Thesis presented May 06, 2024

Abstract:
The symbiotic origin of the chloroplast in eukaryotes is heralded as one of the most important biological innovations in the evolution that led to the diversification of plants and microalgae. The paradigm suggests that metabolic control of the host cell was a key step to accommodate and domesticate its captured microalgae before their genetic integration and transformation into a chloroplast. Yet, this has to be demonstrated on contemporaneous photosymbioses, which are fundamental models to investigate the mechanisms by which hosts engineer intact microalgal cells.
In aquatic ecosystems, photosymbioses between heterotrophic hosts and microalgae are widespread and ecologically important. The freshwater photosymbiosis between the host Paramecium bursaria (ciliate) and the green alga Chlorella sp is the only unicellular eukaryotic photosymbiosis where i) partners can be cultured in symbiosis or separately, ii) genomes of both partners are sequenced, iii) and symbiosis can be reestablished where new Chlorella cells are captured and enclosed in a host-derived vacuole (symbiosome). This symbiosome is a key functional interface between the host and the microalgae where metabolic exchanges and host control can occur. However, the molecular players, such as transporters and pumps, remain to be described.
The PhD student will study the cultured Paramecium-Chlorella symbiosis as a model to decipher key functional mechanisms of the host control over its microalgae.

Keywords:
Photosymbiosis, High-resolution imaging, Fluorescence microscopy, Microalgae, Proteomics