Improved Photosynthetic Efficiency And Lipid Productivity Of Nannochloropsis By Heavy-ion Irradiation Mutagenesis

In this study, heavy-ion irradiation mutagenesis was applied in Nannochloropsis oceanicaOZ-1breeding, a promising species in microalgal biodiesel commercialization. After large-scalescreening, two mutants (HP-1and HP-2) with higher photosynthetic efficiency were isolatedfrom the wild type N. oceanica. Subsequently, their biomass and lipid accumulation as well asphotosynthetic efficiency during cultivation were investigated. The results showed biomassaccumulation of the two mutants at the end of18-day cultivation were increased by19%and26%compared to the wild type, respectively. The reason may due to their higher photosyntheticefficiency from the higher pigment content and the higher photosynthetic oxygen evolution rateresults of both mutants. To investigate their lipid accumulation, a second-stage cultivation modelwas applied. The results showed lipid content of the mutants were not significantly increased, butdue to their higher biomass accumulation, their lipid productivity were increased by19%(295mg L-1d-1) and11%(275mg L-1d-1) compared to the wild type (247mg L-1d-1). The reasonmay result from its higher photosynthetic efficiency than that of the wild type during lipidaccumulation. Further, lipid composition analysis indicated TAG content of HP-1was14%higher, while polar lipid content was15%lower than that of wild type, then fatty acid profileanalysis revealed that the content of saturated fatty acids in HP-2was significantly increased by20%, while the content of unsaturated fatty acids decreased by25%compared to those in wildtype. In conclusion, both mutants (HP-1and HP-2) could be considered as ideal candidate infuture microalgae commercialization due to their higher biomass accumulation and lipidproductivity.