Sahm H, Eggeling L, Eikmanns B, Krämer R
Institut für Biotechnologie Forschungszentrum Jülich GmbH, Germany.
Ann N Y Acad Sci. 1996 May 15;782:25-39. doi: 10.1111/j.1749-6632.1996.tb40544.x.
The gram-negative bacterium Corynebacterium glutamicum is used for the industrial production of amino acids, for example, of L-glutamate and L-lysine. By cloning and expressing the various genes of the L-lysine pathway in C. glutamicum, we would demonstrate that an increase of the flux of L-aspartate semialdehyde to L-lysine could be obtained in strains with increased dihydrodipicolinate synthase activity. Recently we detected that in C. glutamicum two pathways exist for synthesis of D,L-diaminopimelate and L-lysine. Mutants defective in one pathway are still able to synthesize enough L-lysine for growth, but the L-lysine secretion is reduced to 50 to 70%. Using NMR spectroscopy, we could calculate how much of the L-lysine secreted into the medium is synthesized via either one or the other pathway. Amplification of the feedback inhibition insensitive homoserine dehydrogenase and homoserine kinase in a high L-lysine-overproducing strain enabled channeling of the carbon flow from the intermediate aspartate semialdehyde towards homoserine, resulting in a high accumulation of L-threonine. For a further flux from L-threonine to L-isoleucine, the allosteric control of threonine dehydratase was eliminated.
革兰氏阴性菌谷氨酸棒杆菌被用于氨基酸的工业化生产，例如L-谷氨酸和L-赖氨酸。通过在谷氨酸棒杆菌中克隆和表达L-赖氨酸途径的各种基因，我们证明了在二氢吡啶二羧酸合酶活性增加的菌株中，L-天冬氨酸半醛向L-赖氨酸的通量可以增加。最近我们检测到，在谷氨酸棒杆菌中存在两条合成D，L-二氨基庚二酸和L-赖氨酸的途径。一条途径有缺陷的突变体仍然能够合成足够生长所需的L-赖氨酸，但L-赖氨酸的分泌减少到50%至70%。利用核磁共振光谱，我们可以计算出分泌到培养基中的L-赖氨酸中有多少是通过这两条途径之一合成的。在一个高产L-赖氨酸的菌株中，对反馈抑制不敏感的高丝氨酸脱氢酶和高丝氨酸激酶的扩增使得碳流从中间产物天冬氨酸半醛流向高丝氨酸，导致L-苏氨酸的大量积累。为了使L-苏氨酸进一步转化为L-异亮氨酸，消除了苏氨酸脱水酶的别构控制。
