Recent Advances in Bio-Based Production of Free Heme Using Microbial Metabolic Engineering

Heme is an iron-containing porphyrin that plays an indispensable role in biological system, involved in oxygen transport, electron transfer, gas sensing, enzyme catalysis, etc. Beyond its physiological functions, heme also has wide-ranging applications in pharmaceuticals, food additives, and biotechnology. However, conventional production methods-such as chemical synthesis and extraction from animal blood are hindered by high costs, ethical concerns, environmental burdens, and safety risks. Recent progresses in metabolic engineering and synthetic biology have made it possible to produce free heme using microorganisms, offering a scalable, cost-effective, and sustainable alternative. This review provides a comprehensive overview of bio-based heme production, focusing on: 1) Structure, functions, and synonyms of different heme types; 2) Conserved and divergent heme biosynthetic pathways; 3) Heme biosynthesis regulation involving transcription factors, protein interactions, and small molecules; 4) Recent advances in microbial production of heme and porphyrin intermediates using metabolic engineering strategies; 5) Methods for heme detection, including spectroscopy, chromatography, enzyme-linked immunosorbent assays (ELISA) and whole-cell biosensors. Finally, current challenges and future opportunities, highlighting microbial heme production as a transformative and sustainable strategy to meet growing global demand are discussed.