Role of Rel_Gsuin Stress Response and Fe(III) Reduction inGeobacter sulfurreducens

Abstract

Geobacter species are key members of the microbial community in many subsurface environments in which dissimilatory metal reduction is an important process. The genome of Geobacter sulfurreducens contains a gene designated rel Gsu , which encodes a RelA homolog predicted to catalyze both the synthesis and the degradation of guanosine 3,5-bispyrophosphate (ppGpp), a regulatory molecule that signals slow growth in response to nutrient limitation in bacteria. To evaluate the physiological role of Rel Gsu in G. sulfurreducens, a rel Gsu mutant was constructed and characterized, and ppGpp levels were monitored under various conditions in both the wild-type and rel Gsu mutant strains. In the wild-type strain, ppGpp and ppGp were produced in response to acetate and nitrogen deprivation, whereas exposure to oxygen resulted in an accumulation of ppGpp alone. Neither ppGpp nor ppGp could be detected in the rel Gsu mutant. The rel Gsu mutant consistently grew to a higher cell density than the wild type in acetate-fumarate medium and was less tolerant of oxidative stress than the wild type. The capacity for Fe(III) reduction was substantially diminished in the mutant. Microarray and quantitative reverse transcription-PCR analyses indicated that during stationary-phase growth, protein synthesis genes were up-regulated in the rel Gsu mutant and genes involved in stress responses and electron transport, including several implicated in Fe(III) reduction, were down-regulated in the mutant. The results are consistent with a role for Rel Gsu in regulating growth, stress responses, and Fe(III) reduction in G. sulfurreducens under conditions likely to be prevalent in subsurface environments.

CcpA from Geobacter sulfurreducens Is a Basic Di-Heme Cytochrome c Peroxidase

“…9 Evidence for the involvement of CcpA in oxidative stress response was obtained previously from a mutant in rel GSU , a gene encoding a homolog of the stress response protein RelA/SpoT. 32 Here, various genes linked to oxidative stress were down-regulated and the rel GSU mutant also showed increased susceptibility to oxidative stress compared to the wild type. 32 GSU2813 was among the regulated genes and it does seem to form part of a complex answer of the bacterium to the presence of reactive oxygen species.…”

Genome-wide survey for PilR recognition sites of the metal-reducing prokaryote Geobacter sulfurreducens

“…An earlier study from our group (Leang and Lovley, 2005) also demonstrated that functional σ 70 family promoter elements within four protein-coding genes, GSU2735 (orfS), GSU2741 (orfR), GSU2732, and GSU2738 (orf2), regulate the expression of the omcB and the omcC operons of G. sulfurreducens. These genes are transcribed and translated, as demonstrated by multiple expression and proteomic experiments (Núñez et al, 2004;Leang and Lovley, 2005;DiDonato et al, 2006;Ding et al, 2006;Kim et al, 2008;Nevin et al, 2009). This suggests that the predicted PilR binding sites located within ORFs are of functional significance rather than false positive results.…”

The Stringent Response Controls Catalases in Pseudomonas aeruginosa and Is Required for Hydrogen Peroxide and Antibiotic Tolerance

“…Although the SR is a central stress response, only a few studies have examined its role in oxidative stress. For example, the relA mutant of Enterococcus faecalis is more susceptible to H 2 O 2 challenge than the wild type (14,15), while aerobic growth of the relA mutant of Geobacter sulfurreducens is impaired due to oxidative stress (56). Additionally, we and others have recently shown that SR inactivation in P. aeruginosa led to increased oxidant susceptibility (33,57).…”