Breeding 3 elite strains of Nannochloropsis oceanica by nitrosoguanidine mutagenesis and robust screening

Abstract

Nannochloropsis have received extensive attention for biodiesel production in recent years. By integrating random mutation with a robust and cost-efficient screening method, we bred three mutants (LAMB001, LAMB002 and LAMB003) of Nannochloropsis oceanica featuring higher lipid productivity than wild-type N. oceanica. This screening included BODIPY 505/51511BODIPY 505/515: (4,4-difluro-1, 3, 5, 7-tetramethyl-4-bora- 3a,4adiaza-s-indacene). staining and fluorescence microplate reading, during which the optimal concentration (0.225μg/mL) of BODIPY 505/515 was determined for the staining of N. oceanica. Nitrosoguanine was proven to be more potent than ethyl methane sulfonate in mutating lipid-rich strains. The three mutants exhibited increases of 33.54%, 30.93% and 21.44% in lipid productivity over that of wild-type-type Nannochloropsis oceanica. Compared to wild-type N. oceanica, the lipid content of LAMB001, LAMB002 and LAMB003 increased by 17.4%, 23.7% and 29.4%, respectively, with LAMB003 accumulating the most lipid, accounting for 31.34% of dry biomass. The fatty acid profile indicated that C16–C18 of LAMB003 increased by 12.56% relative to that of the wild-type, totaling 66.59% of total fatty acids. Comparisons of the triacylglycerol composition between wild-type N. oceanica and LAMB003 indicated that TAG (18:0/18:1/20:5) and TAG (16:0/16:0/20:5) were absent in LAMB003, which was in accordance with its depressed PUFA22PUFA: polyunsaturated fatty acid. content (29.46%)