K-094. A Unique Response Regulator of a Two-Component System Involved in a Variety of Cellular Processes in Geobacter sulfurreducens

T. Ueki, A. Murchie, D. R. Lovley;
Univ. of Massachusetts, Amherst, MA.

The regulation of gene expression in Geobacter sulfurreducens is being intensively investigated because G. sulfurreducens is closely related to the Geobacter species that are important in the anaerobic bioremediation of organic and metal contaminants in the subsurface and because G. sulfurreducens is capable of generating high current densities in microbial fuel cells. Therefore, there is particular interest in mechanisms regulating extracellular electron transfer and the ability to associate with surfaces. The G. sulfurreducens genome encodes an unusually large number of proteins belonging to the histidine kinase and the response regulator of the two-component His-Asp phosphorelay system, which is a major device in bacterial signal transduction during responses to environmental changes. This may reflect the necessity of G. sulfurreducens for adaptation to various growth conditions in subsurface environments. The response regulator designated Grr2 was found to have a typical receiver domain at the N-terminus, but two unique domains at the C-terminus. One of these domains shows no homology to any known proteins and is very acidic. The other exhibits similarity to the C-terminal end of response regulators from other Geobacter species and other δ-Proteobacteria. A strain in which the gene for Grr2 was deleted grew slower and had lower cell densities than the wild-type strain in medium with acetate as the electron donor and fumarate as the electron acceptor. Whereas wild-type cells grew planktonically under these conditions, the mutant formed extensive biofilms on the glass culture tubes. The mutant was also defective in Fe(III) reduction. Mutant cells were more elongated than the wild-type cells, indicating that cell division was impaired in the mutant. Whereas wild-type cells could grow with hydrogen as the electron donor, the mutant cells could not. These results suggest that Grr2 is involved in a variety of cellular processes in G. sulfurreducens. Genome-scale analysis of gene transcript levels with microarrays is underway to further understand the broad impact of this two-component regulatory system.