Biosynthesis of L-lysine and L-threonine in Brevibacterium. III. Production of L-lysine by leucine auxotrophs derived from AEC resistant mutant of Brevibacterium lactofermentum.

The effect of amino acids was examined on the production of L-lysine by AEC resistant mutant of B. lactofermentum. Among amino acids tested, only leucine showed strong specific inhibition. In order to release the production of L-lysine from this negative effect of leucine, leucine auxotrophs were derived from AEC resistant strain of B. lactofermentum. Most of these leucine auxotrophs produced larger amount of L-lysine (maximally 41mg/ml) than the parental strain which produced about 18mg/ml of L-lysine. It was confirmed that leucine auxotrophs derived from AEC resistant mutant of other glutamate producing bacteria, B. saccharolyticum and Corynebacterium glutamicum. These results suggested that leucine might directly or indirectly affect the biosynthesis of lysine. However, this increase in lysine productivity of leucine auxotrophs could not be ex-plained by the alteration of aspartokinase (EC 2. 7. 2. 4) and homoserine dehydrogenase (EC 1. 1. 1. 3). These enzymes are key enzymes in lysine and threonine biosynthesis, respectively