Heterologous expression of HUP1 glucose transporter enables low-light mediated growth on glucose in Phaeodactylum tricornutum

Microalgae are in the focus of research and industry because of their potential as high-value substance producers. Especially diatoms and within this group Phaeodactylum tricornutum are of high interest as biofactory, for e.g. synthesizing high amounts of fucoxanthin or as important source for omega-3 fatty acids. As model organism P. tricornutum can be used for genetic engineering. Here we showed the potential of P. tricornutum as efficient biofactory under mixotrophic conditions, combining the advantages of hetero- and phototrophic growth. We expressed the hexose uptake protein (HUP1) from the Chlorophyte Chlorella kessleri under the control of the lightinducible promoter fcpA or the nitrate reductase promoter. Only in case of fcpA significant overexpression could be demonstrated. With an in situ localization study, we demonstrated that the N-terminal sequence of the heterologous HUP1 protein is sufficient for insertion in the ER, whereas only the full-length protein is correctly targeted to the plasma membrane. The heterologous expression of HUP1 enables the cells to take up glucose, leading to increased biomass, especially when grown under low light intensities. The results demonstrate the capability of P. tricornutum to grow more efficiently using glucose and shed light on the targeting pathway of plasma membrane transporters.

Automated summary

This study demonstrates the potential of Phaeodactylum tricornutum as an efficient biofactory under mixotrophic conditions, by expressing the HUP1 protein to enable glucose uptake and increase biomass. The study also provides insights into the targeting pathway of plasma membrane transporters.