Genome Breeding of an Amino Acid-Producing Corynebacterium glutamicum Mutant

The classical strain breeding method based on random mutation and selection cannot avoid introducing detrimental or unnecessary mutations into the genome. A methodology that overcomes the limitations of the classical method is “genome breeding.” In this approach, biotechno-logically useful mutations identified through the genome analysis of classical mutants are systematically introduced into the wild-type genome in a pinpointed manner, thus allowing creation of a defined mutant that carries only useful mutations. This methodology was applied to generate an efficient L-lysine-producing mutant of Corynebacterium glutamicum. Introduction of the Val-59<-Ala mutation in the homoserine dehydrogenase gene and the Thr-311<-Ile mutation in the aspartokinase gene into the wild-type strain by allelic replacement resulted in accumulation of 8 and 55 g/L of L-lysine, respectively. The two mutations were then reconstituted on the wild-type genome, which led to a synergistic effect on production and accumulation of 75 g/L of L-lysine in a relatively short period of cultivation. The procedure and the impact of this methodology are described.