SEMINARIO Dr. Marie Catherine SFORNA: "Arsenic-metabolizing microorganisms on Primitive Earth"


Title: Arsenic-metabolizing microorganisms on Primitive Earth

Speaker: Marie Catherine Sforna
Affiliation: Geobiosphere Actuelle et Primitive, IPGP, Paris -
Now at Dipartimento Scienze Chimiche e Geologiche, UNIMORE

Date & Time: Thursday, November 13th 2014,– h : 16:00
Venue: DSCG, P.zza St. Eufemia 19, II floor, Aula M, Modena

Host: Daniele Brunelli

Abstract: Metals are widely used by all microorganisms and could act as indicators of past microbial activity in the rock record when abiotic processes are reliably excluded. Stromatolites, ubiquitous in the rock record for the last 3.5 Ga, are excellent targets for investigating the behavior of trace metals during these processes. This study focuses on 2.7 Ga old stromatolites from the Tumbiana Formation (Western Australia) and on modern stromatolites from the Bahamas.
We characterized at different scales (cm² to nm²) the metal distribution by SR-µXRF and SR-µXANES, and associated organic materials by Raman spectroscopy and CLSM. A statistical treatment by Principal Component Analysis provides constraints on the origin and remobilization of metals in modern and ancient microbial mats.
Results show that the distribution of metals in stromatolite is mainly governed by passive processes in the living mats and by remobilization and concentration through diagenesis and metamorphism during burial. Cell-like organic globules were identified in both modern and Archean stromatolites. They present significant enrichments in arsenic, with no, or only negligible contributions of other metals (specifically Fe) and are interpreted as biological in origin. Although phylogenetic studies indicate that microbial arsenic metabolism is ancient and As-based metabolisms are described in different environments, it is the first time that a link between As-based metabolism and the primitive Earth is clearly identified.