Synergistic conversion of CH₄ and CO₂ into bioplastic by microalgal−bacterial consortia

Conversion of methane (CH₄) and carbon dioxide (CO₂) into value-added products is a promising strategy for simultaneously reducing greenhouse gas emissions and enhancing the utilization of renewable carbon resources. However, high dissociation energies of the C–H bond in CH₄ and the C=O bond in CO₂ typically necessitate energy-intensive physicochemical conversion processes. Herein, the co-culture system of Chlorella pyrenoidosa and Methylocystis hirsuta was constructed to simultaneously convert CH₄ and CO₂ to polyhydroxybutyrate (PHB) at mild condition. Compared with the monoculture, the co-culture system significantly enhanced biomass accumulation (1181.48 vs 777.78 mg/L), methane utilization rate (1.22 vs 0 mmol/d), and PHB yield (43.97 vs 6.72 mg/L) through respiratory interaction and nutrient exchange. Furthermore, optimal PHB synthesis of co-culture system was obtained with a gas composition of 70 % CH₄ and 30 % CO₂. Transcriptomic analysis showed that the upregulation expression of genes related to methane metabolism (pmoABC) and butanoate metabolism (phaC) in the microalgal−bacterial consortia system improved CH₄ oxidation and PHB synthesis of M. hirsuta. Additionally, co-culture facilitated the nitrogen consumption coupled with the significantly downregulation of sulfur metabolism-related genes, creating a nutrient-limited environment that further promoted PHB accumulation. This study provides a green and sustainable approach for conversion greenhouse gases into high-value products through methanotrophic-based biomanufacturing, and offers an innovative engineering technology for the upcycling of greenhouse gases.