Redox regulation of hydrogen production in Escherichia coli during growth on by-products of the wine industry

Area of Science:

• Biotechnology
• Microbial Hydrogen Production
• Bioelectrochemical Systems

Background:

• Lignocellulosic wine grape waste (WGW) is an abundant, low-cost substrate for microbial fermentation.
• Escherichia coli can efficiently convert WGW into valuable products like hydrogen gas (H2).
• Controlling the initial redox potential (oxidation-reduction potential, ORP) of the fermentation medium can significantly influence microbial growth and product yields.

Purpose of the Study:

• To investigate the impact of initial ORP on the growth, H2 production, and current generation of E. coli using WGW hydrolysate.
• To evaluate the performance of both wild-type and a H2-optimized mutant strain of E. coli under varying ORP conditions.
• To assess the potential of E. coli cells grown under optimized ORP as anode catalysts in bio-electrochemical fuel cells.

Main Methods:

• Cultivation of E. coli (parental and mutant strains) anaerobically on pre-treated WGW hydrolysate at different dilutions and pH.
• Adjustment of initial ORP using redox reagents like DL-dithiothreitol (DTT).
• Measurement of biomass formation (OD600), H2 production (mmol/L), ORP kinetics, and electrical potential (V) in bio-electrochemical systems.

Main Results:

• A twofold diluted WGW medium with pH adjustment (K2HPO4) reduced acidification, prolonged H2 production, and enhanced biomass (OD600, 1.5).
• Addition of DTT positively influenced H2 production in both strains, with H2 production starting earlier under reduced ORP conditions.
• The septuple mutant strain grown under reduced ORP conditions yielded the highest electrical potential (up to 0.7 V) when used as anode catalyst.

Conclusions:

• Modifying medium buffering capacity and ORP are effective strategies to improve biomass yield and H2 production from WGW.
• Reduced ORP conditions enhance H2 yield and facilitate microbial current generation in bio-electrochemical systems.
• Optimized E. coli strains grown under controlled ORP show promise for biotechnological biocatalyst applications.