Whole-Genome Expression Profiling of Bradyrhizobium japonicum in Response to Hydrogen Peroxide

Abstract

Bradyrhizobium japonicum, a nitrogen-fixing bacterium in soil, establishes a symbiotic relationship with the leguminous soybean plant. Despite a mutualistic association between the two partners, the host plant produces an oxidative burst to protect itself from the invasion of rhizobial cells. We investigated the effects of H(2)O(2)-mediated oxidative stress on B. japonicum gene expression in both prolonged exposure (PE) and fulminant shock (FS) conditions. In total, 439 and 650 genes were differentially expressed for the PE and FS conditions, respectively, at a twofold cut-off with q < 0.05. A number of genes within the transport and binding proteins category were upregulated during PE and a majority of those genes are involved in ABC transporter systems. Many genes encoding ? factors, global stress response proteins, the FixK(2) transcription factor, and its regulatory targets were found to be upregulated in the FS condition. Surprisingly, catalase and peroxidase genes which are typically expressed in other bacteria under oxidative stress were not differentially expressed in either condition. The isocitrate lyase gene (aceA) was induced by fulminant H(2)O(2) shock, as was evident at both the transcriptional and translational levels. Interestingly, there was no significant effect of H(2)O(2) on exopolysaccharide production at the given experimental conditions.

Antimicrobial Nodule-Specific Cysteine-Rich Peptides Induce Membrane Depolarization-Associated Changes in the Transcriptome of Sinorhizobium meliloti

“…Similarly to NCR peptides in S. meliloti, the human AMP, the cathelicidin-derived linear LL-37 peptide (21), downregulated the S. pneumoniae genes coding for RNA polymerases and helicases, ribosomal subunits, and translation initiation and elongation factors (22). The effects of AMPs and AMP-like peptides on gene expression are similar to those caused by exposure to hydrogen peroxide, as was demonstrated in Bradyrhizobium japonicum by both fulminant shock and prolonged exposure to this chemical (23). The upregulated genes also show some similarities.…”

Reactive Oxygen Species-Inducible ECF σ Factors of Bradyrhizobium japonicum

“…In recent studies, effects of H 2 O 2 and paraquat exposure on transcription in oxically grown B. japonicum cells were described [49], [50]. A comparison of that study with our own results revealed that genes induced by H 2 O 2 in both oxic and micro-oxic cells comprise those encoding hydroperoxide resistance proteins (bll4012, bll0735), putative epoxide hydrolase 1 (bll3418), a putative glutathione S-transferase (bll7849), and the ECF σ factors mentioned above (e cfQ , ecfF ).…”

DNA Microarray-Based Identification of Genes Regulated by NtrC in Bradyrhizobium japonicum

“…B. japonicum strains were cultured in 20 ml of MMB glutamate or MMB glutamate plus ammonium to an OD 600 of 0.4 to 0.6. Cells were harvested and RNA was extracted as described previously (26)(27)(28). Synthesis of cDNA and quantitative reverse transcription-PCR (qRT-PCR) was performed using 3 g of total RNA as described previously (26)(27)(28).…”

“…Cells were harvested and RNA was extracted as described previously (26)(27)(28). Synthesis of cDNA and quantitative reverse transcription-PCR (qRT-PCR) was performed using 3 g of total RNA as described previously (26)(27)(28). Data for three independent biological replicates were generated and normalized to the expression of the bll7457 gene, encoding the histidyl-tRNA synthetase HisS.…”