Metabolic modelling of the effects of CO2 on mixotrophic microalgal cultivation

Microalgae have great potential for bio-sequestration of CO2 into macromolecules such as lipids and carbohydrates for the production of biodiesel and bioethanol, respectively. The primary metabolic step involves the conversion... [ view full abstract ]

Microalgae have great potential for bio-sequestration of CO₂ into macromolecules such as lipids and carbohydrates for the production of biodiesel and bioethanol, respectively. The primary metabolic step involves the conversion of RuBP to GAP through the Calvin Cycle in the presence of RuBisCO enzyme. Alternatively, photorespiration adds O₂ to RuBP, producing 3-PGI. Both steps require O₂ and the synthesis of ATP, NADPH via coupled light reactions in the chloroplast. GAP converts to lipids via glycolysis and the TCA Cycle, and/or to carbohydrates through G6P via Gluconeogenesis. G6P also enters the Pentose Phosphate pathway yielding NADPH and Ru5P, which produce protein precursor nucleotides.

This metabolic modelling attempts to quantify the effects of CO₂, O₂ and nutrient supply at the reactor scale on the molecular scale reactions and the metabolic pathways for macromolecule synthesis that determines carbohydrate and lipid yields in mixotrophic cultivation of microalgae.

Our metabolic model is validated using experimental data on the concentrations of algal biomass, chlorophyll, lipids, carbohydrates, proteins, and dissolved CO₂ and O₂, available in the existing literature. This model attempts to integrate molecular pathways to reactor variables, and quantify their coupled effects on lipid and carbohydrate yields in mixotrophic algal cultivation.