Secondary Mineral Formation Associated With Respiration of Nontronite, NAu-1 by Iron Reducing Bacteria
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS SEAFLOOR SCIENCES DIRECTORATE
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Experimental batch and miscible-flow cultures were studied in order to determine the mechanistic pathways of microbial FeIII respiration in ferruginous smectite clay, NAu-1. The primary purpose was to resolve if alteration of smectite and release of Fe precedes microbial respiration. Alteration of NAu-1, represented by the morphological and mineralogical changes, occurred regardless of the extent of microbial FeIII reduction in all of our experimental systems, including those that contained heat-killed bacteria and those in which O2, rather than FeIII, was the primary terminal electron acceptor. The solid alteration products observed under transmission electron microscopy included poorly crystalline smectite with diffuse electron diffraction signals, discrete grains of Fe-free amorphous aluminosilicate with increased AlSi ratio, Fe-rich grains, and amorphous Si globules in the immediate vicinity of bacterial cells and extracellular polymeric substances. In reducing systems, Fe was also found as siderite. The small amount of Fe partitioned to the aqueous phase was primarily in the form of dissolved FeIII species even in the systems in which FeIII was the primary terminal electron acceptor for microbial respiration. From these observations, we conclude that microbial respiration of FeIII in our laboratory systems proceeded through the following 1 alteration of NAu-1 and concurrent release of FeIII from the octahedral sheets of NAu-1 and 2 subsequent microbial respiration of FeIII.
- Geology, Geochemistry and Mineralogy
- Inorganic Chemistry