Combined exploitation of CO2 and nutrient replenishment for increasing biomass and lipid productivity of the marine diatoms Thalassiosira weissflogii and Cyclotella cryptica

Diatoms are promising candidates for sustainable production of biofuels but their use is restricted due to the difficulties of combining high-biomass productivity and lipid accumulation. Here, we report the effect of high levels of nutrients and supplementation of 10% CO2 on biomass and lipid productivity of the marine diatoms Thalassiosira weissflogii and Cyclotella cryptica. Daily nutrient replenishment stimulated growth and increased the biomass but reduced lipid synthesis and dropped the level of triglycerides (TAG) close to zero. On the contrary, addition of 10% CO2 (v/v) doubled or tripled lipid content in comparison with air-sparged cultures, but induced only a modest increase of biomass. Assessment of the content in carbohydrates, lipids, and proteins suggested that CO2 stimulated lipogenesis from carbohydrates in both diatoms. In order to combine these effects, we also tested a two-stage cultivation that alternated nutrient replenishment together with addition of CO2 during nutrient shortage. T. weissflogii and C. cryptica responded to these conditions by increasing dry biomass to 1.25 g L-1 without reduction of total lipid percentage. In both species, TAG became the main lipid component and accounted for more than 60% of total glycerolipids in C. cryptica. These results underline the metabolic plasticity of diatom cells and indicate a possible way to maximize the production of biomass and functional products by tuning culture conditions.