title: Metabolic engineering Corynebacterium glutamicum for the L-lysine production by increasing the flux into L-lysine biosynthetic pathway.
abstract: The experiments presented here were based on the conclusions of our previous results. In order to avoid introduction of expression plasmid and to balance the NADH/NAD ratio, the NADH biosynthetic enzyme, i.e., NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (GADPH), was replaced by NADP-dependent GADPH, which was used to biosynthesize NADPH rather than NADH. The results indicated that the NADH/NAD ratio significantly decreased, and glucose consumption and L-lysine production drastically improved. Moreover, increasing the flux through L-lysine biosynthetic pathway and disruption of ilvN and hom, which involve in the branched amino acid and L-methionine biosynthesis, further improved L-lysine production by Corynebacterium glutamicum. Compared to the original strain C. glutamicum Lys5, the L-lysine production and glucose conversion efficiency (α) were enhanced to 81.0 ± 6.59 mM and 36.45% by the resulting strain C. glutamicum Lys5-8 in shake flask. In addition, the by-products (i.e., L-threonine, L-methionine and L-valine) were significantly decreased as results of genetic modification in homoserine dehydrogenase (HSD) and acetohydroxyacid synthase (AHAS). In fed-batch fermentation, C. glutamicum Lys5-8 began to produce L-lysine at post-exponential growth phase and continuously increased over 36 h to a final titer of 896 ± 33.41 mM. The L-lysine productivity was 2.73 g l(-1) h(-1) and the α was 47.06% after 48 h. However, the attenuation of MurE was not beneficial to increase the L-lysine production because of decreasing the cell growth. Based on the above-mentioned results, we get the following conclusions: cofactor NADPH, precursor, the flux through L-lysine biosynthetic pathway and DCW are beneficial to improve L-lysine production in C. glutamicum.
authors.affiliation: The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800# Lihu Road, WuXi, 214122, People's Republic of China.
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Xu
authors.forename: Mei
authors.initials: M
authors.lastname: Han
authors.forename: Junlan
authors.initials: J
authors.lastname: Zhang
authors.forename: Yanfeng
authors.initials: Y
authors.lastname: Guo
authors.forename: Weiguo
authors.initials: W
authors.lastname: Zhang
mesh_terms: D048230:Corynebacterium glutamicum / Q000235:genetics / Q000378:metabolism; D008239:Lysine / Q000096:biosynthesis / Q000235:genetics; D060847:Metabolic Engineering; D009243:NAD / Q000235:genetics / Q000378:metabolism
chemical_list: D009243:NAD; D008239:Lysine