Enhancing growth rate and lipid yield of Chlorella with nuclear irradiation under high salt and CO2 stress

In order to produce biodiesel from microalgae cultured with abundant seawater, Chlorella sp. was mutated with 137Se-γ 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.