Characterization of mutations induced by N-methyl-N′-nitro-N-nitrosoguanidine in an industrial Corynebacterium glutamicum strain

Mutations induced by classical whole-cell mutagenesis using N-methyl-N′-nitro-N-nitrosoguanidine (NTG) were determined for all genes of pathways from glucose to l-lysine in an industrial l-lysine producer of Corynebacterium glutamicum. A total of 50 mutations with a genome-wide distribution were identified and characterized for mutational types and mutagenic specificities. Those mutations were all point mutations with single-base substitutions and no deletions, frame shifts, and insertions were found. Among six possible types of base substitutions, the mutations consisted of only two types: 47 G·C → A·T transitions and three A·T → G·C transitions with no transversion. The findings indicate a limited repertoire of amino acid substitutions by classical NTG mutagenesis and thus raise a new possibility of further improving industrial strains by optimizing key mutations through PCR-mediated site-directed mutagenesis.