An axenic strain reveals the responses of Phaeodactylum tricornutum to external organic carbon

The model diatom Phaeodactylum tricornutum is considered a promising source of various high value bioproducts, and developing cultivation processes is crucial for its commercialization. Although mixotrophy and heterotrophy have been recommended as effective strategies for microalgal cultivation, previous studies on P. tricornutum have yielded conflicting results in terms of cultivating this microalga. To verify the capacity of this microalga utilizing external organic carbon, both heterotrophic and mixotrophic cultivation with varied carbon sources were performed using an axenic strain. The results demonstrate that glycerol was the only organic carbon that substantially stimulated the growth of P. tricornutum in the presence of light. Sodium acetate (NaAc) at low concentrations could also promote growth, while at high concentrations led to severe inhibition under mixotrophic conditions. The addition of glucose imposed no appreciable impact on either cell density or biomass concentration, confirming that P. tricornutum cannot metabolize external glucose. Subsequently, a comparative analysis between mixotrophy and autotrophy was performed to reveal the influences of glycerol on the cellular metabolism based on growth performances, biochemical compositions, and chlorophyll fluorescence parameters. Results also indicate that the addition of glycerol did not have detrimental effects on the capacity of either pigments biosynthesis or photosynthesis, but enhanced the saturated fatty acids and reduced the unsaturated fatty acids.