Characterization of an Isoamylase-hyperproducing Mutant of Pseudomonas amyloderamosa

Abstract

An isoamylase-hyperproducing mutant, strain MI-414, was isolated by treating Pseudomonas amyloderamosa SB-15 with N-methyl-N'-nitro-N-nitrosoguanidine. Strain MI-414 produced 10-fold more isoamylase than strain SB-15. SI nuclease mapping of isoamylase mRNAs from the strains showed that the level of isoamylase mRNA was higher in MI-414 than in SB-15. The copy number of the isoamylase gene (iam) was not changed by the mutation. Moreover, the nucleotide sequence of the promoter region of iam, the transcription initiation site, and the expression patterns of iam in the presence of glucose and of maltose were the same in these strains. However, the half-lives of iam-mRNAs in SB-15 and MI-414 were approximately 3 and 22min, respectively. Therefore, hyperproduction of isoamylase in the mutant results, at least partly, from the greater stability of its mRNA.