Abstract
L-ornithine, a valuable non-protein amino acid, has a wide range of applications in the pharmaceutical and food industries. Currently, microbial fermentation is a promising, sustainable, and environment-friendly method to produce L-ornithine. However, the industrial production capacity of L-ornithine by microbial fermentation is low and rarely meets the market demands. Various strategies have been employed to improve the L-ornithine production titers in the model strain, Corynebacterium glutamicum, which serves as a major indicator for improving the cost-effectiveness of L-ornithine production by microbial fermentation. This review focuses on the development of high L-ornithine-producing strains by metabolic engineering and reviews the recent advances in breeding strategies, such as reducing by-product formation, improving the supplementation of precursor glutamate, releasing negative regulation and negative feedback inhibition, increasing the supply of intracellular cofactors, modulating the central metabolic pathway, enhancing the transport system, and adaptive evolution for improving L-ornithine production.
Highlights
The amino acid market is worth several billion dollars
The yield of L-ornithine did not improve further upon overexpression of the argCJBD operon by employing a plasmid or by inserting a strong promoter as the ArgR repressor was absent (Zhang B. et al, 2017; Zhang et al, 2018a). This suggested that the production of L-ornithine limited by the low expression of the argCJBD operon can be addressed by removing the ArgR repressor, which concurred with the results described in the construction of the L-arginine-producing strain (Chen et al, 2014; Park et al, 2014)
Several comprehensive and rational genetic strategies have been employed for engineering C. glutamicum strains to produce L-ornithine
Summary
The amino acid market is worth several billion dollars. the production of amino acids has been an active field of biotechnology research in recent years (Lee and Wendisch, 2017; Li et al, 2017; D’Este et al, 2018). The proB/NCgl2274 (encodes γ-glutamyl kinase) gene has been deleted to construct high L-ornithine-producing strains by blocking the L-proline biosynthetic pathway.
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