Removal Of Feedback Inhibition Research Articles

High-yield production of L-serine from glycerol by engineered Escherichia coli.

L-Serine is widely used in pharmaceutical, food and cosmetic industries, and the direct fermentation to produce L-serine from cheap carbon sources such as glycerol is greatly desired. The production of L-serine by engineered Escherichia coli from glycerol has not been achieved so far. In this study, E. coli was engineered to efficiently produce L-serine from glycerol. To this end, three L-serine deaminase genes were deleted in turn, and all of the deletions caused the maximal accumulation of L-serine at 0.06g/L. Furthermore, removal of feedback inhibition by L-serine resulted in a titer of 1.1g/L. Additionally, adaptive laboratory evolution was employed to improve glycerol utilization in combination with the overexpression of the cysteine/acetyl serine transporter gene eamA, leading to 2.36g/L L-serine (23.6% of the theoretical yield). In 5-L bioreactor, L-serine titer could reach up to 7.53g/L from glycerol, demonstrating the potential of the established strain and bioprocess.

Systems pathway engineering of Corynebacterium crenatum for improved L-arginine production.

L-arginine is an important amino acid in food and pharmaceutical industries. Until now, the main production method of L-arginine in China is the highly polluting keratin acid hydrolysis. The industrial level L-arginine production by microbial fermentation has become an important task. In previous work, we obtained a new L-arginine producing Corynebacterium crenatum (subspecies of Corynebacterium glutamicum) through screening and mutation breeding. In this work, we performed systems pathway engineering of C. crenatum for improved L-arginine production, involving amplification of L-arginine biosynthetic pathway flux by removal of feedback inhibition and overexpression of arginine operon; optimization of NADPH supply by modulation of metabolic flux distribution between glycolysis and pentose phosphate pathway; increasing glucose consumption by strengthening the preexisting glucose transporter and exploitation of new glucose uptake system; channeling excess carbon flux from glycolysis into tricarboxylic acid cycle to alleviate the glucose overflow metabolism; redistribution of carbon flux at α-ketoglutarate metabolic node to channel more flux into L-arginine biosynthetic pathway; minimization of carbon and cofactor loss by attenuation of byproducts formation. The final strain could produce 87.3 g L−1 L-arginine with yield up to 0.431 g L-arginine g−1 glucose in fed-batch fermentation.

Engineering of an Escherichia coli Strain for the Production of 3-Methyl-1-Butanol

3-Methyl-1-butanol is a potential fuel additive or substitute. Previously this compound was identified in small quantities in yeast fermentation as one of the fusel alcohols. In this work, we engineered an Escherichia coli strain to produce 3-methyl-1-butanol from glucose via the host's amino acid biosynthetic pathways. Strain improvement with the removal of feedback inhibition and competing pathways increased the selectivity and productivity of 3-methyl-1-butanol. This work demonstrates the feasibility of production of 3-methyl-1-butanol as a biofuel and shows promise in using E. coli as a host for production.