Reduced nicotinamide adenine nucleotide phosphate (NADPH), which is one of the key cofactors in the metabolic network, plays an important role in the biochemical reactions, and physiological function of amino acid-producing strains. The manipulation of NADPH availability and form is an efficient and easy method of redirecting the carbon flux to the amino acid biosynthesis in industrial strains. In this review, we survey the metabolic mode of NADPH. Furthermore, we summarize the research developments in the understanding of the relationship between NADPH metabolism and amino acid biosynthesis. Detailed strategies to manipulate NADPH availability are addressed based on this knowledge. Finally, the uses of NADPH manipulation strategies to enhance the metabolic function of amino acid-producing strains are discussed.

Antisense RNA molecule represents a unique type of DNA transcript that comprises 19–23 nucleotides and is complementary to mRNA. Antisense RNAs play the crucial role in regulating gene expression at...

Oxaloacetate (OAA) and l-glutamate are essential precursors for the biosynthesis of l-lysine. Reasonable control of all potentially rate-limiting steps, including the precursors supply rate, is of vital importance to maximize the efficiency of l-lysine fermentation process. In this paper, we have rationally engineered the tricarboxylic acid (TCA) cycle that increased the carbon yield (from 36.18 to 59.65%), final titer (from 14.47 ± 0.41 to 23.86 ± 2.16 g L−1) and productivity (from 0.30 to 0.50 g L−1 h−1) of l-lysine by Corynebacterium glutamicum in shake-flask fermentation because of improving the OAA and l-glutamate availability. To do this, the phosphoenolpyruvate–pyruvate–oxaloacetate (PEP–pyruvate–OAA) node’s genes ppc and pyc were inserted in the genes pck and odx loci, the P1 promoter of the TCA cycle’s gene gltA was deleted, and the nature promoter of glutamate dehydrogenase-coding gene gdh was replaced by Ptac-M promoter that resulted in the final engineered strain C. glutamicum JL-69Ptac-M gdh. Furthermore, the suitable addition of biotin accelerates the l-lysine production in strain JL-69Ptac-M gdh because it elastically adjusts the carbon flux for cell growth and precursor supply. The final strain JL-69Ptac-M gdh could produce 181.5 ± 11.74 g L−1 of l-lysine with a productivity of 3.78 g L−1 h−1 and maximal specific production rate (qLys, max.) of 0.73 ± 0.16 g g−1 h−1 in fed-batch culture during adding 2.4 mg L−1 biotin with four times. Our results reveal that sufficient biomass, OAA and l-glutamate are equally important in the development of l-lysine high-yielding strain, and it is the first time to verify that fed-batch biotin plays a positive role in improving l-lysine production.

L-Leucine, as an essential branched-chain amino acid for humans and animals, has recently been attracting much attention because of its potential for a fast-growing market demand. The applicability ranges from flavor enhancers, animal feed additives and ingredients in cosmetic to specialty nutrients in pharmaceutical and medical fields. Microbial fermentation is the major method for producing l-leucine by using Escherichia coli and Corynebacterium glutamicum as host bacteria. This review gives an overview of the metabolic pathway of l-leucine (i.e. production, import and export systems) and highlights the main regulatory mechanisms of operons in E. coli and C. glutamicum l-leucine biosynthesis. We summarize here the current trends in metabolic engineering techniques and strategies for manipulating l-leucine producing strains. Finally, future perspectives to construct industrially advantageous strains are considered with respect to recent advances in biology.

The efficiency of industrial fermentation process mainly depends on carbon yield, final titer and productivity. To improve the efficiency of l-lysine production from mixed sugar, we engineered carbohydrate metabolism systems to enhance the effective use of sugar in this study. A functional metabolic pathway of sucrose and fructose was engineered through introduction of fructokinase from Clostridium acetobutylicum. l-lysine production was further increased through replacement of phosphoenolpyruvate-dependent glucose and fructose uptake system (PTS^Glc and PTS^Fru) by inositol permeases (IolT1 and IolT2) and ATP-dependent glucokinase (ATP-GlK). However, the shortage of intracellular ATP has a significantly negative impact on sugar consumption rate, cell growth and l-lysine production. To overcome this defect, the recombinant strain was modified to co-express bifunctional ADP-dependent glucokinase (ADP-GlK/PFK) and NADH dehydrogenase (NDH-2) as well as to inactivate SigmaH factor (SigH), thus reducing the consumption of ATP and increasing ATP regeneration. Combination of these genetic modifications resulted in an engineered C. glutamicum strain K-8 capable of producing 221.3 ± 17.6 g/L l-lysine with productivity of 5.53 g/L/h and carbon yield of 0.71 g/g glucose in fed-batch fermentation. As far as we know, this is the best efficiency of l-lysine production from mixed sugar. This is also the first report for improving the efficiency of l-lysine production by systematic modification of carbohydrate metabolism systems.