Abstract
BackgroundNumerous studies have shown that stress induction and genetic engineering can effectively increase lipid accumulation, but lead to a decrease of growth in the majority of microalgae. We previously found that elevated CO2 concentration increased lipid productivity as well as growth in Phaeodactylum tricornutum, along with an enhancement of the oxidative pentose phosphate pathway (OPPP) activity. The purpose of this work directed toward the verification of the critical role of glucose-6-phosphate dehydrogenase (G6PDH), the rate-limiting enzyme in the OPPP, in lipid accumulation in P. tricornutum and its simultaneous rapid growth rate under high-CO2 (0.15%) cultivation.ResultsIn this study, G6PDH was identified as a target for algal strain improvement, wherein G6PDH gene was successfully overexpressed and antisense knockdown in P. tricornutum, and systematic comparisons of the photosynthesis performance, algal growth, lipid content, fatty acid profiles, NADPH production, G6PDH activity and transcriptional abundance were performed. The results showed that, due to the enhanced G6PDH activity, transcriptional abundance and NAPDH production, overexpression of G6PDH accompanied by high-CO2 cultivation resulted in a much higher of both lipid content and growth in P. tricornutum, while knockdown of G6PDH greatly decreased algal growth as well as lipid accumulation. In addition, the total proportions of saturated and unsaturated fatty acid, especially the polyunsaturated fatty acid eicosapentaenoic acid (EPA; C20:5, n-3), were highly increased in high-CO2 cultivated G6PDH overexpressed strains.ConclusionsThe successful of overexpression and antisense knockdown of G6PDH well demonstrated the positive influence of G6PDH on algal growth and lipid accumulation in P. tricornutum. The improvement of algal growth, lipid content as well as polyunsaturated fatty acids in high-CO2 cultivated G6PDH overexpressed P. tricornutum suggested this G6PDH overexpression-high CO2 cultivation pattern provides an efficient and economical route for algal strain improvement to develop algal-based biodiesel production.
Highlights
Numerous studies have shown that stress induction and genetic engineering can effectively increase lipid accumulation, but lead to a decrease of growth in the majority of microalgae
The glucose-6-phosphate dehydrogenase (G6PDH) overexpressed lines showed enhanced lipid accumulation of around 38% compared with the G6PDH silencing strains. These results suggested that overexpression of G6PDH stimulated P. tricornutum lipid accumulation, while knockdown of G6PDH resulted in a significant decrease in lipid content under CO2 cultivation
Following Glucm treatment, the wild-type cells showed a significant decrease in NADPH concentration of approximately 49.83% under normal cultivation and 37.49% under high-CO2 cultivation (P < 0.01), compared to wild-type cells without inhibitor treatment (Fig. 2c). These results suggested that the addition of Glucm, similar to silencing G6PDH, markedly reduced the transcriptional abundance of G6PDH and inhibited its activity led to the decrease in algal growth, lipid accumulation and fatty acids synthesis irrespective of whether the algal cells were cultured with normal or high-CO2 cultivation
Summary
Numerous studies have shown that stress induction and genetic engineering can effectively increase lipid accumulation, but lead to a decrease of growth in the majority of microalgae. The marine diatom Phaeodactylum tricornutum is wellknown for its high photosynthesis efficiency, rapid growth rate, and abundant lipids (especially unsaturated fatty acids), fucoxanthin and protein yield. These excellent properties make it promisingly for industrial microalgae production, and one of the most widely studied model diatoms in terms of ecology, physiology, biochemistry and molecular biology [1, 2]. To enhance lipid productivity in P. tricornutum, numerous studies have been carried out including oleaginous microalgal species screening and microalgal domesticated [5,6,7,8,9,10,11]. Exploring for an improvement of both lipid accumulation and growth rate is of great importance in microalgae production
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