Induction of glucose oxidase, catalase, and lactonase in Aspergillus niger

Abstract

The induction of glucose oxidase, catalase, and lactonase activities was studied both in wild-type and in glucose oxidase regulatory and structural mutants of Aspergillus niger. The structural gene for glucose oxidase was isolated and used for Northern analysis and in transformation experiments using various gox mutations. Wild-type phenotype could be restored in the glucose oxidase-negative mutant (goxC) by transformation with the structural gene. We conclude, therefore, that the goxC marker which is located on chromosome 2 represents the structural gene of glucose oxidase. Glucose and a high oxygen level are necessary for the induction of all three enzyme activities in the wild-type strain and it was shown that both glucose and oxygen effects reflect regulation at the transcriptional level. The goxB mutation results in constitutive expression of all three activities although modulated to some extent by the carbon source. The goxE mutation only has an effect on lactonase and glucose oxidase expression and does not relieve the necessity for a high oxygen level. Catalase and lactonase could not be induced in the glucose oxidase-negative strain (goxC). Addition of H₂O₂ resulted in the induction of all three enzymes in the wild-type without glucose being present. The H₂O₂ induction is probably mediated by the goxB product. Besides the H₂O₂ induction there is still an effect of the carbon source on the induction. A model for induction of glucose oxidase, catalase, and lactonase in A. niger is discussed. Transformation of wild-type and goxC strains with the goxC gene resulted in only a 3–4 fold increase of glucose oxidase activity relative to the wild-type even though more than 25 copies of the structural gene were present. Transformation of the goxB strain gave higher activities but resulted in poor growth. Aspergillus nidulans does not have a glucose oxidase activity, but could be transformed with the A. niger goxC gene to a glucose oxidase-producing strain. Induction in these transformants was comparable to that in A. niger with respect to the carbon source dependency, but there was no oxygen dependencey of induction. The glucose oxidase produced by the A. nidulans transformants was kinetically indistinguishable from the A. niger enzyme, but it showed small differences in glycosylation pattern.