Production of 5-aminolevulinic Acid by Recombinant Streptomyces coelicolor Expressing hemA from Rhodobacter sphaeroides

Systematic development of a highly efficient cell factory for 5-aminolevulinic acid production

The versatile applications of 5-aminolevulinic acid (5-ALA) across the fields of agriculture, livestock, and medicine necessitate a cost-efficient biomanufacturing process. In this study, we achieved the economic viability of biomanufacturing this compound through a systematic engineering framework. First, we obtained a 5-ALA synthase (ALAS) with superior performance by exploring its natural diversity with divergent evolution. Subsequently, using a genome-scale model, we identified and modified four key targets from distinct pathways in Escherichia coli, resulting in a final enhancement of 5-ALA titers up to 21.82 g/l in a 5-l bioreactor. Furthermore, recognizing that an imbalance of redox equivalents hindered further titer improvement, we developed a dynamic control system that effectively balances redox status and carbon flux. Ultimately, we collaboratively optimized the artificial redox homeostasis system at the transcription level with other cofactors at the feeding level, demonstrating the highest recorded performance to date with a titer of 63.39 g/l for the biomanufacturing of 5-ALA.

Natural 5-Aminolevulinic Acid: Sources, Biosynthesis, Detection and Applications

5-Aminolevulinic acid (5-ALA) is the key precursor for the biosynthesis of tetrapyrrole compounds, with wide applications in medicine, agriculture and other burgeoning fields. Because of its potential applications and disadvantages of chemical synthesis, alternative biotechnological methods have drawn increasing attention. In this review, the recent progress in biosynthetic pathways and regulatory mechanisms of 5-ALA synthesis in biological hosts are summarized. The research progress on 5-ALA biosynthesis via the C4/C5 pathway in microbial cells is emphasized, and the corresponding biotechnological design strategies are highlighted and discussed in detail. In addition, the detection methods and applications of 5-ALA are also reviewed. Finally, perspectives on potential strategies for improving the biosynthesis of 5-ALA and understanding the related mechanisms to further promote its industrial application are conceived and proposed.

Challenges and opportunities of bioprocessing 5-aminolevulinic acid using genetic and metabolic engineering: a critical review

5-Aminolevulinic acid (5-ALA), a non-proteinogenic five-carbon amino acid, has received intensive attentions in medicine due to its approval by the US Food and Drug Administration (FDA) for cancer diagnosis and treatment as photodynamic therapy. As chemical synthesis of 5-ALA performed low yield, complicated processes, and high cost, biosynthesis of 5-ALA via C4 (also called Shemin pathway) and C5 pathway related to heme biosynthesis in microorganism equipped more advantages. In C4 pathway, 5-ALA is derived from condensation of succinyl-CoA and glycine by 5-aminolevulic acid synthase (ALAS) with pyridoxal phosphate (PLP) as co-factor in one-step biotransformation. The C5 pathway involves three enzymes comprising glutamyl-tRNA synthetase (GltX), glutamyl-tRNA reductase (HemA), and glutamate-1-semialdehyde aminotransferase (HemL) from α-ketoglutarate in TCA cycle to 5-ALA and heme. In this review, we describe the recent results of 5-ALA production from different genes and microorganisms via genetic and metabolic engineering approaches. The regulation of different chassis is fine-tuned by applying synthetic biology and boosts 5-ALA production eventually. The purification process, challenges, and opportunities of 5-ALA for industrial applications are also summarized.

Plasmid-Free System and Modular Design for Efficient 5-Aminolevulinic Acid Production by Engineered Escherichia coli

5-Aminolevulinic acid (ALA) is an essential intermediate for many organisms and has been considered for the applications of medical especially in photodynamic therapy of cancer recently. However, ALA production via chemical approach is complicated; hence, microbial manufacturing has received more attentions. In this study, a modular design to simultaneously express ALA synthase from Rhodobacter sphaeroides (RshemA), a non-specific ALA exporter (RhtA), and chaperones was first developed and discussed. The ALA production was significantly increased by coexpressing RhtA and RshemA. Besides, ALA was enhanced by the cofactor pyridoxal phosphate (PLP) which was supplied by expressing genes of pdxK and pdxY or direct addition. However, inclusion bodies of RshemA served as an obstacle; thus, chaperones DnaK and GroELS were introduced to reform the conformation of proteins and successfully improved ALA production. Finally, a plasmid-free strain RrGI, as the robust chassis, was established and a 6.23-fold enhancement on ALA biosynthesis and led to 7.47 g/L titer and 0.588 g/L/h productivity under the optimal cultural condition.

Strain engineering for high-level 5-aminolevulinic acid production in Escherichia coli

Herein, we report the development of a microbial bioprocess for high-level production of 5-aminolevulinic acid (5-ALA), a valuable non-proteinogenic amino acid with multiple applications in medical, agricultural, and food industries, using Escherichia coli as a cell factory. We first implemented the Shemin (i.e., C4) pathway for heterologous 5-ALA biosynthesis in E. coli. To reduce, but not to abolish, the carbon flux toward essential tetrapyrrole/porphyrin biosynthesis, we applied clustered regularly interspersed short palindromic repeats interference (CRISPRi) to repress hemB expression, leading to extracellular 5-ALA accumulation. We then applied metabolic engineering strategies to direct more dissimilated carbon flux toward the key precursor of succinyl-CoA for enhanced 5-ALA biosynthesis. Using these engineered E. coli strains for bioreactor cultivation, we successfully demonstrated high-level 5-ALA biosynthesis from glycerol (~30 g L^-1 ) under both microaerobic and aerobic conditions, achieving up to 5.95 g L^-1 (36.9% of the theoretical maximum yield) and 6.93 g L^-1 (50.9% of the theoretical maximum yield) 5-ALA, respectively. This study represents one of the most effective bio-based production of 5-ALA from a structurally unrelated carbon to date, highlighting the importance of integrated strain engineering and bioprocessing strategies to enhance bio-based production.

Enhancing Astaxanthin Biosynthesis by Rhodosporidium toruloides Mutants and Optimization of Medium Compositions Using Response Surface Methodology

Astaxanthin is a valuable carotenoid, which has been approved as a food coloring by the US Food and Drug Administration and is considered as a food dye by the European Union (European Commission). This work aimed to attain Rhodosporidium toruloides mutants for enhanced astaxanthin accumulation using ultraviolet (UV) and gamma irradiation mutagenesis. Gamma irradiation was shown to be more efficient than UV for producing astaxanthin-overproducer. Among the screened mutants, G17, a gamma-induced mutant, exhibited the highest astaxanthin production, which was significantly higher than that of the wild strain. Response surface methodology was then applied to optimize the medium compositions for maximizing astaxanthin production by the mutant G17. The optimal medium compositions for the cultivation of G17 were determined as a peptone concentration of 19.75 g/L, malt extract concentration of 13.56 g/L, and glucose concentration of 19.92 g/L, with the maximum astaxanthin yield of 3021.34 µg/L ± 16.49 µg/L. This study suggests that the R. toruloides mutant (G17) is a potential candidate for astaxanthin production.