HYPERBIOMIN

Hydrothermal deep-sea vents are often iron- and sulfur-rich anaerobic systems. Whereas FeS2 pyrite is abiotically formed in the interior of chimneys at high temperatures (> 250°C), a major stock of FeS2 (pyrite and marcasite) is also produced in the cooler middle layers of the chimneys at lower temperatures (80°C) biosphere to biogeochemical cycles and regulations, it is now time to progress in the mechanistic elucidation of those high temperature biomineralization phenomena. Thermococcus kodakarensis will be the organism of choice for HYPERBIOMIN project, since many interesting results have already been obtained for this strain and in our laboratory and genetic tools for this hyperthermophilic archaeon are well established. HYPERBIOMIN project addresses three main questions: (1) What are the physiological conditions of the cells and physico-chemical parameters of the life medium which influence and control the rates of iron biominerals produced by Thermococcales? (2) What are the biological entities and genes implied in the Thermococcales biomineralization mechanism? (3) What are the adaptive strategies developed by hyperthermophiles to influence and cope with their highly mineralized high temperature environments? To answer these questions, the project will follow three complementary approaches: (1) The first approach consists in determining and analyzing quantitatively the iron-sulfide minerals produced under different physico-chemical conditions mimicking the fluctuating environment of hydrothermal chimneys. I have so far limited the biomineralization studies at the optimal growth parameters of Thermococcales strains. In collaboration with a PhD and a master student, we will determine the impacts of temperature and pH but also of the metabolic shifts of Thermococcales (H2S production vs H2 production) induced by environmental conditions on the composition, structure and properties of iron minerals formed during the biomineralization process. (2) The second approach deals with the exploration of the molecular mechanism of biomineralization by Thermococcales. To date, no information is available about the relationships between production of biominerals and putative related-genes. We will detect and identify molecular partners involved in T. kodakarensis biomineralization mechanism focusing first on genes encoding ferritins and iron transporters because of their potential importance in iron biomineralization processes. I will then explore the genes involved in synthesis and expression of membranes vesicles which have been reported to contribute to the formation of pyrite by Thermococcales. (3) In a third approach, I will investigate the significance of those biomineralization processes for the adaptation mechanisms of Thermococcales and Methanococcales in the hydrothermal ecosystem. Experiments involving both T. kodakarensis and Methanocaldococcus jannaschii in presence and absence of minerals will be carried out for deciphering adaptive responses to the harsh hydrothermal environment and the potential role of minerals in the adaptation of life in this simplified but yet complex and realistic ecosystem.