Integrated Optimization of the In Vivo Heme Biosynthesis Pathway and the In Vitro Iron Concentration for 5-Aminolevulinate Production.

5-Aminolevulinic acid (ALA) is a nonprotein amino acid that has been widely used in many fields. In this study, we developed a new process for ALA production by optimizing the in vivo heme biosynthesis pathway and the iron concentration during cultivation. With the addition of iron, co-overexpression of the heme synthesis pathway genes hemA, hemL, hemF, and hemD significantly increased the accumulation of ALA and cell biomass. Further experiments demonstrated that the increased ALA accumulation resulted from moderate repression of ALA dehydratase (encoded by hemB), which was caused by hemF overexpression. After the addition of an optimized concentration (7.5 mg/L) of iron, ALA production by the recombinant Escherichia coli LADF-6 strain that overexpressed hemA, hemL, hemD, and hemF increased to 2840 mg/L in flask cultures. After applying a batch fermentation strategy, the ALA concentration increased to 4.05 g/L, with a productivity of 0.127 g/L·h. The results showed that the moderate repression of the in vivo heme pathway enzyme ALA dehydratase and the simultaneous optimization of the in vitro iron ion concentration served to increase the production of ALA and cell biomass.