To improve the lipid accumulation of diatom cells, Nitzschia sp. was mutated by Co-60-gamma-ray irradiation and cultivated with high salinity. The biomass and lipid yields of Nitzschia sp. mutated by Co-60-gamma-ray irradiation at 900 Gy were increased by 53.8% and 28.1%, respectively. The lipid content of Nitzschia sp. mutant cells cultivated with gradually increased salinity of up to 30% was increased from 11.9% to 27.2%. This was because that the increased demand for nitrogen to keep cells healthy growth under high salinity conditions resulted in lipid accumulation, which was beneficial to prevent cell membranes from being destroyed by changing osmotic pressure. When the Nitzschia-ZJU1 strain obtained from Nitzschia sp. by irradiation mutation and salinity domestication was cultured in the growth media with no nitrogen and no silicon, the lipid content of cells was dramatically increased to 51.2%. (C) 2014 Elsevier Ltd. All rights reserved.