In order to produce biodiesel from microalgae cultured with abundant seawater, Chlorella sp. was mutated with Se-137-gamma ray irradiation and domesticated with f/2 seawater culture medium (salinity = 3 wt.%) under 15 vol.% CO2 stress. Biomass yield of the mutant increased by 25% compared with wild species and lipid content increased to 54.9%. When nitrogen and phosphorus concentrations in the initial substrate increased, the increased propagation speed of the mutant resulted in decreased cell diameter by 26.6% and decreased cell wall thickness by 69.7%. The dramatically increased biomass yield of the mutant with sufficient initial substrate and relative nitrogen starvation in the later growth period with continuous 15 vol.% CO2 led to an increased lipid yield of 1.0 g/L. The long-chain unsaturated fatty acids increased, whereas short-chain saturated fatty acids decreased. (C) 2015 Elsevier Ltd. All rights reserved.