Precise flux redistribution to glyoxylate cycle for 5-aminolevulinic acid production in Escherichia coli.

Microbial production of 5-aminolevulinic acid (ALA) has received much attention because of its potential in clinical applications. Overexpression along with the deciphering of regulation of the related enzymes and an analogue transporter yielded remarkable achievements in ALA production. Nonetheless, there is significant room for carbon flux optimization to enhance ALA production. The aim of this study was precise carbon flux optimization for high ALA production in Escherichia coli expressing the ALA biosynthetic pathway. Initially, genes hemA and hemL were overexpressed with strong promoters and synthetic 5'-untranslated regions (5'-UTRs). Then, the tricarboxylic acid (TCA) cycle was blocked to force carbon flux toward the ALA production pathway by deletion of sucA. Although the resulting strain showed a severe metabolic imbalance and low ALA production, further precise tuning of carbon flux to the glyoxylate cycle by varying the transcriptional strength of aceA led to substantially improved cell growth and ALA production. Thus, this precise tuning of the glyoxylate cycle in a quantitative manner should also enable efficient production of other value-added products derived from the TCA cycle.