A microbial electrochemical system enables the energy-efficient conversion of cyanobacterial biomass into plant fertilizer for Mars

• Microbial anode converts cyanobacterial biomass into plant-available nutrients • Co-inoculation with Geobacter sulfurreducens required for current generation • Microbial electrochemical system operated with Martian regolith simulant leachate • Anodic and planktonic microbial communities were characterized Producing significant amounts of food on Mars will be challenging, as crops could not grow solely on local resources. One promising solution lies in first cultivating cyanobacteria using Martian regolith, sunlight, water, and atmospheric gases (N₂, CO₂), and in then using the cyanobacterial biomass as plant feedstock. However, this biomass must first be mineralized—removing organic carbon, releasing ammonium, and solubilizing nutrients—to be utilized efficiently by plants. Microbial electrochemical systems can enable this conversion while providing a broad range of products and services. This study explores how a microbial anode can transform cyanobacterial biomass into more plant-accessible nutrients and recover its chemical energy content as hydrogen. Three fermentative inocula were tested in minimal media by themselves and in combination with Geobacter sulfurreducens , a known exoelectrogen. Current was produced exclusively when G. sulfurreducens was co-inoculated, resulting in an average chemical oxygen demand (COD) removal of 38 %, a coulombic efficiency of 68 %, and a maximum current density of 3.7 mA per g of stainless-steel wool anode. The system was then successfully operated using leachate from a Martian regolith simulant as the primary mineral nutrient source, yielding 37 % COD removal, 49 % coulombic efficiency, and 3.5 mA g⁻¹ maximum current density. The bacterial and archaeal communities of the planktonic phase and anode were characterized to further understand the microbial composition of bioelectrochemical systems. The cell’s anolyte appeared suitable for hydroponic cultivation, highlighting the potential of bioelectrochemical systems to support food production and resource recycling in a Martian settlement.