Transcriptome and Physiological Responses to Hydrogen Peroxide of the Facultatively Phototrophic Bacterium Rhodobacter sphaeroides

Abstract

The transcriptome responses to hydrogen peroxide, H 2 O 2 , of the facultatively phototrophic bacterium Rhodobacter sphaeroides grown under semiaerobic conditions were investigated. At 7 min after the addition of 1 mM H 2 O 2 , the expression of approximately 9% of all genes (total, 394) was changed reliably by at least twofold. At 30 min, the number of genes (total, 88) and the magnitude of expression changes were much lower, indicating rapid recovery from stress. Two types of responses were observed: (i) an H 2 O 2 stress response per se and (ii) a shift to high-oxygen metabolism. The former response involved the upregulation of genes for H 2 O 2 detoxification, protein folding and proteolysis, DNA damage repair, iron transport and storage, iron-sulfur cluster repair, and the downregulation of genes for protein translation, motility, and cell wall and lipopolysaccharide synthesis. The shift to high-oxygen metabolism was evident from the differential regulation of genes for aerobic electron transport chain components and the downregulation of tetrapyrrole biosynthesis and photosystem genes. The abundance of photosynthetic complexes was decreased upon prolonged exposure of R. sphaeroides to H 2 O 2 , thus confirming the physiological significance of the transcriptome data. The regulatory pathways mediating the shift to high-oxygen metabolism were investigated. They involved the anaerobic activator FnrL and the antirepressor-repressor AppA-PpsR system. The transcription of FnrL-dependent genes was down at 7 min, apparently due to the transient inactivation by H 2 O 2 of the iron-sulfur cluster of FnrL. The transcription of the AppA-PpsR-dependent genes was down at 30 min, apparently due to the significant decrease in appA mRNA.In natural environments, microorganisms have to cope with oxidative stress caused by reactive oxygen species (ROS). In aerobically growing bacteria, the autooxidation of the respiratory chain components is believed to be one of the main sources of endogenous ROS (16,20,30); however, additional sources exist (48). ROS are also produced by exposure of aerobically grown cells to metals, redox-active chemicals, or radiation. To cope with damage inflicted by ROS, bacteria induce oxidative stress defense systems. These include superoxide dismutases, catalases, and peroxidases directly involved in ROS detoxification and repair mechanisms. The ROS-oxidized cysteine and methionine residues of proteins are repaired (reduced) by the thioredoxin, glutathion/glutaredoxin, and methionine sulfoxide reductase systems. DNA is protected from damage by specific ROS-induced DNA-binding proteins, while damaged DNA is repaired via the SOS response (1, 8, 52).Rhodobacter sphaeroides is a facultatively phototrophic bacterium belonging to the alpha division of the proteobacteria that can use various pathways for energy generation. At high O 2 tension, it uses aerobic respiration and lacks photosynthetic complexes. When O 2 tension drops, the expression of the photosystem (PS) genes increases, resulting in the produ...

Adaptation to Oxygen

“…These results not only underscore the importance of cbb 3 as an oxygen scavenger but also reinforce the relevant role of PpsR as a master regulator of photosystem and its requirement in the protection against photo-oxidative stress when cells are exposed to oxygen and light. This is in agreement with data obtained from R. sphaeroides transcriptome in responses to hydrogen peroxide where down-regulation of the photosynthesis gene is mediated under oxidative stress by the AppA-PpsR regulatory pathway (24).…”

Polymicrobial interactions stimulate resistance to host innate immunity through metabolite perception

“…1B). This is in stark contrast to similar studies with other bacteria, in which 140-520 genes were differentially expressed on H 2 O 2 exposure (18)(19)(20)(21)(22)(23) (18,20,23). More surprising was the H 2 O 2 -mediated induction of apiA.…”

“…Not surprisingly, A. actinomycetemcomitans displayed enhanced production of the H 2 O 2 -consuming enzyme catalase during coculture. This response has been observed previously in several bacterial species and serves to enhance resistance to H 2 O 2 (18)(19)(20)(21)(22)(23)29). More intriguing was the finding that A. actinomycetemcomitans also induces the outer membrane protein ApiA during coculture.…”

“…4 A and B). Although it is clear that katA is a critical component of H 2 O 2 resistance in numerous bacteria (18)(19)(20)(21)(22)(23)29), it was not known if the decrease in serum resistance was attributable to decreased levels of apiA. To test this possibility, apiA was constitutively expressed in the oxyR Ϫ mutant (27).…”

The phrA gene of Rhodobacter sphaeroides encodes a photolyase and is regulated by singlet oxygen and peroxide in a σ E-dependent manner

“…In contrast to this previous study, we found a significant upregulation of phrA (Fig. 4) and a similar upregulation in rpoE expression (not shown) due to H 2 O 2 stress using real-time RT-PCR and DNA microarray analysis (Zeller et al, 2005).…”