Electrogenic Activity, Pigment Synthesis, and Protein Production in Limnospira indica at High Altitudes

Cyanobacteria are promising candidates for regenerative life-support systems in space exploration, where they could simultaneously recycle CO₂, supply O₂, and provide edible biomass. Here, we investigate the electrogenic activity and stress responses of Limnospira indica PCC 8005 under high-altitude conditions that mimic aspects of extraterrestrial environments. Using biophotoelectrochemical cells and liquid cultures deployed at the Jungfraujoch High Altitude Research Station (3572 m, Swiss Alps), we exposed cyanobacteria to reduced atmospheric CO₂, low temperatures, elevated UVA, high visible irradiance, and ionizing radiation, and ∼12-fold higher cosmic ray fluxes compared with ground level. Chronoamperometry revealed that global solar radiation accounted for over 80% of the variance in photocurrent, whereas temperature played only a minor role. Spectroscopic analysis showed significant decreases in chlorophyll and carotenoid content under high-altitude exposure, concurrent with a four- to fivefold increase in phycocyanin, consistent with chromatic adaptation and enhanced antioxidant defense. Protein analysis further revealed a redistribution toward higher-molecular-weight fractions, which suggests stress-induced remodeling of the cyanobacterial proteome. These results demonstrate that L. indica maintains electrogenic activity while undergoing adaptive pigment and protein adjustments under simultaneous high-altitude stressors. Our findings inform the design of biohybrid photoelectrochemical systems and highlight cyanobacteria as robust multifunctional agents for oxygen and fuel production in space life-support infrastructures.