Enhancing biomass productivity in Chlorella sorokiniana via electrostimulation and its optimization by algal-bacterial co-culture

Abstract

Microalgae have emerged as one of the most promising biological platforms for biomass production. However, their biomass productivity is largely constrained by insufficient energy supply. This study investigates electrostimulation-driven exogenous electron uptake (EEU) coupled with the modulation of EPS-mediated interfacial electron transfer to enhance microalgal biomass productivity. By using interdisciplinary methods including contact-blocking experiments, bioelectrochemistry, liquid chromatography-mass spectrometry, and chlorophyll fluorescence, it has been revealed that Chlorella sorokiniana (C. sorokiniana) can perform direct EEU, and electrons derived from EEU can flow into the photosynthetic electron transport chain and drive adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH) syntheses. Moreover, by monitoring changes in cellular metabolism and structure under electrostimulation, it was found that besides supplying extracellular electrons, electrostimulation can induce cellular oxidative stress, significantly increasing intracellular reactive oxygen species (ROS) levels, lipid contents, and the activities of superoxide dismutase (SOD) and catalase (CAT), while stimulating extracellular polymeric substances (EPS) synthesis and thickening the EPS layer, which increases the distance between the cell center and the cathode surface, thereby reducing electron transport efficiency. To dynamically regulate microalgal EPS thickness, a co-culture optimization strategy was explored by introducing Shewanella putrefaciens, a bacterium capable of utilizing algal EPS as nutrients, to mitigate excessive EPS accumulation, thereby relieving the interfacial electron transport barrier and further enhancing cell growth and biomass productivity of C. sorokiniana. This study provides a feasible strategy to alleviate the energy limitation on microalgal growth and biomass productivity.