Screening the diatom Nitzschia sp. re-mutated by ¹³⁷Cs-γ irradiation and optimizing growth conditions to increase lipid productivity

Abstract

Nitzschia ZJU1, which originated from the diatom Nitzschia sp. (ash free dry weight of biomass was 0.12 g L⁻¹ and its lipid content was 13.34 %) after ⁶⁰Co-γ ray irradiation and domestication at high-salinity, was re-mutated by ¹³⁷Cs-γ irradiation to increase lipid productivity. The lipid yields of the new mutants Nitzschia ZJU2 and Nitzschia ZJU3, which were selected by Nile Red fluorescence, were increased from 209.9 mg L⁻¹ (for the original Nitzschia ZJU1) to 245.5 mg L⁻¹ and 311.6 mg L⁻¹, respectively. The lipid content of the two strains increased to 64.42 and 62.61 % of ash free dry weight, respectively, when the cells were cultured with nitrogen and silicon deprivation. It was found that 3,063 reads of genetic expression including Acetyl-CoA carboxylase and other important genes in lipid synthesis pathway were up-regulated and 4,598 reads of genetic expression were down-regulated in mutant Nitzschia ZJU2, when the cells were cultured in optimized growth medium without nitrogen and silicon. The gene expression levels of ATP-binding cassette transporters, arginine and proline metabolism, and proteasome in metabolic pathways were up-regulated to different degrees in mutant Nitzschia ZJU2 under the same cultivation condition.