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

Programmable Bacterial Architects Crafting Sonosensitizers for Tumor-Specific Sonodynamic Immunotherapy

Sonodynamic therapy (SDT) is a non-invasive cancer treatment that uses ultrasound to activate sonosensitizers for selective tumor ablation. With its superior tissue penetration compared to photodynamic therapy, SDT demonstrates the potential to stimulate antitumor immune responses by modulating the tumor microenvironment. However, its clinical application remains limited by poor tumor specificity and suboptimal sonosensitizer accumulation, which reduces efficacy and causes off-target effects. To address these challenges, an Engineered Probiotic-based Calibrated 5-ALA Supply system (SPEC5) is developed to confer tumor selectivity for SDT. Engineered non-pathogenic E. coli with recombinant plasmids enables efficient 5-ALA biosynthesis through kinetic remodeling. Homologous tumor cell membrane cloaking further enhances tumor targeting and immune evasion. Upon intravenous injection, SPEC5 selectively colonizes in the tumor, supporting the sonosensitizer protoporphyrin IX (PpIX) in situ biosynthesis via 5-aminolevulinic acid (5-ALA) continuous supply. A hypoxia-inducible promoter regulating O-acetylserine sulfhydrylase ensures the tumor specificity of PpIX production. This system achieves robust sensitizer accumulation in tumors, enhancing SDT efficacy and inducing potent antitumor immune activation with minimal systemic toxicity. Post-treatment, the bacteria are rapidly cleared to ensure safety. This study presents a novel strategy for tumor-specific sonosensitizer supply, revolutionizing 5-ALA-based SDT and paving the way for advanced tumor-targeted therapies with enhanced immunotherapeutic outcomes.

Metabolic Regulation and Engineering Strategies of Carbon and Nitrogen Metabolism in Escherichia coli

The intricacies of carbon and nitrogen metabolism in Escherichia coli indeed present both challenges and opportunities for metabolic engineering aimed at optimizing microbial production processes. Carbon is the primary energy source and building block for biomolecules at the cellular level, while nitrogen is vital for synthesizing amino acids, nucleotides, and other nitrogen-containing compounds. This review provides a comprehensive summary of the metabolic regulation of central metabolism and outlines engineering strategies for carbon and nitrogen metabolism in E. coli. This perspective enhances our understanding of the molecular mechanisms involved and enables the development of rational metabolic engineering strategies. One key aspect of metabolic engineering consists of understanding the regulatory networks that govern these processes. Both carbon and nitrogen metabolisms are tightly regulated to ensure cellular homeostasis. By elucidating the interconnected nature of carbon and nitrogen metabolism, this review serves not just to better inform the academic community but also to stimulate advancements in biotechnological applications. Metabolic engineering in E. coli, targeting these complex networks, holds immense promise for the sustainable production of chemicals, biofuels, and pharmaceuticals.

5-Aminolevulinic Acid: from pyrrole biosynthetic precursor to multifunctional plant growth regulator

5-Aminolevulinic acid (ALA) is a non-protein δ-amino acid and an essential precursor of tetrapyrrole compound biosynthesis. Nowadays, it is a well-known natural plant growth regulator with multiple biological regulatory functions. In this review, we summarize the regulatory effects of ALA in promoting plant growth and the development of organs such as roots, stems, leaves, flowers, and fruits under normal conditions as well as stressful conditions. We emphasize the newly revealed signaling transduction and transcriptional regulatory mechanisms of ALA in maintaining root functions against abiotic stresses, improving leaf photosynthetic performance, and enhancing fruit appearance and flavor qualities as well as storage. Although most of the current reports on ALA are still apparent effect descriptions rather than mechanism explorations, studies suggest that ALA can facilitate agricultural development toward higher yield, quality, efficiency, and safety. The regulatory mechanisms of ALA at different levels need further study in the future.

