Mass Balance of the Major Cellular Carbon Pools for the Marine Diatom Thalassiosira pseudonana as Regulated by Irradiance, CO2, and Growth Phase

Salt tolerant strains of photosynthetic microalgae are promising as a potential new commodity-scale source of biomass for renewable fuels, biomaterials, animal feeds, and human nutraceuticals. Understanding the dynamics of carbon allocation among the cellular pools as a function of the algae cultivation environment is essential for predicting production yields of the biomass components of economic interest. We investigated the effect of irradiance and CO2 on the cellular accumulation of fatty acids, pigments, carbohydrates, and proteins in the marine diatom Thalassiosira pseudonana. Triplicate batch cultures were grown at 18 °C using saturating and non-saturating irradiance levels in combination with ambient and elevated CO2 concentrations. Carbon allocation was quantified during mid-log (balanced) growth, and stationary phase when metabolism is unbalanced and allocation between carbon pools shifts. Dynamic changes were observed in total carbon partitioning as well as fatty acid and pigment profiles. The percentage of cellular carbon allocated to lipid storage reached a maximum of 45.19 ± 8.20% during stress-induced stationary phase but were significantly lower during mid-log phase. Pigments accounted for a maximum of 4.30 ± 0.46% of cellular carbon during mid-log growth and were significantly lower during stationary phase. Significant trends in fatty acid and pigment profiles based on differences in environmental parameters and growth phase were also observed. We accounted for an average of 85% of cellular carbon based on quantifying the carbon quota in the lipid, protein, carbohydrate, and pigment pools. In this study, we quantify the changes in carbon allocation of the bulk metabolome for Thalassiosira pseudonana at sub-saturating and saturating irradiance during balanced exponential growth with adequate nutrients and during unbalanced metabolism with the onset of stationary phase induced by nutrient depletion.