Carbon-Mediated Rechargeable Operation for Light-Driven Ammonia Production Using Quantum Dot- Azotobacter vinelandii Hybrids

Information from the abstract

Integrating diazotrophic microorganisms with semiconductor nanomaterials enables nitrogen (N 2 )-to-ammonia (NH 3 ) conversion under ambient conditions, yet most studies are evaluated using washed cells in carbon-free buffers, obscuring metabolic controls for scalable operation. Here we report that medium carbon status governs light-driven extracellular NH 4 + accumulation and long-term production in a quantum dot (QD)- Azotobacter vinelandii hybrid. The hybrid exhibits increased membrane polarization under illumination, accompanied by elevated intracellular NADH/NAD + and ATP, and NH 4 + production is strongly inhibited by a protonophore that dissipates the membrane electrochemical gradient and blocks ATP synthesis, indicating ATP-dependent nitrogenase catalysis. In sucrose-rich medium, extracellular NH 4 + accumulation remains low as fixed nitrogen is preferentially assimilated into biomass, while excess carbon is stored as polyhydroxybutyrate (PHB). Upon sucrose depletion, PHB is mobilized and extracellular NH 4 + accumulation becomes apparent. Using this carbon switch, intermittent sucrose feeding (1 g L –1 ) during 12 h dark intervals enabled rechargeable cycling and increased cumulative NH 4 + production by ∼2.4-fold over 108 h. These results link QD photoredox input to mediator-assisted electron transfer, cellular bioenergetics, and carbon reserve metabolism and fixed-nitrogen allocation, providing design principles for semiconductor-diazotroph platforms.

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Related topics: Ammonia Synthesis and Nitrogen Reduction · Microbial Fuel Cells and Bioremediation · Anaerobic Digestion and Biogas Production