Effect of oxygen tension on L-lysine, L-threonine and L-isoleucine accumulation was investigated.Sufficient supply of oxygen to satisfy the cell's oxygen demand was essential for the maximum production in each fermentation.The dissolved oxygen level must be controlled at greater than 0.01 atm in every fermentation, and the optimum redox potentials of culture media were above -170mV in L-lysine and L-threonine and above -180mV in L-isoleucine fermentations.The maximum concentrations of the products were 45.5mg/ml for L-lysine, 10.3 mg/ml for L-threonine and 15.1 mg/ml for L-isoleucine. The degree of the inhibition due to oxygen limitation was slight in the fermentative production of L-lysine, L-threonine and Lisoleucine, whose biosynthesis is initiated with L-aspartic acid, in contrast to the accumulation of L-proline, L-glutamine and L-arginine, which is biosynthesized by way of L-glutamic acid.

Acetic acid and glucose were compared in their characteristics as a substrate for L-threo nine fermentation. Maximum accumulation of threonine was 39.5 mg/ml at the yield of 15.3 when acetic acid was employed as a substrate, as compared to 10.3 mg/ml (10.0%) in glucose supplied culture. In acetate fed culture, maximum production could be obtained under oxygen limited condition at the value of Tab/KrM (rate of cell respiration/maximum rate of cell respiration) 0.35-0.45. At the rab/KrM greater than 0.5, the rate of acetate assimilation increased and homoserine accumulated as a by-product resulting in poor productivity. In

The effect of oxygen supply on L-leucine fermentation was investigated employing a leucine-producing mutant of Brevibacterium lactofermentum. Since it was not possible to measure oxygen tension below 0.01 atm by a Teflon-coated oxygen electrode, the degree of satisfaction of the cells' oxygen demand (cells' respiration rate/maximum oxygen demand of cells, rab/KrM) and the redox potential of the culture medium (E, mV) were used as indices to oxygen supply in cultures under low oxygen tension. When the oxygen demand of the cells was satisfied (rab/KrM = 1.0) and the E value was between --90 and --110mV, L-leucine formation was 26.5 mg/ml. When the oxygen demand of the cells was not satisfied (rab/KrM = 0.85) and the E value was between --200 and --220 mV, L-leucine accumulation was 29.7 mg/ml. When the oxygen supply was extremely limited (rab/KrM = 0.27) and the E value was --280 mV, L-leucine formation was 12.9 mg/ml. A new method which simultaneously measures the redox potential and dissolved oxygen was applied to the determination of the critical dissolved oxygen level for cell respiration (PL crit), whick was too small to be detected by conventional oxygen electrodes. The value of PL crit of the leucine producer was estimated as 0.0002 atm.