PHYLOGENETIC ANALYSIS OF DISSIMILATORY FE(III)-REDUCING BACTERIA

Evolutionary relationships among strictly anaerobic dissimilatory Fe(I II)-reducing bacteria obtained from a diversity of sedimentary environ ments were examined by phylogenetic analysis of 16S rRNA gene sequence s. Members of the genera Geobacter, Desulfuromonas, Pelobacter, and De sulfuromusa formed a monophyletic group within the delta subdivision o f the class Proteobacteria, On the basis of their common ancestry and the shared ability to reduce Fe(III) and/or S-0, we propose that this group be considered a single family, Geobacteraceae. Bootstrap analysi s, characteristic nucleotides, and higher-order secondary structures s upport the division of Geobacteraceae into two subgroups, designated t he Geobacter and Desulfuromonas clusters. The genus Desulfuromusa and Pelobacter acidigallici make up a distinct branch within the Desulfuro monas cluster, Several members of the family Geobacteraceae, none of w hich reduce sulfate, were found to contain the target sequences of pro bes that have been previously used to define the distribution of sulfa te-reducing bacteria and sulfate-reducing bacterium-like microorganism s. The recent isolations of Fe(III)-reducing microorganisms distribute d throughout the domain Bacteria suggest that development of 16S rRNA probes that would specifically target all Fe(III) reducers may not be feasible, However, all of the evidence suggests that if a 16S rRNA seq uence falls within the family Geobacteraceae, then the organism has th e capacity for Fe(III) reduction. The suggestion, based on geological evidence, that Fe(III) reduction was the first globally significant pr ocess for oxidizing organic matter back to carbon dioxide is consisten t with the finding that acetate-oxidizing Fe(III) reducers are phyloge netically diverse.