Isolation and Properties of Threonine-producing Mutants with both Dihydrodipicolinate Synthase Defect and Feedback-resistant Homoserine Dehydrogenase from Brevibacterium flavum(Microbiology & Fermentation Industry)

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Threonine-producing mutants of Brevibacterium flavum with HDR or DPS defect were selected by resistance to less than 8 g/l of AHV, a threonine analogue, in our previous studies. Growth of a mutant with HD^R, BK 29, was still inhibited by 12 g/l of AHV. Eighteen AHV-resistant mutants derived from strain BK29 under these conditions produced more than 12 g/l of threonine. AH the best five strains tested showed much lower levels of or no DPS activity in addition to HD^R. The best threonine producer, strain DB185, produced 16.5 g/l of L-threonine, about twice that by the parent, but the accumulation of lysine decreased to 3.8 from 10 g/l as the HCl salt by the parent. The threonine production and growth were stimulated by DAP. On the other hand, growth of a mutant with DPS defect, DK330, was not inhibited by 12 g/l of AHV. However, addition of lysine enhanced the growth inhibition by AHV to be almost as complete as that of strain BK29. The best strain BD122 among mutants resistant to AHV plus lysine derived from strain DK330 produced 16.6 g/l of L-threonine, while the parent produced 11.2 g/l. Both HD and AK of the mutant showed normal sensitivities to feedback inhibition, but its HK activity increased 2.1-fold over that of the parent.
社団法人日本農芸化学会の論文
1990-06-23