Heat-shock sigma factor RpoH from Geobacter sulfurreducens

Abstract

Recent studies with Myxococcus xanthus have suggested that homologues of the Escherichia coli heat-shock sigma factor, RpoH, may not be involved in the heat-shock response in this d-proteobacterium. The genome of another d-proteobacterium, Geobacter sulfurreducens, which is considered to be a representative of the Fe(III)-reducing Geobacteraceae that predominate in a diversity of subsurface environments, contains an rpoH homologue. Characterization of the G. sulfurreducens rpoH homologue revealed that it was induced by a temperature shift from 30 6C to 42 6C and that an rpoH-deficient mutant was unable to grow at 42 6C. The predicted heat-shock genes, hrcA, grpE, dnaK, groES and htpG, were heat-shock inducible in an rpoH-dependent manner, and comparison of promoter regions of these genes identified the consensus sequences for the "10 and "35 promoter elements. In addition, DNA elements identical to the CIRCE consensus sequence were found in promoters of rpoH, hrcA and groES, suggesting that these genes are regulated by a homologue of the repressor HrcA, which is known to bind the CIRCE element. These results suggest that the G. sulfurreducens RpoH homologue is the heat-shock sigma factor and that heat-shock response in G. sulfurreducens is regulated positively by RpoH as well as negatively by the HrcA/CIRCE system. INTRODUCTIONThe Gram-negative d-proteobacterium Geobacter sulfurreducens is considered to be a representative of the Fe(III)-reducing Geobacteraceae that predominate in a diversity of subsurface environments where Fe(III) reduction is important . Geobacter species also play critical roles in bioremediation of groundwater contaminated with organic compounds or metals (Lloyd & Lovley, 2001;Lovley, 1997Lovley, , 2003Lovley & Coates, 1997, 2000 and in electricity production from waste organic matter (Bond et al., 2002;Bond & Lovley, 2003; Lovley, 2006a, b). However, the mechanisms they use to deal with the multiple stresses they encounter in these environments are poorly understood.Geobacter species face various environmental changes and growth conditions in the subsurface. Heat shock is a common stress to which all organisms adapt by inducing heat-shock proteins. Many heat-shock proteins are well conserved among organisms (Arrigo & Iandry, 1994;Lindquist & Craig, 1998). In bacteria, the expression of heat-shock genes is regulated in various fashions (Gross, 1996;Hecker et al., 1996;Narberhaus, 1999;Rosen & Ron, 2002;Schumann, 2000Schumann, , 2003Servant & Mazodier, 2001;Yura et al., 2000). The Gram-negative bacterium Escherichia coli uses two sigma factors, RpoH and RpoE, to activate transcription of heat-shock genes (Gross, 1996;Yura et al., 2000). The sigma factor, which is a subunit of RNA polymerase (RNAP), recognizes specific promoter elements and is essential for initiation of transcription. RpoHdependent transcription is also found in other Gramnegative bacteria (Gross, 1996;Yura et al., 2000;Rosen & Ron, 2002). The regulation of heat-shock gene expression in the Gram-positive bacterium Bacillus s...

Proteome of Geobacter sulfurreducens in the presence of U(VI)

“…RpoH is a sigma factor that regulates gene expression under heat shock (Ueki & Lovley, 2007) and a homologue of this gene was found to be upregulated when Caulobacter crescentus was exposed to U(VI) (Hu et al, 2005). Although the protein encoded by the rpoH homologue present in G. sulfurreducens (GSU0655) was not detected by our proteomic analysis, 33 proteins encoded by genes that contained RpoH-binding sites were expressed in higher abundance under U(VI) exposure (Table S20).…”

Insights into genes involved in electricity generation in Geobacter sulfurreducens via whole genome microarray analysis of the OmcF-deficient mutant

“…The OmcF-deficient mutant had increased transcript levels in genes related to heat shock response, such as the RpoH heat shock sigma factor [39], as well as several heat shock proteins and chaperones (GSU2408, GSU2390, GSU2406, and GSU0658) ( Table 5). The heat shock protein encoded by GSU2408 is in a family of lowmolecular-mass chaperone, α-crystallin-type proteins [40], that have been proposed to function in membrane stabilization [41] or to prevent irreversible aggregation of unfolding proteins [42].…”

Phylogenetic Classification of Diverse LysR-Type Transcriptional Regulators of a Model Prokaryote Geobacter sulfurreducens

“…Its genome sequence and reconstructed metabolism model are available (Mahadevan et al 2011;Methé et al 2003). Multiple genome, transcriptome, proteome, and metabolome experiments have been performed for this organism under different growth conditions and perturbations (Coppi et al 2001;Ding et al 2006Ding et al , 2008Mahadevan et al 2006;Methé et al 2005;Risso et al 2009;Segura et al 2008), and extensive analyses of its gene regulation and operon organization have been carried out (Juárez et al 2009;Leang et al 2009;Leang and Lovley 2005;Núñez et al 2006;Qiu et al 2010;Qu et al 2009;Rodionov et al 2004;Ueki and Lovley 2007, 2010a, 2010b. Genomes of multiple other species of Geobacteraceae have also been sequenced, annotated, and their growth and metabolism has been studied using experimental and modeling approaches (Aklujkar et al 2009(Aklujkar et al , 2010Butler et al 2009Butler et al , 2010Mahadevan et al 2011).…”