Microbial Synthesis of Heme b: Biosynthetic Pathways, Current Strategies, Detection, and Future Prospects

Multi-modular metabolic engineering of heme synthesis in Corynebacterium glutamicum

Heme, an iron-containing porphyrin derivative, holds great promise in fields like medicine, food production and chemicals. Here, we developed an engineered Corynebacterium glutamicum strain for efficient heme production by combining modular engineering and RBS engineering. The whole heme biosynthetic pathway was methodically divided into 5-ALA synthetic module, uroporphyrinogen III (UPG III) synthetic module and heme synthetic module for further construction and optimization. Three heme synthetic modules were compared and the siroheme-dependent (SHD) pathway was identified to be optimal in C. glutamicum for the first time. To further improve heme production, the expression of genes in UPG III synthetic module and heme synthetic module was coordinated optimized through RBS engineering, respectively. Subsequently, heme oxygenase was knocked out to reduce heme degradation. The engineered strain HS12 showed a maximum iron-containing porphyrin derivatives titer of 1592 mg/L with the extracellular secretion rate of 45.5% in fed-batch fermentation. Our study constructed a C. glutamicum chassis strain for efficient heme accumulation, which was beneficial for the advancement of efficient heme and other porphyrins production.

A comprehensive review on the recent advances for 5-aminolevulinic acid production by the engineered bacteria

5-Aminolevulinic acid (5-ALA) is a non-proteinogenic amino acid essential for synthesizing tetrapyrrole compounds, including heme, chlorophyll, cytochrome, and vitamin B12. As a plant growth regulator, 5-ALA is extensively used in agriculture to enhance crop yield and quality. The complexity and low yield of chemical synthesis methods have led to significant interest in the microbial synthesis of 5-ALA. Advanced strategies, including the: enhancement of precursor and cofactor supply, compartmentalization of key enzymes, product transporters engineering, by-product formation reduction, and biosensor-based dynamic regulation, have been implemented in bacteria for 5-ALA production, significantly advancing its industrialization. This article offers a comprehensive review of recent developments in 5-ALA production using engineered bacteria and presents new insights to propel the field forward.

Biosynthesis, acquisition, regulation, and upcycling of heme: recent advances

Heme, an iron-containing tetrapyrrole in hemoproteins, including: hemoglobin, myoglobin, catalase, cytochrome c, and cytochrome P450, plays critical physiological roles in different organisms. Heme-derived chemicals, such as biliverdin, bilirubin, and phycocyanobilin, are known for their antioxidant and anti-inflammatory properties and have shown great potential in fighting viruses and diseases. Therefore, more and more attention has been paid to the biosynthesis of hemoproteins and heme derivatives, which depends on the adequate heme supply in various microbial cell factories. The enhancement of endogenous biosynthesis and exogenous uptake can improve the intracellular heme supply, but the excess free heme is toxic to the cells. Therefore, based on the heme-responsive regulators, several sensitive biosensors were developed to fine-tune the intracellular levels of heme. In this review, recent advances in the: biosynthesis, acquisition, regulation, and upcycling of heme were summarized to provide a solid foundation for the efficient production and application of high-value-added hemoproteins and heme derivatives.