A possible role of Fe(Ⅱ)-oxidizing photoautotrophic bacteria in the formation of ancient Fe(Ⅲ)-mineral deposits (banded iron formations)

摘要

To interpret putative Fe-isotope "biosignatures" in ancient rocks, it is necessary to define and understand microbial Fe-metabolism at a molecular level. Here, we have characterized the substrates and products of photoautotrophic Fe(Ⅱ)-oxidation and investigated the role of free organic ligands in Fe(Ⅲ) release by the cells. Our results suggest that Fe(Ⅲ) is released by the bacteria in a dissolved form as an inorganic aqueous complex and/or as a colloidal aggregate prior to mineral precipitation. The implication of these results for the interpretation of Fe-isotope fractionation measured for this class of bacteria is that equilibrium processes involving free biological ligands do not account for the observed fractionation.