PhD Thesis - Sara Rivas-Lomelo
Microbial processes involved in the formation of ancient and modern phosphate sedimentary deposits
GRN Doctoral School Phd Grant - Advisors K. Benzerara (Geobio-IMPMC) & E Duprat (BIBiP-IMPMC)
Phosphorus (P) is an essential element for life and a limiting nutrient in many ecosystems (Paytan and McLaughlin, 2007; Pasek, 2008). Phosphorites (sedimentary deposits usually composed of carbonated fluoroapatite, a Ca-phosphate phase) are the main long-term sink in the biogeochemical P cycle. These rocks are heavily exploited to produce fertilizers for food crops; global reserves might be depleted in the next 50 to 100 years (Gilbert, 20093). Despite their importance, the processes involved in their formation remain poorly understood.
The deposition of phosphorites is apparently episodic though geological time, with certain periods (e.g. Paleo- and Neoproterozoic, Permian, Eocene, Miocene) being marked by intensive phosphorite formation (Cook and McElhinny, 1979; Filippelli, 2011), possibly corresponding to episodes of enhanced P input from the continents to the oceans linked with major climate global changes in the Earth history (Follmi, 1996; Papineau, 2010). The understanding of the formation of ancient and modern phosphate sedimentary deposits, in relation with the biogeochemical P cycle, constitutes a major environmental issue. It is now well recognized that microorganisms are involved in the P cycle, by their ability to actively store (as intracellular polyphosphates, Poly-P) or release inorganic phosphate (Pi or orthophosphate H3PO4). Pi is subsequently available for the biosphere or trapped by the biomineralization of mineral phases such as calcium or iron phosphates (or other metals e.g., Pb, Cr, U…). Yet, the microbial molecular processes involved in the phosphatogenesis, their evolution over geological time, and their relationships to the environmental conditions remain unknown.
We aim to establish a biogeochemical model of the formation of phosphate deposits. Our objectives are to identify and detail the microbial molecular processes involved in the formation of phosphate deposits, as part of the environmental phosphorus cycle. We focus at first on an analytical characterization (enzymatic assays, quantification of
different P species, microscopy) of environmental samples and cultures of microorganisms isolated from different depths in the water column of Lake Pavin (Massif Central, France). This is a meromictic, permanently stratified lake, with anoxic deep waters in which iron phosphates are currently form. (Michard et al., 1994, Viollier et al., 1997; Cosmidis et al., 2014)
1 Paytan A. and McLaughlin K. (2007) Chemical reviews 107:563-576.
2 Pasek M.A. (2008) PNAS 105(3):853-858.
3 Gilbert N. (2009) Nature 461:716-718.
4 Cook P.J., and McElhinny M.W. (1979) Econ. Geol., 74:315–330.
5 Filippelli G.M. (2011) Chemosphere, 84:759-766.
6 Follmi K. (1996) Earth-Sci. Rev., 40:55-124.
7 Papineau D. (2010) Astrobiology, 10:165-181.
8 Michard G. et al. (1994) Chemical Geology 115:103-115.
9 Viollier E. et al. (1997) Chemical Geology 142:225-241.
10Cosmidis J. et al. (2014) Geochimica et Cosmochimica Acta 126:78-96.
La pression pour contrôler le dopage électronique
Le contrôle du dopage dans les semi-conducteurs est à la base du fonctionnement des dispositifs électroniques actuels, constitués de structures hybrides MOS (métal, oxyde, semi-conducteur). L’évolution de ces structures est cependant limitée par le choix restreint des matériaux compatibles avec le silicium...
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Geobio Team @ IMPMC
The Geobio Team @ IMPMC brings together :
- 10 permanent members
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- 6 PhD students