BackgroundLarge improvements in productivity are required to make massive scale biodiesel production from microalgae an economic reality. Although the maximum neutral lipid content of microalgae has received much attention as a target for optimization, there are other factors that are equally important. These are (1) the rates of accumulation of both biomass and lipids and (2) the maximum densities of algal cells that can be sustained in continuous cultivation. The combined effect of these factors for lipid production has not been thoroughly examined in Dunaliella species. Hence this study examines the rates of growth and lipid accumulation in Dunaliella salina using Fourier transform infrared spectroscopy (FTIR) under several combinations of temperatures and cell densities. ResultsThe FTIR signal at 2926cm(-1) (rather than 1740cm(-1)) is better for measuring lipids and the PCA of the full spectrum showed a clear separation between the nitrogen replete and nitrogen depleted cells. As expected, cells subjected to nitrogen starvation (N-depleted) showed very little growth compared to the N-replete cells. N-depleted cells achieved a final lipid content that was 78% more than the N-replete samples at 26 degrees C, while the differential for 16 degrees C was 28%. However, the slower growth rates caused by the stress of nitrogen starvation meant that the total lipid production over the starvation period was lower for many samples. Indeed, the only stress condition that gave significantly higher total lipid production was the highest cell density studied at 26 degrees C. ConclusionFor optimization of lipid productivity for biodiesel, the trade-off between lipid content, growth rate and cell density needs to be considered. (c) 2013 Society of Chemical Industry