ISOLATION OF GEOBACTER SPECIES FROM DIVERSE SEDIMENTARY ENVIRONMENTS

In an attempt to better understand the microorganisms responsible for Fe(III) reduction in sedimentary environments, Fe(III)-reducing microo rganisms were enriched for and isolated from freshwater aquatic sedime nts, a pristine deep aquifer, and a petroleum-contaminated shallow aqu ifer. Enrichments were initiated with acetate or toluene as the electr on donor and Fe(III) as the electron acceptor. Isolations were made wi th acetate or benzoate. Five new strains which could obtain energy for growth by dissimilatory Fe(III) reduction were isolated. All five iso lates are gram-negative strict anaerobes which grow with acetate as th e electron donor and Fe(III) as the electron acceptor, Analysis of the 16S rRNA sequence of the isolated organisms demonstrated that they al l belonged to the genus Geobacter in the delta subdivision of the Prot eobacteria. Unlike the type strain, Geobacter metallireducens, three o f the five isolates could use H-2 as an electron donor for Fe(III) red uction, The deep subsurface isolate is the first Fe(III) reducer shown to completely oxidize lactate to carbon dioxide, while one of the fre shwater sediment isolates is only the second Fe(III) reducer known tha t can oxidize toluene. The isolation of these organisms demonstrates t hat Geobacter species are widely distributed in a diversity of sedimen tary environments in which Fe(III) reduction is an important process.