Corynebacterium glutamicum tailored for efficient isobutanol production

Area of Science:

• Metabolic Engineering
• Synthetic Biology
• Microbial Biotechnology

Background:

• *Corynebacterium glutamicum* is a versatile host for microbial production.
• Efficient production of biofuels like isobutanol requires significant metabolic engineering.
• Previous work established *C. glutamicum* for 2-ketoisovalerate production.

Purpose of the Study:

• To engineer *C. glutamicum* for efficient isobutanol production from glucose under oxygen deprivation.
• To identify key enzymes and metabolic pathways involved in isobutanol biosynthesis.
• To optimize isobutanol yield and productivity in a fed-batch fermentation process.

Main Methods:

• Genetic engineering of *C. glutamicum* by targeted gene inactivation and overexpression.
• Implementation of heterologous genes for isobutanol production pathway.
• Fed-batch fermentation under controlled aerobic and oxygen-depleted phases.
• Analysis of isobutanol yield (Y(P/S)) and volumetric productivity.

Main Results:

• Engineered strain achieved a substrate-specific yield of 0.77 ± 0.01 mol isobutanol per mol glucose via overexpression of *adhA*.
• Identified a native alcohol dehydrogenase as crucial for isobutanol formation.
• Demonstrated significant isobutanol production (175 mM) with a volumetric productivity of 4.4 mM h⁻¹ in fed-batch fermentation.
• Elucidated the role of the malic enzyme in cofactor regeneration (NADH to NADPH).

Conclusions:

• Metabolic engineering of *C. glutamicum* is effective for high-yield isobutanol production.
• Optimization of native and heterologous pathways is critical for enhancing biofuel synthesis.
• The engineered strain and fermentation strategy show promise for industrial-scale isobutanol manufacturing.