Role of the Irr Protein in the Regulation of Iron Metabolism in Rhodobacter sphaeroides

Abstract

In Rhizobia the Irr protein is an important regulator for iron-dependent gene expression. We studied the role of the Irr homolog RSP_3179 in the photosynthetic alpha-proteobacterium Rhodobacter sphaeroides. While Irr had little effect on growth under iron-limiting or non-limiting conditions its deletion resulted in increased resistance to hydrogen peroxide and singlet oxygen. This correlates with an elevated expression of katE for catalase in the Irr mutant compared to the wild type under non-stress conditions. Transcriptome studies revealed that Irr affects the expression of genes for iron metabolism, but also has some influence on genes involved in stress response, citric acid cycle, oxidative phosphorylation, transport, and photosynthesis. Most genes showed higher expression levels in the wild type than in the mutant under normal growth conditions indicating an activator function of Irr. Irr was however not required to activate genes of the iron metabolism in response to iron limitation, which showed even stronger induction in the absence of Irr. This was also true for genes mbfA and ccpA, which were verified as direct targets for Irr. Our results suggest that in R. sphaeroides Irr diminishes the strong induction of genes for iron metabolism under iron starvation.

A Cluster of Four Homologous Small RNAs Modulates C 1 Metabolism and the Pyruvate Dehydrogenase Complex in Rhodobacter sphaeroides under Various Stress Conditions

“…For Northern blot analysis, total RNA was isolated by the hot-phenol method (27) and quantified photometrically at 260 nm with a NanoDrop 1000 UV/Vis spectrophotometer (PeqLab). For transcriptome analysis, total RNA was isolated as described previously (28). In short, RNA was extracted by the hot-phenol method and contaminating DNA was removed by DNase I (Invitrogen) treatment.…”

“…Two individual microarrays (biological replicates), each containing a pool of three independent experiments for each strain, were applied as follows. Two micrograms of pooled total RNA from R. sphaeroides strains 2.4.1(pRK415) and 2.4.1(pRCcsR1-4) was labeled with Cy5 and Cy3, respectively, with the ULS Fluorescent Labeling kit for Agilent arrays (Kreatech) and competitively hybridized to Custom Gene Expression Microarrays from Agilent Technologies (8x15K; ID 027061) designed for wild-type R. sphaeroides 2.4.1 (28). Sample fragmentation, hybridization, and data scanning were performed in accordance with the specifications given by Agilent.…”

Iron Response Regulator Protein IrrB in Magnetospirillum gryphiswaldense MSR-1 Helps Control the Iron/Oxygen Balance, Oxidative Stress Tolerance, and Magnetosome Formation

“…Scanning of the entire MSR-1 genome did not reveal a gene promoter with an ICE box, suggesting that Irr proteins may recognize different ICE motifs in MSR-1. Comparison with Irr-regulated gene sequences in nonmagnetotactic bacteria (24,25) revealed eight homologous genes in the MSR-1 genome. mRNAs transcribed from these genes were quantified by RT-qPCR.…”

Iron homeostasis in the Rhodobacter genus

“…Transcription of Bfr encoded by orf 1546, along with its associated ferredoxin appears to be controlled by iron availability as their mRNA levels increase when iron is depleted. The transcription factor Irr is implicated in this control (Peuser et al, 2012). The other Bfr (orf 3342), which lacks a linked ferredoxin, is almost insensitive to iron levels and shows a weak Irr regulation profile (Peuser et al, 2012).…”

“…The transcription factor Irr is implicated in this control (Peuser et al, 2012). The other Bfr (orf 3342), which lacks a linked ferredoxin, is almost insensitive to iron levels and shows a weak Irr regulation profile (Peuser et al, 2012). Finally, the Ftn-like MbfA displays weak iron control but a strong Irr-dependence.…”