Ferrochelatase is the terminal enzyme in heme biosynthesis. Bacillus thuringiensis (Bt) 97-27 contains two ferrochelatases, HemH1 and HemH2, but their regulatory mechanisms and functional differences under virous environmental stimuli remain unclear. This study confirmed that the iron uptake regulator protein (Fur) bound to the promoters of hemH1 and hemH2, with Fe²⁺ or Fe³⁺ enhancing this binding. Heterologous expression of HemH1 and HemH2 in Escherichia coli showed that pEH2/BL grew better than pEH1/BL under different 2,2′-Bipyridyl, Fe²⁺, and Fe³⁺ concentrations. Under iron limitation, the heme precursor ALA production decreased significantly in both strains. The heme production of pEH2/BL decreased sharply under iron-limited conditions, while that of pEH1/BL decreased significantly under iron-rich conditions. The H₂O₂ sensitivity experiment revealed that E. coli pEH1/BL was more tolerant to H₂O₂ than pEH2/BL. In Bt, ΔhemH2 was most sensitive to H₂O₂ stress, but complementation of hemH1 or hemH2 partially restored H₂O₂ resistance, with the overexpressed strain pHH2/Bt being most tolerant. β-galactosidase assays indicated that Fur positively regulated hemH1 and negatively regulated hemH2 under normal conditions, but this regulation reversed with 2.5 mM Fe³⁺. qRT-PCR showed upregulation of genes related to heme synthesis, oxidative stress, and ferrous iron transport. This study reveals the functional differentiation of HemH1 and HemH2 under the joint regulation of Fur and environmental factors, highlighting their synergistic roles in heme synthesis, heavy metal detoxification, and oxidative stress resistance to maintain bacterial physiological homeostasis.

300 healthy Chinese perch (Siniperca chuatsi) (34.35 ± 0.47 g) were randomly divided into five groups (P1–P5) fed diets supplemented with 0, 0.2, 0.4, 0.8, and 1.6 g/kg protease for 8 weeks. Compared to P1, protease supplementation significantly up-regulated endogenous pepsinogen genes (pga1 and pgc) and down-regulated the muscle deamination gene ampd. In comparison to P1, the expression level of the hepatic gene ast increased in P2, P3, and P5, while gdh elevated in P2 and P3 (p < 0.05). Compared to P1, the expression of feeding-related gene npy decreased while pomc increased in P2; agrp increased in P3; and pomc and cart decreased in P5, resulting in significant increases in feed intake in P2, P3, and P5 (p < 0.05). Glycolytic genes (gk and pk) and lipid metabolism gene pparα were up-regulated in P2, P3 and P5, while hsl increased in P3 but decreased in P5 (p < 0.05). P5 exhibited significantly improved weight gain rate, specific growth rate, protein efficiency ratio, and protein retention rate, alongside reduced feed conversion ratio compared with P1. Therefore, dietary 1.6 g/kg protease significantly enhances growth, improves feed efficiency, stimulates pepsinogen secretion, and modulates deamination, glycolytic, and lipid metabolism genes in Siniperca chuatsi.