Time of culture harvest affects lipid productivity of nitrogen-starved Isochrysis galbana U4 (Isochrysidales, Haptophyta)

•The effect of nitrogen (N) on I. galbana lipid productivity was determined.•N-limitation resulted in fluctuations in lipid productivity.•Maximal lipid productivity was evident during the early stationary phase.•Lipid yield greatly influenced lipid productivity of this species.

The effect of nitrogen concentration on lipid accumulation, biomass productivity and lipid productivity in Isochrysis galbana U4 (Isochrysidales, Haptophyta) was tested. Nitrogen limitation induces fluctuations in the lipid productivity in this species. The lipid productivities were influenced to a greater extent by the lipid yield rather than by biomass productivity. Lipid productivities were maximal during the early stationary phase when lipid accumulation was initiated and declined as the stationary phase progressed which was attributed to the cessation in lipid accumulation when the upper limit to the lipid storage capacity of I. galbana cells was reached. Hence, the cost of I. galbana mass culture for lipid production, as biofeed for biodiesel, can be reduced by harvesting the cells during the early stationary phase, when lipid productivity is at a maximum. This would maximize lipid yields and reduce the duration of photo-bioreactor runs resulting in reductions in energy costs.