Simultaneous growth and neutral lipid accumulation in microalgae

[Display omitted] ► Nitrogen limitation in turbidostats causes a metabolic energy imbalance in microalgae. ► This energy imbalance allows simultaneous cell replication and TAG accumulation. ► Neochloris oleoabundans used TAG as an energy sink when exposed to excess light energy. ► Excess light energy was predominantly dissipated rather than stored in TAG. In this paper the hypothesis was tested whether TAG accumulation serves as an energy sink when microalgae are exposed to an energy imbalance caused by nutrient limitation. In our continuous culture system, excess light absorption and growth-limiting nitrogen supply rates were combined, which resulted in accumulation of TAG (from 1.5% to 12.4% w/w) in visible lipid bodies in Neochloris oleoabundans, while cell replication was sustained. A fourfold increase in TAG productivity showed that TAG indeed served as an energy sink. However, the bulk of excess energy was dissipated leading to a significantly reduced biomass productivity and yield of biomass on light. This demonstrates that when aiming at industrial TAG production, sustaining efficient light energy use under nutrient stress is an important trait to look for in potential production organisms.