a result of mutagenization and selection for obtaining biochemical mutants (e.g. surviving conditions of certain abiotic stresses, good growing on basal medium at 15 and 40 degrees C), A. niger strains resistant to these agents were obtained. Studies of the relationship between a criterion of selection and the frequency of mutation showed that the highest frequency of positive mutations in the second selection (86%) was obtained in mutants characteristic of the best growth at the low temperature (15 degrees C), when compared with the parent culture (28%). The most active mutants grown under stress conditions showed significantly higher inulinase activity (about 1.2-4.5-fold), when compared with the parent strain. The studies presented seem to confirm a high effectiveness of selection in some kinds of biochemical mutants of A. niger with regard to increased inulinase activity. This screening strategy of mutants can be a contribution to modern commercial enzyme production.