Application of Protoplast Fusion to the Development of l-Threonine and l-Lysine Producers

A method of polyethyleneglycol(PEG)-induced protoplast fusion was developed for obtaining better Brevibacterium amino acid producers. By this method, interspecific and intraspecific recombinants among mutants of Brevibacterium sp. were obtained at a frequency of 10 -3 ~ 10 -5 . In order to improve the threonine productivity, a genetic marker of lysine-requirement was introduced by protoplast fusion into a strain of B. lactofermentum that produced threonine and lysine simultaneously. The resultant lysine-requiring recombinants accumulated only threonine, with an increased yield. On the other hand, protoplast fusion was carried out to improve the glucose metabolizing activity of industrial lysine producers. The low rate of glucose consumption of a lysine producer due to multi-step breeding was improved by protoplast fusion with a strain showing rapid glucose consumption. The rate of glucose consumption of the recombinant was 3 times higher than that of the parental lysine producer, and the lysine production yield of the recombinant was the same as that of the parental strain.