Light-induced coupling of bioelectricity generation and nitrogen assimilation in algal cathode microbial fuel cells

Algal cathode microbial fuel cells (MFCs) are a promising technology for simultaneous wastewater treatment and bioenergy recovery. However, the fundamental mechanisms of light-mediated 'light-electricity-nitrogen' coupling via photosynthetic metabolites remain unclear, hindering system optimization. This study introduces a novel, simplified model using a defined co-culture of electrogenic Shewanella putrefaciens CN32 and Nannochloropsis oceanica in a dual-chamber MFC to decipher these interactions. Results show that light intensity critically regulates system performance, with an optimal range of 2000-5000 Lux. Within 48 h, this system achieved 49 % total nitrogen removal, a peak current density of 21.05 mA/m², and a minimal charge transfer resistance (4.424 Ω). Mechanistically, photosynthetic oxygen plays a dual role: By enhancing algal nitrogen assimilation and central carbon metabolism, it facilitates the cathodic oxygen reduction through the synergy of biofilm porosity and extracellular polymeric substance-mediated electron shuttling. Furthermore, transcriptomic analysis revealed the molecular basis of this synergy, showing that light exposure upregulates algal genes for nitrogen transport and photosynthetic apparatus maintenance. This work elucidates the light-electricity-nitrogen network, demonstrating how light-regulated metabolites optimize pollutant removal and energy recovery, thereby establishing a theoretical foundation for sustainable algal bioelectrochemical applications.