Thermophilic Fe(III)-Reducing Bacteria from the Deep Subsurface: The Evolutionary Implications

Thermophilic (45° to 75°C) bacteria that reduce amorphous Fe(III)-oxyhydroxide to magnetic iron oxides have been discovered in two geologically and hydrologically isolated Cretaceous- and Triassic-age sedimentary basins in the deep (>860 meters below land surface) terrestrial subsurface. Molecular analyses based on 16 S ribosomal RNA (rRNA) gene sequences revealed that some of these bacteria represent an unrecognized phylogenetic group of dissimilatory Fe(III)-reducing bacteria. This discovery adds another dimension to the study of microbial Fe(III) reduction and biogenic magnetism. It also provides examples for understanding the history of Fe(III)-reducing microorganisms and for assessing possible roles of such microorganisms on hot primitive planets.