Strain engineering for high-level 5-aminolevulinic acid production in
Escherichia coli
Abstract
As issues surrounding depleting fossil fuels, climate change, and
various other environmental impacts are becoming more prevalent, there
is a growing interest in technological shifts toward a bio-based
economy. Various advanced biotechnological tools have been developed to
customize cell factories for the production of a wide range of complex
fine chemicals from renewable feedstock. Herein, we report development
of a microbial bioprocess for high-level and potentially economical
production of 5-aminolevulinic acid (5-ALA), a valuable
non-proteinogenic amino acid with multiple applications in medical,
agricultural, and food industries, using Escherichia coli as a cell
factory. We first implemented the Shemin (i.e., C4) pathway for
heterologous 5-ALA biosynthesis in E. coli. To reduce, but not to
abolish, the carbon flux toward essential tetrapyrrole/porphyrin
biosynthesis, we applied Clustered Regularly Interspersed Short
Palindromic Repeats interference (CRISPRi) to repress hemB expression,
leading to extracellular 5-ALA accumulation. We then applied metabolic
engineering strategies to direct more dissimilated carbon flux toward
the key precursor of succinyl-CoA for enhanced 5-ALA biosynthesis. Using
these engineered E. coli strains for bioreactor cultivation, we
successfully demonstrated high-level 5-ALA biosynthesis solely from
glycerol (~30 g l-1) under both microaerobic and aerobic
conditions, achieving up to 5.95 g l-1 (36.9% yield) and 6.93 g l-1
(50.9% yield) 5-ALA, respectively. This study represents one of the
most effective bio-based production of 5-ALA from a structurally
unrelated carbon to date, highlighting the importance of integrated
strain engineering and bioprocessing strategies to enhance bio-based
production.