Unknown,Transcriptomics,Genomics,Proteomics

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A unique iron homeostasis regulatory circuit with reciprocal roles in Candida albicans commensalism and pathogenesis [ChIP_chip]

ABSTRACT: The mammalian gastrointestinal tract and the bloodstream are highly disparate biological niches, and yet certain commensal-pathogenic microorganisms are able to thrive in both environments. Here, we report the evolution of a unique transcription circuit in the yeast, Candida albicans, which determines its fitness in both host niches. Our comprehensive analysis of the DNA-binding proteins that regulate iron uptake by this organism suggests the evolutionary intercalation of a transcriptional activator called Sef1 between two broadly conserved transcriptional repressors, Sfu1 and Hap43. The Sef1 activator of iron uptake genes promotes virulence in a mouse model of bloodstream infection, whereas the Sfu1 repressor is dispensable for virulence but promotes gastrointestinal commensalism. We propose that the ability to alternate between genetic programs conferring resistance to iron depletion in the bloodstream versus iron toxicity in the gut may be a fundamental attribute of gastrointestinal commensal-pathogens. ChIP analyses to profile genome-wide of distribution of Sef1, Sfu1 and Hap43 in response to various iron availability. 12 independent ChIP experiments were performed on 6 biological replicates of the untagged control and 2 biological replicates each of Sef1-Myc, Sfu1-Myc, and Hap43-Myc.

ORGANISM(S): Candida albicans

SUBMITTER: Changbin Chen

PROVIDER: E-GEOD-30591 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Because iron toxicity and deficiency are equally life threatening, maintaining intracellular iron levels within a narrow optimal range is critical for nearly all known organisms. However, regulatory mechanisms that establish homeostasis are not well understood in organisms that dwell in environments at the extremes of pH, temperature, and salinity. Under conditions of limited iron, the extremophile Halobacterium salinarum, a salt-loving archaeon, mounts a specific response to scavenge iron for growth. We have identified and characterized the role of two transcription factors (TFs), Idr1 and Idr2, in regulating this important response. An integrated systems analysis of TF knockout gene expression profiles and genome-wide binding locations in the presence and absence of iron has revealed that these TFs operate collaboratively to maintain iron homeostasis. In the presence of iron, Idr1 and Idr2 bind near each other at 24 loci in the genome, where they are both required to repress some genes. In contrast, Idr1 and Idr2 are both necessary to activate other genes in a putative a feed forward loop. Even at loci bound independently, the two TFs target different genes with similar functions in iron homeostasis. We discuss conserved and unique features of the Idr1-Idr2 system in the context of similar systems in organisms from other domains of life. Data in this GEO archive are linked to the publication: Schmid AK, Pan M, Sharma K, Baliga NS.2011. Two transcription factors are necessary for iron homeostasis in a salt-dwelling archaeon.Nucleic Acids Res.39(7):2519-33. The Δura3 parent, Δidr2 and Δidr1, and Δ idr1Δidr2 mutant strains were grown to mid-logarithmic phase (OD600 ~0.4 – 0.8) in CDM with all trace metals except iron. Cultures were split in half and FeSO4 was added to one half, while the other was continued under iron limitation. 8-mL samples were collected from each culture every 20 minutes for 60 minutes (see also experimental design, Supplementary Figure 1, Schmid et al., 2011). RNA from two biological replicate time courses were prepared, averages of these replicates are reported in the published study, whereas data from each replicate are reported here. The zero time point was harvested immediately before the addition of iron. Each Sample is based on two arrrays (one with dye-swap).

Project description:In the alpha subclass of proteobacteria iron homeostasis is controlled by diverse iron responsive regulators. Caulobacter crescentus, an important freshwater Î±-proteobacterium, uses the ferric uptake repressor (Fur) for such purpose. However, the impact of the iron availability on the C. crescentus transcriptome and an overall perspective of the regulatory networks involved remain unknown. In this work we report the identification of iron-responsive and Fur-regulated genes in C. crescentus using microarray-based global transcriptional analyses. We identify 46 genes that were strongly upregulated both by mutation of fur and by iron limitation condition. Among them, there are genes involved in iron uptake (four TonB dependent receptor gene clusters, feoAB), riboflavin biosynthesis and some genes encoding hypothetical proteins. Most of these genes are associated with Fur binding sites, implicating them as direct targets of Fur-mediated repression. These data were validated by Î²-galactosidase and EMSA assays for two operons encoding putative transporters. The role of Fur as a positive regulator is also evident, given that 50 genes were downregulated both by mutation of fur and under low-iron condition. As expected, this group includes many genes involved in energy metabolism, mostly iron-using enzymes. Surprisingly, are also included in this group many genes encoding TonB dependent receptors and the genes fixK, fixT and ftrB encoding an oxygen signaling network required for growth during hypoxia. Bioinformatics analyses performed in the promoters of these genes suggest that positive regulation by Fur is mainly indirect. In addition to the Fur modulon, iron limitation altered expression of more 103 genes, including upregulation of genes involved in Fe-S cluster assembly, oxidative stress and heat shock response, as well as downregulation of genes implicated in amino acid metabolism, chemotaxis and motility. Altogether, our results showed that adaptation of C. crescentus to iron limitation involves increasing the transcription of iron-acquisition systems and decreasing the production of iron-using proteins as a general strategy Two experimental procedures, each of them performed in two replicates. A total of four independent biological samples were used

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A unique iron homeostasis regulatory circuit with reciprocal roles in Candida albicans commensalism and pathogenesis [ChIP_chip]

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