Isotopic and mineralogical approach of Fe sulfide biomineralization by sulfate reducing bacteria

PhD Arnaud Duverger (advisors: V. Busigny-IPGP, J. Miot – ENS/IPGP grant)

Sulfate reducing bacteria (SRB) may have played a major role during Earth history, through the connection of C, Fe and S biogéochemical cycles. Fe sulfides are widespread in the fossil record and are keystones to understand the evolution of paleoredox conditinos at Earth surface. We however need strong biogenicity criteria to discriminate Fe sulfides formed through abiotic vs. microbial pathways. The goal of this PhD thesis is to elucidate the mechanisms of Fe sulfide biomineralization by model SRB, depending on culture conditions. Biomineralization products will be characterized down to the atomic scale using a combination of spectroscopy and microscopy methods. Fe and S isotopic compositions will be determined in order ot calculate isotopic fractionations upon sulfate reduction and iron sulfide precipitation.

TEM image of sulfate reducing bacteria and associated Fe sulfides (mackinawite).