Constraint-based mathematical model analysis reveals glycogen and cellulose storage competition during conversion of CO2 to hyaluronic acid in Chlorella vulgaris

Hyaluronic acid (HA) is a biopolymer with a wide range of biomedical and industrial applications. Conventionally, it is manufactured from rooster comb and fermentation of Streptococcus zooepidemicus. In this work, we explore hyaluronic acid production under phototrophic conditions using a reduced-scale, constraint-based in silico microalgal model comprising 216 reactions, 144 metabolites, and 318 genes, reconstructing a microalgal system. In model validation, verify stoichiometric consistency, phototrophic conditions, and constraints, and also check for leaks in reaction flux. Single limiter analysis shows the HA production steadily increases with photon from (0.05 to – 0.31 mmol gDW⁻¹ h⁻¹), and CO₂ (0.1 to 1 mmol gDW⁻¹ h⁻¹), uptake, indicating strictly resource-limited biosynthesis. Trade-off analysis between biomass-HA under phototrophic growth, where the wild-type state produced HA = 0.26 mmol gDW⁻¹ h⁻¹ with biomass flux ~ 3.88–4.00 mmol gDW⁻¹ h⁻¹. Enforcing storage allocation activated glycogen and cellulose sinks, diverting carbon away from HA and decreasing HA to ~ 0.15 mmol gDW⁻¹ h⁻¹, along with reduced growth. Pareto and weighted-sum optimization revealed a steep, non-smooth front, indicating discrete switching between growth and HA-dominated metabolic states. Knockout of the competing storage reactions redirected carbon toward HA biosynthesis, recovering HA to ~ 0.26 mmol gDW⁻¹ h⁻¹ without decreasing biomass growth.