Garrigues C, Mercade M, Cocaign-Bousquet M, Lindley N D, Loubiere P
Centre de Bioingénierie Gilbert Durand, UMR CNRS 5504, UMR INRA 792, Institut National des Sciences Appliquées, 135 Avenue de Rangueil, F-31077 Toulouse Cedex 4, France.
Biotechnol Bioeng. 2001 Jul 20;74(2):108-15.
Two strains of Lactococcus lactis ssp. cremoris, MG 1820 and MG 1363, which differed by the presence or absence of the lactose plasmid, respectively, were cultivated in batch-mode fermentation on lactose as carbon substrate. A correlation between the rate of sugar consumption, the growth rate, and the type of metabolism was observed. The MG 1820 strain grew rapidly on lactose and homolactic fermentation occurred. The major regulating factor was the NADH/NAD(+) ratio proportional to the catabolic flux, which inhibited glyceraldehyde-3-phosphate dehydrogenase activity. This control led to an increase in metabolite concentration upstream of this enzyme, glyceraldehyde-3-phosphate and dihydroxyacetone-phosphate, and inhibition of pyruvate formate lyase activity, while lactate dehydrogenase was strongly activated by the high coenzyme ratio. The contrary was observed during growth of the MG 1363 strain. Further investigation during growth of L. lactis ssp. lactis NCDO 2118 on galactose as carbon substrate and on various culture media enabling the growth rate to proceed at various rates demonstrated that the relative flux between catabolism and anabolism was the critical regulating parameter rather than the rate of glycolysis itself. In a minimal medium, where anabolism was strongly limited, the rate of sugar consumption was reduced to a low value to avoid carbon and energy waste. Despite this low sugar consumption rate, the catabolic flux was in excess relative to the anabolic capability and the NADH/NAD+ ratio was high, typical of a situation of nonlimiting catabolism leading to a homolactic metabolism.
两种乳酸乳球菌亚种乳酸乳球菌cremoris菌株，MG 1820和MG 1363，分别因乳糖质粒的存在与否而有所不同，它们在分批式发酵中以乳糖作为碳源进行培养。观察到了糖消耗速率、生长速率和代谢类型之间的相关性。MG 1820菌株在乳糖上生长迅速，发生同型乳酸发酵。主要调节因子是与分解代谢通量成正比的NADH/NAD(+) 比率，它抑制甘油醛-3-磷酸脱氢酶的活性。这种调控导致该酶上游的代谢物浓度增加，即甘油醛-3-磷酸和磷酸二羟丙酮，并抑制丙酮酸甲酸裂解酶的活性，而乳酸脱氢酶则被高辅酶比率强烈激活。在MG 1363菌株生长过程中观察到相反的情况。在乳酸乳球菌亚种乳酸乳球菌NCDO 2118以半乳糖作为碳源并在各种能使生长速率以不同速率进行的培养基上生长的过程中进行的进一步研究表明，分解代谢和合成代谢之间的相对通量是关键调节参数，而不是糖酵解本身的速率。在一种合成代谢受到强烈限制的基本培养基中，糖消耗速率降低到很低的值以避免碳和能量的浪费。尽管糖消耗速率很低，但相对于合成代谢能力而言，分解代谢通量过高，且NADH/NAD+ 比率很高，这是导致同型乳酸代谢的非限制性分解代谢情况的典型特征。
