The combined effect of nitrogen deprivation and overexpression of malic enzyme gene on growth and lipid accumulation in Phaeodactylum tricornutum

Oleaginous microalgae have great application potential in the field of bioenergy. Increasing the biomass and lipid productivity of microalgae is beneficial to realize such potential. In this study, to explore the effect of overexpression of malic enzyme (ME) gene on the growth and lipid productivity in the diatom Phaeodactylum tricornutum, the transformant (overexpression of ME) was cultivated under nitrogen deprivation and normal condition. The biomass of the transformant was higher significantly than that of the wild type (WT) both under nitrogen deprivation and normal condition. This suggested that overexpression of malic enzyme gene stimulated the growth in P. tricornutum. The lipid content of the transformant under normal condition increased significantly compared with that of WT under nitrogen deprivation. The transformant strain exhibited further increase in lipid accumulation subjected to nitrogen deprivation. Upon nitrogen deprivation, lipid productivity of the transformant was significantly increased by 87.02% compared with that of the WT strain. These findings suggested that ME overexpression increased the production of NADPH, further stimulated the growth and lipid synthesis, resulting in enhancing lipid productivity in the transformant under nitrogen deprivation. This ME overexpression-nitrogen deprivation cultivation pattern provided a new route to enhance biodiesel production in microalgae.