PhD defence: Antonina Karakostova

The title of the PhD thesis is: Transport Engineering in Microalgae for Studying and Controlling Carbon Flux

Abstract:

In the last decades, there has been an increasing interest in domestication of microalgae for production of nutrient-rich biomass and valuable compounds of plant cell origin. However, microalgae-based bioprocesses are hampered by low yields and associated high production costs.

The research presented in this PhD thesis explores the potential of trophic conversion via transport engineering for targeting exogenous reduced carbon towards enhancing biomass production. By expressing a glucose transporter from higher plants in the plasma membrane of the model green microalga Chlamydomonas reinhardtii, we enabled it to grow heterotrophically on glucose in dark, and to also utilize assimilated glucose for enhanced biomass formation in light. We achieved the highest to-date cell density obtained for a trophically converted C. reinhardtii growing on glucose. Characterization of pigment and neutral lipid content and a comparative time-resolved transcriptomic dataset elucidated led us to build a model describing C. reinhardtii’s adaptive response to a novel carbon source. Excitingly, we show that strong influx of carbon into the cell leads to increased production of desirable storage compounds, the triggering of fermentative pathways for anaerobic breakdown of glucose-derived products, and a multitude of induced nutrient starvation responses at the transcript level. Additionally, we investigated the spatial organization of metabolic networks involved in glucose metabolism within the cell at the sub-organellar level and found evidence of strict spatial micro-compartmentation of two enzymes of the glycolytic chain and a putative plastidic hexose transporter.

The research presented in this thesis asserts transport engineering as a viable strategy for development of microalgal strains with biotechnological potential and can in the future inform similar approaches in other microalgal species. The novel strain will serve as a stepping-stone for downstream optimization to further enhance biomass and break through the yield barrier. Furthermore, it presents an attractive model for studying cell metabolism under carbon-unlimited conditions.

Supervisor: Associate professor Hussam Nour-Eldin, Department of Plant and Environmental Sciences

Assessment commitee: 

Professor Poul Erik Jensen (chairperson), Department of Food Science, University of Copenhagen, Denmark

Professor Olaf Kruse, Scientific Director Center for Biotechnology (CeBiTec), Bielefeld Univeristy, Germany

Professor Steve Mayfield, Director of California Center for Algae Biotechnology, UC San Diego, US

The PhD defence will be followed by a reception in H117, Thorvaldsensvej 40, 1. floor entrance 2-4!