MICROBIAL PRODUCTION OF L-LYSINE

Abstract

Mutants sensitive to fairly low concentration of threonine or methionine were derived from Brevibacterium flavum No. 2247 (ATCC 14067). These mutants were classified into three by the growth inhibition by threonine or methionine; type A was inhibited only by threonine, type B only by methionine, and type C by both threonine and methionine. Further, every type of mutants was divided into two subtypes by their growth response; one whose growth was inhibited by threonine (or methionine) was to be recovered in the coexistence of methionine (or threonine), and the other could not be recovered.Among these six types of mutants, one whose growth was inhibited by either methionine or threonine but could be recovered by threonine or methionine, respectively, was found to produce much lysine. This character is similar to that of the threonine-sensitive and methionine-sensitive revertant derived from a homoserine auxotroph lacking homoserine dehydrogenase activity. Homoserine dehydrogenase level of these revertants and the above-mentioned lysine-producing mutants were similar, being about 3% of the original strain, No. 2247, but a little difference was observed in the minimal inhibiting concentration of threonine or methionine and the kind of agents diminishing the inhibition by threonine or methionine.Furthermore, about one-half of threonine auxotrophs which were derived from the above-mentioned lysine-producing mutants sensitive to either threonine or methionine were found to produce larger amounts of lysine than the above parental mutants.A modified microbiological assay procedure using lysine auxotroph was introduced to isolate non-auxotrophic lysine-producing mutants directly from No. 2247. However, no mutants other than the two known types of lysine- producer (threonine- sensitive, methionine-sensitive mutants and S-(2-aminoethyl)- L-cysteine-resistant mutants) were found through this procedure.