Abstract
BackgroundTwo genotypically and microbiologically distinct strains of Mycobacterium avium subsp. paratuberculosis (MAP) exist - S and C MAP strains that primarily infect sheep and cattle, respectively. Concentration of iron in the cultivation medium has been suggested as one contributing factor for the observed microbiologic differences. We recently demonstrated that S strains have defective iron storage systems, leading us to propose that these strains might experience iron toxicity when excess iron is provided in the medium. To test this hypothesis, we carried out transcriptional and proteomic profiling of these MAP strains under iron-replete or -deplete conditions.ResultsWe first complemented M. smegmatisΔideR with IdeR of C MAP or that derived from S MAP and compared their transcription profiles using M. smegmatis mc2155 microarrays. In the presence of iron, sIdeR repressed expression of bfrA and MAP2073c, a ferritin domain containing protein suggesting that transcriptional control of iron storage may be defective in S strain. We next performed transcriptional and proteomic profiling of the two strain types of MAP under iron-deplete and -replete conditions. Under iron-replete conditions, C strain upregulated iron storage (BfrA), virulence associated (Esx-5 and antigen85 complex), and ribosomal proteins. In striking contrast, S strain downregulated these proteins under iron-replete conditions. iTRAQ (isobaric tag for relative and absolute quantitation) based protein quantitation resulted in the identification of four unannotated proteins. Two of these were upregulated by a C MAP strain in response to iron supplementation. The iron-sparing response to iron limitation was unique to the C strain as evidenced by repression of non-essential iron utilization enzymes (aconitase and succinate dehydrogenase) and upregulation of proteins of essential function (iron transport, [Fe-S] cluster biogenesis and cell division).ConclusionsTaken together, our study revealed that C and S strains of MAP utilize divergent metabolic pathways to accommodate in vitro iron stress. The knowledge of the metabolic pathways these divergent responses play a role in are important to 1) advance our ability to culture the two different strains of MAP efficiently, 2) aid in diagnosis and control of Johne's disease, and 3) advance our understanding of MAP virulence.
Highlights
Two genotypically and microbiologically distinct strains of Mycobacterium avium subsp. paratuberculosis (MAP) exist - S and C MAP strains that primarily infect sheep and cattle, respectively
We identified that 20 of the 24 previously predicted genes were differentially expressed in response to iron by MAP microarrays
Mycobactin synthesis, transport and fatty acid biosynthesis genes were repressed in the presence of iron by both cattle and sheep MAP strains (Additional file 1, Table S2)
Summary
Two genotypically and microbiologically distinct strains of Mycobacterium avium subsp. paratuberculosis (MAP) exist - S and C MAP strains that primarily infect sheep and cattle, respectively. We recently demonstrated that S strains have defective iron storage systems, leading us to propose that these strains might experience iron toxicity when excess iron is provided in the medium. To test this hypothesis, we carried out transcriptional and proteomic profiling of these MAP strains under iron-replete or -deplete conditions. We have demonstrated that IdeR of MAP in the presence of iron recognizes a consensus sequence on the promoter called “iron box” and regulates expression of genes involved in iron acquisition (mbt) and storage (bfrA). IdeR dependent repression of bfrA in the presence of iron suggests variations in iron storage mechanisms and/or iron requirements in cattle and sheep MAP strains
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