Photoelectrocatalytic-Microbial Biohybrid for Nitrogen Reduction

Area of Science:

• Biotechnology and Bioengineering
• Materials Science
• Electrochemistry

Background:

• Nitrogen (N₂) to ammonia (NH₃) conversion under mild conditions remains a significant chemical challenge.
• Biological ammonia synthesis using whole-cell diazotrophs presents a promising sustainable strategy.
• Developing efficient biohybrid systems is crucial for artificial nitrogen fixation.

Purpose of the Study:

• To develop the first photoelectrochemical-microbial (PEC-MB) biohybrid for artificial nitrogen fixation.
• To interface Azotobacter vinelandii (A. vinelandii) with polydopamine encapsulated nickel oxide (NiO) nanosheets (NiO@PDA).
• To investigate the NH₃ production yield and mechanism in the developed biohybrid system.

Main Methods:

• Fabrication of NiO@PDA nanosheets for interfacing with A. vinelandii.
• Construction of the NiO@PDA/A. vinelandii biohybrid for nitrogen fixation.
• Operation of the biohybrid in both photoelectrochemical (PEC) and electrocatalytic (EC) modes.
• Analysis of ammonia production yield and underlying enhancement mechanisms.

Main Results:

• A novel NiO@PDA/A. vinelandii biohybrid was successfully constructed, demonstrating excellent A. vinelandii adsorption.
• The biohybrid achieved a record-high NH₃ production yield of 1.85 µmol h^-1/10⁸ cells (4.14 µmol h^-1 cm^-2).
• The system operated effectively under both illumination (PEC) and dark (EC) conditions for sustained NH₃ synthesis.
• Enhanced NH₃ synthesis was attributed to increased NADH and ATP levels and overexpression of key nitrogenase genes (nifH, nifD, nifK).

Conclusions:

• The developed PEC-MB biohybrid represents a significant advancement in artificial nitrogen fixation.
• This biohybrid system offers a sustainable and efficient method for ammonia production.
• The study provides fundamental insights into the mechanisms of bio-abiotic photosynthetic systems for chemical synthesis.