Date : 09/01/2012

Internship proposal for : Master 1

Laboratory
Institut de Minéralogie et de Physique des Milieux Condensés et Ecologie/systématique et Evolution
UMR 7590 CNRS-UPMC-IRD
4 Place Jussieu
75005 Paris
Website
Main discipline : Geology / Geophysics
Lab director : Bernard Capelle

Mentor
Dr Karim Benzerara
email : This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
phone : +33 1 44 27 75 42

Subjects
1.: cyanobacteria
2.: biomineralization
3.: carbonates

Tools and methodologies
1.: Transmission Electron Microscopy
2.: Scanning Electron Microscopy
3.: Cultures and eifluorescent microscopy

Summary of lab's interests
Our Geomicrobiology group studies the interactions between microorganisms and minerals. Microorganisms can form minerals (biomineralization). This has multiple implications: in environmental science since this process can lead to immobilization of pollutants; in geology/paleontology since this process can fossilize cells which are then rpeserved for millions/billions of years in the geological record; ecology since mineral precipitation might be a stress or might offer some advantages to the cells; finally for material science, since minerals formed by life might have unique properties that are interesting to mimick in order to design new materials. We are interested in the fundamental mechanisms of these interactions and the diverse implications.

Summary of project
Cyanobacteria are among the most important bacteria involved in the interactions between the geosphere and the biosphere. Indeed, they had a pivotal role on several global geochemical cycles throughout Earth's history, including C, N and O. In particular, they have been contributing significantly to the global carbon cycle by assimilating CO2 to organic carbon and by triggering CaCO3 precipitation through photosynthesis. I, there is t has been observed that there is a huge difference in timing between first cyanobacteria and first microfossils of calcified cyanobacteria. This has been classically called the 'Precambrian Enigma'. To solve this paradox, we crucially need a better knowledge of the precise mechanisms involved in calcification in modern cyanobacteria and an assessment of how diverse cyanobacteria may use diverse biomineralization pathways. We recently discovered deep-branching cyanobacteria that form intracellular Ca-Mg-Sr-Ba carbonates. So far, calcification by cyanobacteria had been considered exclusively as extracellular. The existence of intracellularly calcifying cyanobacteria thus significantly modifies our view on the past and modern role of cyanobacteria in the formation of carbonate deposits and the degree of control they achieve on this geochemically important process. We know very little on these cyanobacteria that we can culture in the laboratory. The goal of this internship will be to get first order information on their biology (e.g., how fast do they form minerals? do they raise the solution pH? Do they dissolve or form mineral inclusions in the dark? Are they still metabolically active when precipitates form?) and the chemical composition of the carbonate mineral they form. The candidate will use diverse tools such as (but not exclusively): transmission electron microscopy, scanning electron microscopy, epifluorescent microscopy (with pH and calcium probes), cultures; possibly synchrotron techniques. Basic knowledge in Earth sciences and/or microbiology and/or electron microscopy appreciated but not mandatory.