Sébastien Zappa
Postdoctoral Researcher Associate

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Curriculum vitae (English)
Curriculum vitae (French)

The purple photosynthetic bacteria group represents a good model to study bioenergetic metabolism as a function of environmental conditions. Indeed, they can switch from a photosynthetic to a respiratory metabolism, depending on both light and redox conditions. This “switch” involves a tremendous amount of genes and proteins, from the sensing of a light/redox signal, to the activation/repression of a metabolic pathway. As a result, this complexity, observed in simple and versatile organisms, is of great interest to be studied from both a genetic and a biochemical approaches: on the one hand by investigating the levels of gene expression depending on environmental conditions; on the other by isolating signal receptor proteins and transcription factors and studying them in vitro. My previous post-doctoral project consisted in studying bacteriophytochromes from photosynthetic bacteria Bradyrhizobium sp. and Rhodopseudomonas palustris , as well as their associated regulators. These photoreceptors and regulators are involved in the regulation of the synthesis of the photosystem, giving to the cell a tight control of the level of reaction center, light harvesting complex I and II. My present project deals with the control of heme level in the cell, using the bacterium Rhodobacter capsulatus as a model. As heme and its derivative bacteriochlorophyll are involved in biochemical fundamental processes, such as respiration and photosynthesis, it appears vital for the cell to exert a tight regulation of the balance of heme vs. bacteriochlorophyll concentrations in order to respond to the bioenergetic metabolism needs triggered by the environmental conditions. Indeed, several transcription factors involved in heme synthesis regulation have been found so far, including HbrL, the one my project is more focused on. This transcription factor is being studied from both a genetic and a biochemical approach, aiming at finding out the genes it regulates as well as its structure and mechanism of action.