Molecular Imaging and Biology

, Volume 20, Issue 1, pp 65–73 | Cite as

Characterization of Magneto-Endosymbionts as MRI Cell Labeling and Tracking Agents

  • Kimberly D. Brewer
  • Ryan Spitler
  • Kayla R. Lee
  • Andrea C. Chan
  • Joyce C. Barrozo
  • Abdul Wakeel
  • Chandler S. Foote
  • Steven Machtaler
  • James Rioux
  • Juergen K. Willmann
  • Papia Chakraborty
  • Bradley W. Rice
  • Christopher H. Contag
  • Caleb B. BellIII
  • Brian K. RuttEmail author
Research Article



Magneto-endosymbionts (MEs) show promise as living magnetic resonance imaging (MRI) contrast agents for in vivo cell tracking. Here we characterize the biomedical imaging properties of ME contrast agents, in vitro and in vivo.


By adapting and engineering magnetotactic bacteria to the intracellular niche, we are creating magneto-endosymbionts (MEs) that offer advantages relative to passive iron-based contrast agents (superparamagnetic iron oxides, SPIOs) for cell tracking. This work presents a biomedical imaging characterization of MEs including: MRI transverse relaxivity (r 2) for MEs and ME-labeled cells (compared to a commercially available iron oxide nanoparticle); microscopic validation of labeling efficiency and subcellular locations; and in vivo imaging of a MDA-MB-231BR (231BR) human breast cancer cells in a mouse brain.


At 7T, r 2 relaxivity of bare MEs was higher (250 s−1 mM−1) than that of conventional SPIO (178 s−1 mM−1). Optimized in vitro loading of MEs into 231BR cells yielded 1–4 pg iron/cell (compared to 5–10 pg iron/cell for conventional SPIO). r 2 relaxivity dropped by a factor of ~3 upon loading into cells, and was on the same order of magnitude for ME-loaded cells compared to SPIO-loaded cells. In vivo, ME-labeled cells exhibited strong MR contrast, allowing as few as 100 cells to be detected in mice using an optimized 3D SPGR gradient-echo sequence.


Our results demonstrate the potential of magneto-endosymbionts as living MR contrast agents. They have r 2 relaxivity values comparable to traditional iron oxide nanoparticle contrast agents, and provide strong MR contrast when loaded into cells and implanted in tissue.

Key words

Magnetic resonance imaging (MRI) Magnetotactic bacteria Magnetite Labeled cells Iron Cell tracking 



The authors would like to acknowledge technical assistance from Adam Shuhendler, Marjan Rafat, Edward Graves, and Rehan Ali, and the support from the following funding sources: NIH SBIR Phase I 1R43TR001202-01, CIRM RT2-02018, and NIH T32-CA-009695.

Compliance with Ethical Standards

Conflict of Interest

Ryan Spitler was a consultant for Bell Biosystems Inc. Kayla R. Lee, Andrea C. Chan, Joyce C. Barrozo, Abdul Wakeel, Chandler S. Foote, Papia Chakraborty and Bradley W. Rice were all employed by Bell Biosystems during this work. Christopher H. Contag serves on the scientific advisory board of Bell Biosystems. Caleb B. Bell III is the CEO of Bell Biosystems.


