UC San Diego

Sulfate-reducing bacterium such as Geobacter sulfurreducens have developed a set of responses that allow them to survive in environments with elevated temperatures. To obtain further knowledge of the protective mechanisms employed by G. sufurreducens and identify RpoH regulon in response to heat shock, we performed a Chromatin Immunopercipitation analysis followed by genome-wide expression profiling. We successfully identified RpoH regulon and confirmed it with gene expression experiment. The resulting genes, which had RpoH binding sites and were up-regulated with a fold change of at least two, were obtained. A total of 115 genes with known function, and 133 genes with unknown function were identified. As expected, molecular chaperons that refolded damaged proteins were induced. Proteases which promoted degradation to unrecoverable proteins were induced as well. The identified RpoH regulon was compared to E. coli proteome through orthology analysis. Those gene products that were not conservative with E. coli were functionally classified. Energy metabolic pathway was proposed, which utilized acetate and increased NADH production by activating glyoxylate synthesis. In addition, we found that Feo and Yfe iron transport systems were present in G. sulfurreducens and allowed Fe²⁺ import. The imported iron could be stored and /or utilized for cytochromes and Fe-S clusters production. The thioredoxin and thioredoxin reductase GSU3280 and GSU3281 genes were up-regulated and had RpoH binding sites. Our analysis proposed that thioredoxin acted as molecular chaperone for specific proteins in G. sulfurreducens. In addition, many other RpoH regulon characteristics were successfully recognized through this project.