Enhancing lead tolerance in spirulina using glycine betaine under high CO2 and salinity for sustainable carbon capture

Microalgae-based carbon capture and utilization (CCU) offers a promising negative emission technology that absorbs CO₂ and generates valuable biomass. However, heavy metal pollutants in industrial flue gases can compromise carbon sequestration efficiency and bioproduct quality. Spirulina was investigated as a model organism for CO₂ sequestration, using a modified Zarrouk’s medium to integrate salt stress and an osmoprotectant to boost biomass yield under 15 % CO₂. This approach enhances both biomass yield （380.83 mg L^–1 d^–1）and resistance to lead toxicity. Analytical assessments revealed that glycine betaine (GB) supplementation drastically reduced lead accumulation, decreasing the extracellular and intracellular contents by 39.7 % and 60.7 %, respectively. A notable decrease in extracellular dissolved organic matter was also observed. Furthermore, transcriptomic analyses confirmed that GB treatment strengthened osmotic stress responses and suppressed metal ion transport. These findings enhanced the feasibility of microalgae-based CCU technologies, marking significant progress in sustainable algal biotechnology.