Electron Microscopic Characterization of Mineral-Microbe Interactions

Abstract

Microbes are capable of reducing structural Fe(III) in minerals and promoting the formation of amorphous or crystalline solid phases as byproducts. The extent and rate of bioreduction depends on a number of factors, including mineral surface area, sorption capacity of mineral surfaces for Fe, the presence or absence of chelating agents (i.e., AQDS and humic acids), complexing agents, electron donor or acceptor, and type of microorganisms [1]. Microbial reduction of Fe(III) in minerals often results in mineral dissolution and neoformation of biogenic minerals [2]. Few attempts have been made to show the dynamic nature of microbial-mediated mineral reactions, especially at the microand nanoscale. Here we present evidence for formation of non-stoichiometric mineral phases as a result of microbial reduction of Fe(III) of magnetite. These mineral phases are important in geological processes such as metal sorption, nutrient cycling, and contaminant degradation. More importantly, if these nonstoichiometric minerals can be used as a characteristic of biologically induced solid phases, they may be used as a biosignature for the search for evidence of ancient terrestrial and extraterrestrial life.