Sethoxydim-resistant mutants of the thermotolerant microalga Micractinium sp. accumulate significant amounts of triacylglycerol in non-stressful conditions

Because of their high lipid content, microalgae are regarded as a potentially competitive source for biofuels. However, one of the main biotechnological challenges in algae-based biofuels is that cell division is arrested under conditions which promote lipid accumulation, resulting in reduced overall lipid yield. In this study, sethoxydim-resistant mutants of the promising thermotolerant green microalga Micractinium sp., which has a relatively fast growth rate and tolerance to outdoor high temperatures, were generated by UV-C mutagenesis for increased cellular triacylglycerol (TAG) without compromising on growth rate. Two Micractinium mutants were isolated (designated as Mut 3 and Mut 4) that displayed significant increase in TAG cell content up to 71% and 84%, with decreased chlorophyll content by 37% and 38%, respectively, compared with the wild-type cells. Final TAG culture productivity of Mut 3 and Mut 4 were also greater, reaching up to 0.61 ± 0.01 and 0.62 ± 0.02 g L⁻¹, respectively, compared with the wild-type culture of 0.40 ± 0.03 g L⁻¹. The mutants were stable without using antibiotics or any other chemicals during the experiments and preservation. These results highly nominate the mutants of Micractinium sp. isolated in this work as potential microalgae candidates to serve as a feedstock for sustainable and cost-effective biofuel production.