THERMOPHILIC FE(III)-REDUCING BACTERIA FROM THE DEEP SUBSURFACE - THEEVOLUTIONARY IMPLICATIONS

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