CO2 fixation and lipid accumulation in biofilms of the aerial microalga Coccomyxa sp. KGU-D001 (Trebouxiophyceae)

This study compares lipid accumulation by immobilized aerial microalga Coccomyxa sp. KGU-D001 (Trebouxiophyceae) in biofilms and in aqueous suspended cultivation. Under direct exposure to normal air (low CO2) and light conditions, triacylglycerol (TAG) synthesis was significantly stimulated in algal biofilms on wet cotton wool. The TAG accumulation increased with decreasing thickness of the biofilm. This trend was attributed to CO2 fixation by photosynthesis of the biofilm cells, which increases the cellular accumulation of TAG. In a 17-μm-thick biofilm cultivated for 7 days, the total fatty acid (FA) content reached 27% of the cell dry weight. Under these conditions, approximately 60% of the fixed cellular carbon was presumed to be invested in TAG synthesis through free FAs. The CO2 fixation rate was almost maximized at relatively low photon flux density (25 μmol photons m−2 s−1). CO2-gas fixing algal biofilm systems can realize novel non-suspended cultivations, called artificial leaves, and thus present as strong candidates for biodiesel production in the near future.