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Open Access Research article

Iron-sparing Response of Mycobacterium avium subsp. paratuberculosis is strain dependent

Harish K Janagama1, Senthilkumar16, John P Bannantine3, Abirami Kugadas1, Pratik Jagtap4, LeeAnn Higgins5, Bruce A Witthuhn5 and Srinand Sreevatsan12*

Author Affiliations

1 Department of Veterinary Population Medicine, University of Minnesota, Saint Paul MN, USA

2 Department of Veterinary and Biomedical Sciences, University of Minnesota, Saint Paul MN, USA

3 National Animal Disease Center, Agricultural Research Service, United States Department of Agriculture, Ames, IA, USA

4 Minnesota Supercomputing Institute for Advanced Computational Research, University of Minnesota, Minneapolis MN, USA

5 Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis MN, USA

6 Department of Animal Biotechnology, Madras Veterinary College, Chennai, India

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BMC Microbiology 2010, 10:268  doi:10.1186/1471-2180-10-268

Published: 22 October 2010

Abstract

Background

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. 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.

Results

We 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).

Conclusions

Taken 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.