Abstract
Microalgae have received significant attention as potential next-generation microbiologic cell factories for biofuels. However, the production of microalgal biofuels is not yet sufficiently cost-effective for commercial applications. To screen higher lipid-producing strains, heavy carbon ion beams are applied to induce a genetic mutant. An RNA-seq technology is used to identify the pathways and genes of importance related to photosynthesis and biofuel production. The deep elucidation of photosynthesis and the fatty acid metabolism pathway involved in lipid yield is valuable information for further optimization studies. This study provided the photosynthetic efficiency and transcriptome profiling of a unicellular microalgae, Scenedesmus obliqnus mutant SO120G, with enhanced lipid production induced by heavy carbon ion beams. The lipid yield (52.5 mg L−1) of SO120G mutant were enhanced 2.4 fold compared with that of the wild strain under the nitrogen deficient condition. In addition, the biomass and growth rate were 57% and 25% higher, respectively, in SO120G than in the wild type, likely owing to an improved maximum quantum efficiency (Fv/Fm) of photosynthesis. As for the major pigment compositions, the content of chlorophyll a and carotenoids was higher in SO120G than in the wild type. The transcriptome data confirmed that a total of 2077 genes with a change of at least twofold were recognized as differential expression genes (DEGs), of which 1060 genes were up-regulated and 1017 genes were down-regulated. Most of the DEGs involved in lipid biosynthesis were up-regulated with the mutant SO120G. The expression of the gene involved in the fatty acid biosynthesis and photosynthesis of SO120G was upregulated, while that related to starch metabolism decreased compared with that of the wild strain. This work demonstrated that heavy-ion irradiation is an promising strategy for quality improvement. In addition, the mutant SO120G was shown to be a potential algal strain for enhanced lipid production. Transcriptome sequencing and annotation of the mutant suggested the possible genes responsible for lipid biosynthesis and photosynthesis, and identified the putative target genes for future genetic manipulation and biotechnological applications.
Highlights
Microalgae have received significant attention as potential next-generation microbiologic cell factories for biofuels
The Fv/Fm values of the colonies with a significant difference from the wild type (WT) were identified as possible photosynthesis efficiency mutants (PEMs)
Previous studies have indicated that the mutation rate of terrestrial plant materials, such as seeds, leaves and other organs ranged from 8.4% to 17.8%8,23,24 after irradiation by heavy-ion beams, which was higher than the traditional mutagenesis induced by X-ray, γ-ray, or EMS (Electro Magnetic Susceptibility)[8]
Summary
Microalgae have received significant attention as potential next-generation microbiologic cell factories for biofuels. To screen higher lipid-producing strains, heavy carbon ion beams are applied to induce a genetic mutant. This study provided the photosynthetic efficiency and transcriptome profiling of a unicellular microalgae, Scenedesmus obliqnus mutant SO120G, with enhanced lipid production induced by heavy carbon ion beams. All of these research results have implied that heavy ion irradiation may simultaneously increase biomass and lipid productivity in microalgae with improved photosynthesis activity. A S. obliqnus mutant, SO120G, with enhanced lipid production is generated using heavy-ion irradiation. An RNA-seq and transcriptome analysis of the S. obliqnus mutant, SO120G, and the wild type is conducted to elucidate the differentially expressed key genes (DEGs) involved in the lipid biosynthesis pathway
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