  1. 1.
    Li L, Jiang W, Luo K et al (2013) Superparamagnetic iron oxide nanoparticles as MRI contrast agents for non-invasive stem cell labeling and tracking. Theranostics 3:595–615CrossRefPubMedPubMedCentralGoogle Scholar
  2. 2.
    Schlorf T, Meincke M, Kossel E et al (2010) Biological properties of iron oxide nanoparticles for cellular and molecular magnetic resonance imaging. Int J Mol Sci 12:12–23CrossRefPubMedPubMedCentralGoogle Scholar
  3. 3.
    Bulte JW (2009) In vivo MRI cell tracking: clinical studies. Am J Roentgenol 193:314–325CrossRefGoogle Scholar
  4. 4.
    Foster-Gareau P, Heyn C, Alejski A, Rutt BK (2003) Imaging single mammalian cells with a 1.5 T clinical MRI scanner. Magn Reson Med 49:968–971CrossRefPubMedGoogle Scholar
  5. 5.
    Heyn C, Ronald JA, Ramadan SS et al (2006) In vivo MRI of cancer cell fate at the single-cell level in a mouse model of breast cancer metastasis to the brain. Magn Reson Med 56:1001–1010CrossRefPubMedGoogle Scholar
  6. 6.
    Ahrens ET, Bulte JW (2013) Tracking immune cells in vivo using magnetic resonance imaging. Nat Rev Immunol 13:755–763CrossRefPubMedGoogle Scholar
  7. 7.
    Roohi F, Lohrke J, Ide A et al (2012) Studying the effect of particle size and coating type on the blood kinetics of superparamagnetic iron oxide nanoparticles. Int J Nanomedicine 7:4447–4458PubMedPubMedCentralGoogle Scholar
  8. 8.
    Bernau K, Lewis CM, Petelinsek AM et al (2016) In vivo tracking of human neural progenitor cells in the rat brain using magnetic resonance imaging is not enhanced by ferritin expression. Cell Transplant 25:575–592CrossRefPubMedGoogle Scholar
  9. 9.
    Cevenini L, Calabretta MM, Calabria D et al (2015) Luciferase genes as reporter reactions: how to use them in molecular biology? Adv Biochem Eng Biotechnol 154:3–17Google Scholar
  10. 10.
    Youn H, Chung JK (2013) Reporter gene imaging. Am J Roentgenol 201:W206–W214CrossRefGoogle Scholar
  11. 11.
    Naumova AV, Modo M, Moore A et al (2014) Clinical imaging in regenerative medicine. Nat Biotechnol 32:804–818CrossRefPubMedPubMedCentralGoogle Scholar
  12. 12.
    Pereira SM, Moss D, Williams SR et al (2015) Overexpression of the MRI reporter genes ferritin and transferrin receptor affect iron homeostasis and produce limited contrast in mesenchymal stem cells. Int J Mol Sci 16:15481–15496CrossRefPubMedPubMedCentralGoogle Scholar
  13. 13.
    Vandsburger MH, Radoul M, Cohen B, Neeman M (2013) MRI reporter genes: applications for imaging of cell survival, proliferation, migration and differentiation. NMR Biomed 26:872–884CrossRefPubMedGoogle Scholar
  14. 14.
    Vande Velde G, Himmelreich U, Neeman M (2013) Reporter gene approaches for mapping cell fate decisions by MRI: promises and pitfalls. Contrast Media Mol Imaging 8:424–431CrossRefPubMedGoogle Scholar
  15. 15.
    Patrick PS, Rodrigues TB, Kettunen MI et al (2016) Development of Timd2 as a reporter gene for MRI. Magn Reson Med 75:1697–1707CrossRefPubMedGoogle Scholar
  16. 16.
    Naumova AV, Yarnykh VL, Balu N et al (2012) Quantification of MRI signal of transgenic grafts overexpressing ferritin in murine myocardial infarcts. NMR Biomed 25:1187–1195CrossRefPubMedPubMedCentralGoogle Scholar
  17. 17.
    Naumova AV, Reinecke H, Yarnykh V et al (2010) Ferritin overexpression for noninvasive magnetic resonance imaging-based tracking of stem cells transplanted into the heart. Mol Imaging 9:201–210PubMedPubMedCentralGoogle Scholar
  18. 18.
    He X, Cai J, Liu B et al (2015) Cellular magnetic resonance imaging contrast generated by the ferritin heavy chain genetic reporter under the control of a Tet-On switch. Stem Cell Res Ther 6:207CrossRefPubMedPubMedCentralGoogle Scholar
  19. 19.
    Pereira SM, Herrmann A, Moss D et al (2016) Evaluating the effectiveness of transferrin receptor-1 (TfR1) as a magnetic resonance reporter gene. Contrast Media Mol Imaging 11:236–244CrossRefPubMedPubMedCentralGoogle Scholar
  20. 20.
    Zhang XY, Robledo BN, Harris SS, Hu XP (2014) A bacterial gene, mms6, as a new reporter gene for magnetic resonance imaging of mammalian cells. Mol Imaging 13:2–12Google Scholar
  21. 21.
