H-071. RpoN Targets in Geobacter sulfurreducens

J. Krushkal¹, C. Leang², M. Puljic¹, R. M. Adkins¹, D. R. Lovley²;
¹Univ. of Tennessee Hlth. Sci. Ctr., Memphis, TN, ²Univ. of Massachusetts, Amherst, MA.

Geobacter sulfurreducens is a pure culture representative for a group of species, Geobacteraceae, which participate in environmental bioremediation and harvesting of electric energy. We used computational sequence analysis to identify promoter sequence elements of an alternative sigma factor, RpoN (σ⁵⁴), and investigated its target operons. The highest scoring RpoN-regulated promoter, most similar to conserved RpoN-regulated sequences from other bacteria, was located upstream of an operon containing a gene for flagellar transcription factor FliA (σ²⁸) and other genes for flagellar biosynthesis. This operon was significantly downregulated in a strain overexpressing RpoN, suggesting competition between RpoN and other sigma factors. Many other genes related to flagellar function and pili production also have upstream RpoN-regulated promoters. This suggests that RpoN controls many aspects of flagellar and pili function in G. sulfurreducens. Several genes encoding transcriptional regulators from the TetR and LuxR families were also found to be regulated by RpoN-dependent promoters. It is likely that RpoN directly controls transcription of some operons in G. sulfurreducens, while transcription of other operons is indirectly controlled by RpoN via FliA sigma factor and other transcriptional regulators. Other promoters with high scores were identified upstream of operons encoding components of regulation of nitrogen metabolism, signal transduction components, multiple -c-type cytochromes, members of ABC-type branched-chain transporter system, and ion transport proteins. The gene encoding the α subunit of DNA polymerase was also suggested to be controlled by an RpoN-regulated promoter. Analysis of target operons for predicted RpoN-regulated promoters and observed changes in their expression in the RpoN⁺ overexpressing strain allow for a better understanding of the interplay of various components of the RpoN-controlled cascade of transcriptional regulation and its role in Geobacter sensing of and response to environmental signals.