Abstract
Hemoglobins (Hb) and myoglobins (Mb) are important hemoproteins with broad applications in food and medicine. Microbial cell factory is a promising approach for the green and sustainable production of hemoproteins. However, current microbial hosts face the challenges of safety and insufficient heme supply. Here, we report a global regulation strategy, "push-restrain-pull-block," to enhance heme supply for producing various active Hb and Mb in food-grade Bacillus subtilis. Initially, the insufficient supply of the precursor 5-aminolevulinate was overcome by relieving feedback inhibition and mitigating the negative effects of HemX on HemA. Next, HemD was identified as the primary uroporphyrinogen III synthase and self-assembled with HemC to minimize the formation of the uroporphyrinogen I by-product. Additionally, the coproporphyrin-dependent pathway was selected as the superior downstream route for heme synthesis, and crucial rate-limiting steps were subsequently enhanced. Moreover, heme consumption was blocked by eliminating protoheme IX farnesyltransferase. Finally, through the combination and fine-tuned expression of key genes, a 221-fold improvement of heme supply was achieved in the engineered strain. Using this stable prokaryotic chassis, we achieved production of 0.81, 0.82, 1.11, and 1.01 g L(-1) of soybean Hb, clover Hb (C-Hb), bovine Mb (B-Mb), and porcine Mb, respectively, through fermentation, marking the highest reported titers in prokaryotic systems. These hemoproteins exhibit properties similar to natural standards. Furthermore, the synthesized C-Hb and B-Mb demonstrated superior effects for preparing plant-based meat analogs as colorants and flavoring agents. This work provides a universal platform for producing other high-value hemoproteins, promising future advancements in food processing and biocatalysis.