Persistent low PHB accumulation during pilot-scale gas fermentation in Cupriavidus necator

Area of Science:

• Biotechnology
• Sustainable Chemistry
• Microbiology

Background:

• Climate change and food security are critical global issues.
• Gas fermentation converts CO₂ to microbial single-cell protein (SCP) using hydrogen-oxidizing bacteria (HOB).
• Intracellular polyhydroxybutyrate (PHB) accumulation reduces SCP yield by diverting carbon and energy.

Purpose of the Study:

• To investigate methods for minimizing PHB accumulation during autotrophic gas fermentation.
• To optimize conditions for enhanced SCP production in Cupriavidus necator H16.
• To evaluate quantification methods for PHB and biomass.

Main Methods:

• Autotrophic gas fermentation of Cupriavidus necator H16 under optimized conditions.
• Analysis of PHB content using Gas Chromatography-Flame Ionization Detection (GC-FID) and High-Performance Liquid Chromatography with Ultraviolet detection (HPLC-UV).
• Time-course analysis of fermentation processes over 48 hours.

Main Results:

• Optimized fermentation conditions resulted in low PHB accumulation (~6% cell dry weight).
• HPLC-UV demonstrated superior speed, safety, and green chemistry compliance compared to GC-FID.
• Consistent and low PHB levels were observed under optimized, non-limiting conditions.

Conclusions:

• Tailored process control effectively suppresses PHB accumulation in wild-type Cupriavidus necator.
• Suppressed PHB enhances carbon conversion efficiency towards SCP production.
• This approach supports SCP as an energy-efficient, climate-resilient protein source for food and feed.