HR: 15:10h
AN: B52C-05    [PDF]
TI: High Spatial Resolution Study of Microbe-Carbonate-Silicate Interfaces by FIB and TEM
AU: * Benzerara, k
EM: benzerar@lmcp.jussieu.fr
AF: LMCP, Case 115 4 Place Jussieu, Paris, 75252 France
AU: Menguy, N
EM: menguy@lmcp.jussieu.fr
AF: LMCP, Case 115 4 Place Jussieu, Paris, 75252 France
AU: Guyot, F
EM: guuyot@lmcp.jussieu.fr
AF: LMCP, Case 115 4 Place Jussieu, Paris, 75252 France
AU: Vanni, C
EM: vanni@univ.u-3mrs.fr
AF: CP2M, Faculte Saint Jerome, Marseille, 13397 France
AU: Gillet, P
EM: pgillet@ens-lyon.fr
AF: Laboratoire des sciences de la Terre, ENS Lyon, Lyon, 69007 France
AB: High resolution transmission electron microscopy (HRTEM), chemical micro-analysis (EDX) and electron energy loss spectroscopy (EELS) are among the most powerful analytical techniques for studying microbe-mineral interactions, allowing to observe the microbe-mineral interface at almost the angstrom scale, to evidence transformations of the mineral structure and chemical alterations at the nanometer scale. However, the samples must be very thin and only a small area can be investigated. A key limitation for using this technique is thus to prepare natural geomicrobiological samples which combine hard minerals, preventing use of ultramicrotomy, with soft organic matter inadequate to ion milling procedures. Additionaly the areas of interest are usually restricted to few micrometer large areas which have to be selected from macroscopic samples. In this study we present two procedures : micromanipulation and FIB (Focused Ion Beam) which allow the study of microbe-mineral interfaces with TEM. The micromanipulation procedure has been presented in Benzerara et al (2003, PNAS). We have evidenced nannobacteria-like objects at the surface of the Tatahouine orthopyroxenite meteorite fallen in the tunisian desert in 1931. SEM observations suggest a complex interaction pattern between the nannobacteria-like objects, the pyroxene and microorganisms which have colonized the surface of the meteorite during its seventy years of residence on Earth. The TEM study on the very same area shows that the nannobacteria-like rods are actually well-crystallized nanometric calcite single crystals surrounded by an amorphous layer of carbonate composition. Those morphologies and structures are unusual for calcite single crystals. We discuss these observations in regard to the criteria of biogenicity i.e. biosignatures. Moreover, we examine the implications for carbonate production associated to silicate bio-weathering under aridic conditions. This work is relevant both to astrobiological and geomicrobiological issues showing that it is possible to select a microbe-mineral interface of interest at the micrometer scale, and then to prepare it for TEM observation.
DE: 0614 Biological effects
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3662 Meteorites
DE: 4803 Bacteria
DE: 4885 Weathering
SC: Biogeosciences [B]
MN: 2003 Fall Meeting