[3dem] Postdoc Announcement: "Cryo-TEM study of intracellular biomineralization of calcium carbonates by cyanobacteria"

[Karim benzerara]

Hello,

here is a postdoc annoucement for 2 years in Paris funded by an ERC grant.
(pdf file attached)

Sincerely,

Karim Benzerara


Cyanobacteria are among the most important bacteria involved in the
interactions between the geosphere and the biosphere. They are
photosynthetic bacteria that appeared more than 2.3 billion years ago. It
is usually assumed that by fixing CO2 in the form of organic carbon, they
raise the pH of the environment and induce precipitation of calcium
carbonates. They may thus have had a major role in the formation of
carbonate rocks throughout Earth’s history. Despite the geochemical
importance of cyanobacteria mediated
CaCO3 biomineralization, the mechanistic details of this process are yet
poorly understood. Recently, we discovered the existence of an
early-diverging cyanobacterial species, Candidatus Gloeomargarita
lithophora, which form intracellular carbonates (Couradeau et al., 2012,
Science. See also: http://www2.cnrs.fr/presse/communique/2589.htm). More
recently, we discovered several additional species doing that as well
(Benzerara et al. in rev. in PNAS).
This challenges all existing models of cyanobacterial calcification which
used to assume that carbonate precipitation by cyanobacteria was
exclusively extracellular and was thus not controlled by the cells. We know
very little about the mechanisms involved in this capability to produce
intracellular carbonates. The study of the ultrastructure of such strains
will be crucial to understand their carbon metabolism and how they form
minerals.
The present job will consist in studying the ultrastructure of these
particular cyanobacteria that are cultured in the laboratory. Different
lines of research are considered (1& 2 have priority; 3 & 4 optional): 1)
using Cryo-Electron MicroscOpy of VItreous Sections (CEMOVIS) to describe
the ultrastructure of cyanobacteria forming intracellular carbonates vs.
cyanobacteria not forming intracellular carbonates; 2) applying on these
cryo-sections advanced chemical analyses such as those provided by electron
energy loss spectroscopy (EELS); 3) performing cryo-EM tomography on these
strains; 4) using synchrotron-based xray microscopy (STXM) under cryo
conditions to get additional information on carbon speciation.
The candidate should have a strong experience in microscopy and ideally in
cryo- TEM. She/he should have skills for working in a team and supervising
PhD students, conducting her/his research autonomously and communicate
her/his results in English.
The funding is for at least 2 years. It is provided by a Starting Grant
from the European Research Council (ERC). Employment will be arranged by
the administration of CNRS. The position can open as soon as June, 1st 2014
and preferably no later than the end of 2014 (it will stay open until a
suitable candidate is found). Candidates should send a detailed CV with a
letter of motivation explaining the motivations for this job to Karim
Benzerara, Geobiology group at the Institute of Mineralogy, Material
Physics and Cosmochemistry; karim.benzerara at impmc.upmc.fr
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