L-Lysine

Optimizing Escherichia coli strains and fermentation processes for enhanced L-lysine production: a review

lysine is an essential amino acid with significant importance, widely used in the food, feed, and pharmaceutical industries. To meet the increasing demand, microbial fermentation has emerged as an effective and sustainable method for L-lysine production. Escherichia coli has become one of the primary microorganisms for industrial L-lysine production due to its rapid growth, ease of genetic manipulation, and high production efficiency. This paper reviews the recent advances in E. coli strain engineering and fermentation process optimization for L-lysine production. Additionally, it discusses potential technological breakthroughs and challenges in E. coli-based L-lysine production, offering directions for future research to support industrial-scale production.

Sustainable Production of N-methylphenylalanine by Reductive Methylamination of Phenylpyruvate Using Engineered Corynebacterium glutamicum

N-alkylated amino acids occur widely in nature and can also be found in bioactive secondary metabolites such as the glycopeptide antibiotic vancomycin and the immunosuppressant cyclosporine A. To meet the demand for N-alkylated amino acids, they are currently produced chemically; however, these approaches often lack enantiopurity, show low product yields and require toxic reagents. Fermentative routes to N-alkylated amino acids like N-methyl-l-alanine or N-methylantranilate, a precursor of acridone alkaloids, have been established using engineered Corynebacterium glutamicum, which has been used for the industrial production of amino acids for decades. Here, we describe metabolic engineering of C. glutamicum for de novo production of N-methylphenylalanine based on reductive methylamination of phenylpyruvate. Pseudomonas putida Δ-1-piperideine-2-carboxylate reductase DpkA containing the amino acid exchanges P262A and M141L showed comparable catalytic efficiencies with phenylpyruvate and pyruvate, whereas the wild-type enzyme preferred the latter substrate over the former. Deletion of the anthranilate synthase genes trpEG and of the genes encoding branched-chain amino acid aminotransferase IlvE and phenylalanine aminotransferase AroT in a strain engineered to overproduce anthranilate abolished biosynthesis of l-tryptophan and l-phenylalanine to accumulate phenylpyruvate. Upon heterologous expression of DpkA^P262A,M141L, N-methylphenylalanine production resulted upon addition of monomethylamine to the medium. In glucose-based minimal medium, an N-methylphenylalanine titer of 0.73 ± 0.05 g L⁻¹, a volumetric productivity of 0.01 g L⁻¹ h⁻¹ and a yield of 0.052 g g⁻¹ glucose were reached. When xylose isomerase gene xylA from Xanthomonas campestris and the endogenous xylulokinase gene xylB were expressed in addition, xylose as sole carbon source supported production of N-methylphenylalanine to a titer of 0.6 ± 0.04 g L⁻¹ with a volumetric productivity of 0.008 g L⁻¹ h⁻¹ and a yield of 0.05 g g⁻¹ xylose. Thus, a fermentative route to sustainable production of N-methylphenylalanine by recombinant C. glutamicum has been established.

Improved Astaxanthin Production with Corynebacterium glutamicum by Application of a Membrane Fusion Protein

Astaxanthin is one of the strongest natural antioxidants and a red pigment occurring in nature. This C40 carotenoid is used in a broad range of applications such as a colorant in the feed industry, an antioxidant in cosmetics or as a supplement in human nutrition. Natural astaxanthin is on the rise and, hence, alternative production systems are needed. The natural carotenoid producer Corynebacterium glutamicum is a potent host for industrial fermentations, such as million-ton scale amino acid production. In C. glutamicum, astaxanthin production was established through heterologous overproduction of the cytosolic lycopene cyclase CrtY and the membrane-bound β-carotene hydroxylase and ketolase, CrtZ and CrtW, in previous studies. In this work, further metabolic engineering strategies revealed that the potential of this GRAS organism for astaxanthin production is not fully exploited yet. It was shown that the construction of a fusion protein comprising the membrane-bound β-carotene hydroxylase and ketolase (CrtZ~W) significantly increased astaxanthin production under high glucose concentration. An evaluation of used carbon sources indicated that a combination of glucose and acetate facilitated astaxanthin production. Moreover, additional overproduction of cytosolic carotenogenic enzymes increased the production of this high value compound. Taken together, a seven-fold improvement of astaxanthin production was achieved with 3.1 mg/g CDW of astaxanthin.