Impact of hemB mutations on 5-aminolevulinic acid production in Escherichia coli

Abstract

Background Microbial production of 5-aminolevulinic acid (ALA) attracts attention due to a wide range of biotechnological and medical applications of ALA, including cancer treatment and diagnosis. Various genetic engineering approaches have been employed to improve ALA production in bacterial hosts such as Escherichia coli possessing the C5 pathway. Glutamyl-tRNA reductase (GluTR) encoded by hemA, glutamate-1-semialdehyde aminotransferase (GSA-AT) encoded by hemL, and ALA dehydratase (ALAD) encoded by hemB play important roles in ALA metabolism including the C5 pathway. Attenuation of the intercellular ALAD activity, which condensates 2 molecules of ALA to synthesize porphobilinogen (PBG), has been employed by various measures. However, a mutation approach by substituting catalytically important residues in ALAD encoded by hemB has never been attempted. The aim of this study is to assess the impact of hemB mutations on the ALA production in E. coli. Methods In this study, the authors mutated the amino acid residues potentially related to the enzymatic activity of E. coli ALAD by referring to a mutation experiment of human ALAD. The authors created five types of mutated hemB genes, introduced these genes to the hemB-deleted mutant strain of E. coli, and assessed the impact of the ALAD mutations on ALA production. In addition, hemA, hemL, and rhtA encoding an ALA exporter were introduced to the E. coli possessing a mutated hemB. Results The authors revealed that the mutations of ALAD employed in this study did not significantly enhance ALA production. Overexpression of hemA, hemL, and rhtA substantially increased ALA production in any E. coli strain possessing mutated hemB, while a difference in ALA production of the strain could be rather attributed to its growth behaviour than ALAD inactivation. Conclusions This study provides an important piece of information to design the bioprocess of ALA production using E. coli engineered through the C5 pathway.