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Project Progress

We have examined the chemical and microbiological composition of groundwater Fe seep material from Tuscaloosa, AL and weathered basalt materials from Box Canyon, ID. Significant numbers of both Fe(III)-reducing and Fe(II)-oxidizing microorganisms were detected in both materials, which suggests the potential for microbially-catalyzed Fe redox cycling. Several highly-purified Fe(III)-reducing and Fe(II)-oxidizing cultures have been obtained and are currently being physiologically and phylogenetically characterized. A 16S rRNA gene clone library indicated the presence of a variety of lithotrophic ammonium- and Fe(II)-oxidizing phylotypes in the Fe seep community, and additional clone libraries have been constructed for both the Fe seep and weathered basalt communities. Incubation of amorphous Fe(III) oxide-rich seep material under anaerobic conditions demonstrated the potential for rapid Fe(III) oxide reduction. These results are conceptually consistent with previous studies with cocultures of Fe(III)-reducing and Fe(II)-oxidizing bacteria, and suggest that tight coupling of microbial Fe oxidation and reduction takes place in the seep environment. Similar results were obtained with the weathered basalt materials, which are unique in that they contain magnetic Fe(III) oxide phases (presumably maghemite), which appear to be converted to the magnetite during microbial reduction. The Fe seep and weathered basalt systems provide models for how microbially-catalyzed Fe redox cycling could take place in subsurface Martian environments where reduced fluids/solids contact oxygen-bearing water or water vapor. Simultaneous operation of Fe(III) oxide reduction and Fe(II) oxidation reactions could in principle support a self-sustaining Fe redox cycle-based microbial life system that could be sustainable over geological time scales.