Bioconversion of CO₂ into valuable bioproducts via synthetic modular co-culture of engineered Chlamydomonas reinhardtii and Escherichia coli

With increasing concern over environmental problems and energy crises, interest in the biological conversion of CO₂ into bioproducts is growing. Although microalgae efficiently utilize CO₂, their metabolic engineering remains challenging. In contrast, while synthetic biology tools are advanced for many heterotrophic bacteria, these organisms cannot directly utilize CO₂. As such, a modular co-culture system with a glycolate dehydrogenase 1 (GYD1) deficient Chlamydomonas reinhardtii mutant and Escherichia coli was developed. The GYD1 mutant secretes glycolic acid via photorespiration, which E. coli metabolizes via the glyoxylate cycle. E. coli growth was improved by implementing two-stage continuous systems to 2.0 mg L⁻¹ h⁻¹ on CO₂. The production of green fluorescent protein (0.52 ng L⁻¹ h⁻¹) and lycopene (6.3 μg L⁻¹ h⁻¹) was also demonstrated. This study represents a successful case of a synthetic modular co-culture with a microalga and a heterotrophic bacterium, potentially contributing to sustainable industrial processes and reducing environmental impact.