Isolation of thermo-tolerant and high lipid content green microalgae: Oil accumulation is predominantly controlled by photosystem efficiency during stress treatments in Desmodesmus

► New thermo-tolerant and high lipid content microalgae were isolated from a subtropical location. ► Three microalgae accumulated more than 50% of lipids in dry mass under nitrogen starvation. ► Triglycerides constituted around 75% of the total lipids in the three microalgae. ► Oil yields under stress treatments positively correlated with their photosystem efficiencies. Discoveries of new microalgae with thermo-tolerance, high growth rate, and high lipid content are crucial to algal biodiesel production in tropical and subtropical zones. Four new green microalgae were isolated in southern Taiwan. All four species are members of the genus Desmodesmus under the family Scenedesmaceae based on molecular and morphological analyses. Two of the four species survived at 45°C for 24h, with 5–13% of mortality rates caused by the heat. Total lipid contents of the two species reached over 50% in dry biomass under nitrogen starvation, and their triacylglycerols constituted around 75% of the total lipids. Thus the two species are good potential feedstocks for biodiesel production. Oil accumulation in the four species positively correlates with their photosystem II efficiencies during stress treatments (R2=0.90). This finding further supports that photosynthesis is essential for oil body formation under nitrogen starvation in green microalgae.