Production of L-Threonine by Mutants Resistant to Both α-Amino-β-hydroxyvaleric Acid and S-(2-Aminoethyl)-L-cysteine Derived from Brevibacterium flavum

Abstract

Growth of Brevibacterium flavum FA-1-30 and FA-3-115, L-lysine producers derived from Br. flavum No. 2247 as S-(2-aminoethyl)-L-cysteine (AEC) resistant mutants, was inhibited by α-amino-β-hydroxyvaleric acid (AHV), and this inhibition was reversed by L-threonine. All the tested AHV resistant mutants derived from FA-1-30 accumulated more than 4g/liter of L-threonine in media containing 10% glucose, and the best producer, FAB-44, selected on a medium containing 5mg/ml of AHV produced about 15g/liter of L-threonine. Many of AHV resistant mutants selected on a medium containing 2mg/ml of AHV accumulated L-lysine as well as L-threonine. AHV resistant mutants derived from FA-3-115 produced 10.7g/liter of L-threonine maximally. AEC resistant mutants derived from strains BB-82 and BB-69, which were L-threonine producers derived from Br. fiavum No. 2247 as AHV resistant mutants, did not produce L-threonine more than the parental strains, and moreover, many of them did not accumulate L-threonine but L-lysine. Homoserine dehydrogenases of crude extracts from L-threonine producing ARV resistant mutants derived from FA-1-30 and FA-3-115 were insensitive to the inhibition by L-threonine, and those of L-threonine and L-lysine producing AHV resistant mutants from FA-1-30 were partially sensitive.
Correlation between L-threonine or L-lysine production and regulations of enzymatic activities of the mutants was discussed.