Gas production reveals the metabolism of immobilized Chlorella vulgaris during different trophic modes

Abstract The metabolism of heterotrophic and mixotrophic cultivation modes of Chlorella vulgaris, a potential source of biofuel and CO2 mitigation, was studied in immobilized cultures. The gas concentration (O2 and CO2) was measured thanks to an original device manufactured using 3D printing. The biomass was monitored by 3D imaging and image processing. Net O2 and CO2 sources were obtained by a balance equation considering a calibrated leakage and the dissolved gas. Combined experimental and theoretical gas yields (mass of gas per mass of biomass), the photosynthesis proportion of mixotrophic colony was determined. Its increase with light intensity is not linear. Therefore, the highest light intensity ( 104 μ m o l ∙ m - 2 ∙ s - 1 ) revealed the limit of photosynthesis potential in the growth of mixotrophic colony. In the presence of light, the colony adopts a cylindrical shape instead of a spherical cap. This study proposed mechanisms of synergy inside the colony for heterotrophic and mixotrophic modes.