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Physiology of the dissimilatory iron-reducing isolate GS-15: Proposed name Geobacter metallireducens gen. nov., sp. nov.
Abstract
The biochemistry and bioenergetics of the dissimilatory iron-reducing bacterium GS-15, proposed name Geobacter metallireducens gen. nov., sp. nov., were studied by identifying enzymes and electron transfer components. Enzymes of the citric acid cycle were found in detergent-treated, whole-cell suspensions, and cell-free extracts while enzymes of the carbon monoxide dehydrogenase were not. This was true whether nitrate or ferric ion acted as the terminal electron acceptor. Menaquinone and cytochrome c were extracted from cells. 2-Oxoglutarate and NADPH oxidation were coupled to methyl viologen reduction. 2-Oxoglutarate also reduced clostridial ferredoxin, and evidence for ferredoxin in GS-15 is given. A soluble, low-midpoint-potential cytochrome c was obtained having 3.1 mol heme c per MW of 12900 kD. Nutritional studies indicated: (1) that growth, as measured increase in cell protein, was coupled to iron reduction with a doubling time of 33 h and a yield of 2 g of cell protein per mol acetate; (2) penicillin-G completely growth at 100 $\mu$g per ml and iron reduction did not occur in cultures with 10 $\mu$g per ml; (3) pimelate was identified as a growth substrate; (4) cells contained in vivo hydrogenase activity and iron reduction was inhibited by hydrogen at high concentration. These data were used to construct a model for the transfer of electrons from the citric acid cycle to the terminal electron acceptor ferric iron. The low growth rate and yield of GS-15 is discussed with regards to energy conservation in this model for electron transfer. The presence of the citric acid cycle, 2-oxoglutarate synthase, menaquinone, and a multiheme cytochrome c are all consistent with members of the delta subgroup of the proteobacteria. Corroborating 16S rRNA sequence and lipid analysis data obtained elsewhere are included in the appendix. The relation of this iron-reducing bacterium to the sulfur- and sulfate-reducing bacteria is discussed. The similarities and differences with Shewanella putrefaciens, another dissimilatory iron-reducing bacterium, are also presented.
Subject Area
Microbiology
Recommended Citation
Champine, James Edward, "Physiology of the dissimilatory iron-reducing isolate GS-15: Proposed name Geobacter metallireducens gen. nov., sp. nov." (1993). Doctoral Dissertations Available from Proquest. AAI9316631.
https://scholarworks.umass.edu/dissertations/AAI9316631