At high temperature lipid production in Ettlia oleoabundans occurs before nitrate depletion

Temperature and light intensity effects on biomass and lipid production were investigated in Ettlia oleoabundans to better understand some fundamental properties of this potentially useful but poorly studied microalgal species. E. oleoabundans entered dormant state at 5 A degrees C, showed growth at 10 A degrees C, and when exposed to light at 70 mu mol photons per square meter per second at 10 A degrees C, cells reached a biomass concentration of > 2.0 g L-1 with fatty acid methyl esters of 11.5 mg L-1. Highest biomass productivity was at 15 A degrees C and 25 A degrees C regardless of light intensity, and accumulation of intracellular lipids was stimulated by nitrate depletion under these conditions. Although growth was inhibited at 35 A degrees C, at 130 mu mol photons per square meter per second lipid content reached 10.37 mg L-1 with fatty acid content more favorable to biodiesel dominating; this occurred without nitrate depletion. In a two-phase temperature shift experiment at two nitrate levels, cells were shifted after 21 days at 15 A degrees C to 35 A degrees C for 8 days. Although after the shift growth continued, lipid productivity per cell was less than that in the 35 A degrees C cultures, again without nitrate depletion. This study showed that E. oleoabundans grows well at low temperature and light intensity, and high temperature can be a useful trigger for lipid accumulation independent of nitrate depletion. This will prove useful for improving our knowledge about lipid production in this and other oleaginous algae for modifying yield and quality of algal lipids being considered for biodiesel production.