5-Aminolevulinic acid production in engineered Corynebacterium glutamicum via C₅ biosynthesis pathway

ALA (5-aminolevulinic acid) is an important intermediate in the synthesis of tetrapyrroles and the use of ALA has been gradually increasing in many fields, including medicine and agriculture. In this study, improved biological production of ALA in Corynebacterium glutamicum was achieved by overexpressing glutamate-initiated C₅ pathway. For this purpose, copies of the glutamyl t-RNA reductase HemA from several bacteria were mutated by site-directed mutagenesis of which a HemA version from Salmonella typhimurium exhibited the highest ALA production. Cultivation of the HemA-expressing strain produced approximately 204mg/L of ALA, while co-expression with HemL (glutamate-1-semialdehyde aminotransferase) increased ALA concentration to 457mg/L, representing 11.6- and 25.9-fold increases over the control strain (17mg/L of ALA). Further effects of metabolic perturbation were investigated, leading to penicillin addition that further improves ALA production to 584mg/L. In an optimized flask fermentation, engineered C. glutamicum strains expressing the HemA and hemAL operon produced up to 1.1 and 2.2g/L ALA, respectively, under glutamate-producing conditions. The final yields represent 10.7- and 22.0-fold increases over the control strain (0.1g/L of ALA). From these findings, ALA biosynthesis from glucose was successfully demonstrated and this study is the first to report ALA overproduction in C. glutamicum via metabolic engineering.