Boosting algal lipids: Diurnal shifts in temperature exceed the effects of nitrogen limitation

Algal lipids have been observed to increase during autumn conditions (low light, low mean temperature, and diurnal shift in temperature), in large-scale outdoor photobioreactors. In this paper, we tested the effect of diurnal shifts in temperature (DS) and nitrogen (N) limitation on algal BODIPY lipid fluorescence cell(-1) (BPF). We show that DS increased BPF in algal biomass up to 28% more compared with N limitation, the standard stressor to boost neutral lipids (NL) in commercial production. Biomass yield was constant, regardless the DS range (6 degrees C-12 degrees C). A combination of both stressors had an additive effect on algal BPF. A polyculture from an outdoor photobioreactor was cultivated under controlled conditions at different regimes of light, temperature, and N limitation. DSs were mimicking autumn conditions with a difference of 6 degrees C, 10 degrees C, and 12 degrees C between day and night. Biomass and BPF were monitored over one to two weeks, and NLs were stained with a fluorescent marker (BODIPY) and detected with flow cytometry. Results indicate that, during autumn conditions, daily heating and cooling processes in contrast to N limitation do not challenge the trade-off between biomass production and BPF. During seasons when day temperature is still relatively high, DSs are rapid BPF boosting stressors, while N limitation could be applied to boost BPF further during other seasons.