Engineering Corynebacterium glutamicum for the Production of 5-Aminolevulinic Acid under Microaerobic Conditions Guided by a Genome-Scale Metabolic Network

5-Aminolevulinic acid (5-ALA) has been widely used in modern agriculture and therapy as a biostimulant, feed nutrient, and photodynamic drug. Although metabolic engineering strategies have been employed to increase the yield of 5-ALA in Corynebacterium glutamicum, the production of 5-ALA under microaerobic conditions has not been studied. In this paper, we developed, for the first time, overproducing-5-ALA Corynebacterium glutamicum strains under microaerobic conditions, guided by a genome-scale metabolic network model. The engineered strain for the C4 pathway synthesis of 5-ALA was constructed based on the Corynebacterium glutamicum genome-scale metabolic network model iCW773 under different oxygen environmental conditions. The fusion of the key enzymes SucCD and HemA effectively opened the substrate channel and improved the biosynthesis of 5-ALA. Further selection of 5-ALA synthetases alleviated the inhibitory effect of heme, which further improved the titer of 5-ALA. Combinatorial optimization of the lpd, coaA, and ppc genes was employed to enhance the supply of the precursor succinyl-CoA. Finally, a 3.8 g/L 5-ALA titer was achieved in a 5-L bioreactor at 8% dissolved oxygen. This study provides a reference for the synthesis of 5-ALA or other high value-added chemicals with succinyl-CoA as the precursor under microaerobic conditions.

A new combination approach to extracellular production of 5-aminolevulinic acid for purification and application in alleviating cadmium-induced oxidative stress in maize

5-Aminolevulinic acid (ALA) is widely applied in agriculture, animal husbandry, medicine, and often manufactured in Escherichia coli for overexpressing ALA synthase (ALAS) from α-proteobacteria. For enhancing extracellular ALA production, several approaches have been exploited. Here, we developed and identified a new combination strategy to increase ALA production in E. coli, including selection of the negatively-charged peptide tag as a C-terminal fusion partner for increasing soluble production of the ALAS codon variant from Rhodobacter sphaeroides, mutation of certain residues to increase the ALAS variant activity, optimization of the signal sequences to facilitate ALA secretion, down-regulation of the hemB to inhibit ALA transformation in one plasmid expression system, and supply of 4 mM dithiothreitol to the culture to increase cells tolerant to the oxidative stress. Under the specified cultural conditions, ALA yield was up to 3.2 g/L in flash flasks. Compared with the added cadmium-induced stress, simultaneous supply of purified ALA improved maize seedlings growth, decreased contents of malondialdehyde and hydrogen peroxide, and increased peroxidase activity, contents of chlorophylls and proline.

Metabolic Engineering of Nonmodel Yeast Issatchenkia orientalis SD108 for 5-Aminolevulinic Acid Production

Biological production of 5-aminolevulinic acid (5-ALA) has received growing attention over the years. However, there is the tradeoff between 5-ALA biosynthesis and cell growth because the fermentation broth will become acidic due to the production of 5-ALA. To address this limitation, we engineered an acid-tolerant yeast, Issatchenkia orientalis SD108, for 5-ALA production. We first discovered that the cell growth rate of I. orientalis SD108 was boosted by 5-ALA and its endogenous ALA synthetase (ALAS) showed higher activity than those homologs from other yeasts. The titer of 5-ALA was improved from 28 mg/L to 120-, 150-, and 300 mg/L, by optimizing plasmid design, overexpressing a transporter, and increasing gene copy number, respectively. After redirecting the metabolic flux using the pyruvate decarboxylase (PDC) knockout strain (SD108ΔPDC) and culturing with urea, we increased the titer of 5-ALA to 510 mg/L, a 13-fold enhancement, proving the importance of the newly identified IoALAS with higher activity and the strategic selection of nitrogen sources for knockout strains. This study demonstrates the acid-tolerant I. orientalis SD108ΔPDC has a high potential for 5-ALA production at a large scale in the future.