MICROBIAL PRODUCTION OF L-LYSINE .2. PRODUCTION BY MUTANTS SENSITIVE TO THREONINE OR METHIONINE

Some prototrophic revertants from a homoserine auxotroph of Brevibacterium flavum No. 2247 (ATCC No. 14067), which grew as rapidly as No. 2247 in a minimal glucose-salts medium produced large amounts of lysine, whereas No. 2247, the original strain, produced little. The cell growth in a minimal medium of revertant strain, S-20, which produced 23 g of L-lysine monohydrochloride from 100 g of glucose, was completely inhibited by the addition of 10μg/ml of L-methionine (or L-threonine) and recovered by the further addition of L-threonine (or L-methionine). It was concluded that much lower homoserine dehydrogenase activity of S-20 than that of No. 2247 was the primary result of the mutation, which might cause apparent increase in the sensitivity of the cell growth to inhibition by L-methionine (or L-threonine) and further production of lysine through lowering of the threonine pool inside the cell. Some of the threonine auxotrophs derived from such revertant strains as S-20 produced much larger amounts of lysine than the parental strains or simple threonine auxotrophs directly derived from No. 2247. The amount of lysine produced was nearly equal to that of homoserine auxotroph, H-1013, derived from No. 2247. By-production of homoserine was small in contrast with the simple threonine auxotrophs as expected. These threonine auxotrophs were still sensitive to higher concentration of L-threonine. © 1969, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.