    Goldhawk DE, Gelman N, Sengupta A, Prato FS (2015) The interface between iron metabolism and gene-based iron contrast for MRI. Magn Reson Insights 8(Suppl 1):9–14CrossRefPubMedPubMedCentralGoogle Scholar
  22. 22.
    Zurkiya O, Chan AW, Hu X (2008) MagA is sufficient for producing magnetic nanoparticles in mammalian cells, making it an MRI reporter. Magn Reson Med 59:1225–1231CrossRefPubMedPubMedCentralGoogle Scholar
  23. 23.
    Yan L, Zhang S, Chen P et al (2012) Magnetotactic bacteria, magnetosomes and their application. Microbiol Res 167:507–519CrossRefPubMedGoogle Scholar
  24. 24.
    Mahmoudi M, Tachibana A, Goldstone AB et al (2016) Novel MRI contrast agent from magnetotactic bacteria enables in vivo tracking of iPSC-derived cardiomyocytes. Sci Rep 6:26960CrossRefPubMedPubMedCentralGoogle Scholar
  25. 25.
    Agapakis CM, Niederholtmeyer H, Noche RR et al (2011) Towards a synthetic chloroplast. PLoS One 6(4):e18877CrossRefPubMedPubMedCentralGoogle Scholar
  26. 26.
    Amsalem Y, Mardor Y, Feinberg MS et al (2007) Iron-oxide labeling and outcome of transplanted mesenchymal stem cells in the infarcted myocardium. Circulation 116(Suppl):I38–I45PubMedGoogle Scholar
  27. 27.
    Berman SC, Galpoththawela C, Gilad AA et al (2011) Long-term MR cell tracking of neural stem cells grafted in immunocompetent versus immunodeficient mice reveals distinct differences in contrast between live and dead cells. Magn Reson Med 65:564–574CrossRefPubMedGoogle Scholar
  28. 28.
    Srivastava AK, Bulte JW (2014) Seeing stem cells at work in vivo. Stem Cell Rev 10:127–144CrossRefPubMedPubMedCentralGoogle Scholar
  29. 29.
    Guenoun J, Ruggiero A, Doeswijk G et al (2013) In vivo quantitative assessment of cell viability of gadolinium or iron-labeled cells using MRI and bioluminescence imaging. Contrast Media Mol Imaging 8:165–174CrossRefPubMedGoogle Scholar
  30. 30.
    Nguyen PK, Riegler J, Wu JC (2014) Stem cell imaging: from bench to bedside. Cell Stem Cell 14:431–444CrossRefPubMedPubMedCentralGoogle Scholar
  31. 31.
    Benoit MR, Mayer D, Barak Y et al (2009) Visualizing implanted tumors in mice with magnetic resonance imaging using magnetotactic bacteria. Clin Cancer Res 15:5170–5177CrossRefPubMedPubMedCentralGoogle Scholar
  32. 32.
    Lee KR, Wakeel A, Chakraborty P et al (2017) Cell labeling with magneto-endosymbionts and the dissection of the subcellular location, fate and host cell interactions. Molecular Imaging and Biology. doi: 10.1007/s11307-017-1094-6
  33. 33.
    Rosset A, Spadola L, Ratib O (2004) OsiriX: an open-source software for navigating in multidimensional DICOM images. J Digit Imaging 17:205–216CrossRefPubMedPubMedCentralGoogle Scholar
  34. 34.
    Studholme C (2016) RView Software, Version #9.043BGoogle Scholar
  35. 35.
    Khurana A, Nejadnik H, Chapelin F et al (2013) Ferumoxytol: a new, clinically applicable label for stem-cell tracking in arthritic joints with MRI. Nanomedicine (Lond) 8:1969–1983CrossRefGoogle Scholar
  36. 36.
    Shen WB, Plachez C, Chan A et al (2013) Human neural progenitor cells retain viability, phenotype, proliferation, and lineage differentiation when labeled with a novel iron oxide nanoparticle, Molday ION Rhodamine B. Int J Nanomedicine 8:4593–4600PubMedPubMedCentralGoogle Scholar
  37. 37.
    Meriaux S, Boucher M, Marty B et al (2015) Magnetosomes, biogenic magnetic nanomaterials for brain molecular imaging with 17.2 T MRI scanner. Adv Healthc Mater 4:1076–1083CrossRefPubMedGoogle Scholar
  38. 38.
    Taylor A, Herrmann A, Moss D et al (2014) Assessing the efficacy of nano- and micro-sized magnetic particles as contrast agents for MRI cell tracking. PLoS One 9:e100259CrossRefPubMedPubMedCentralGoogle Scholar
  39. 39.
    Rozenman Y, Zou XM, Kantor HL (1990) Cardiovascular MR imaging with iron oxide particles: utility of a superparamagnetic contrast agent and the role of diffusion in signal loss. Radiology 175:655–659CrossRefPubMedGoogle Scholar
  40. 40.
    Ghugre NR, Coates TD, Nelson MD, Wood JC (2005) Mechanisms of tissue-iron relaxivity: nuclear magnetic resonance studies of human liver biopsy specimens. Magn Reson Med 54:1185–1193CrossRefPubMedPubMedCentralGoogle Scholar
  41. 41.
    Lefevre CT, Bazylinski DA (2013) Ecology, diversity, and evolution of magnetotactic bacteria. Microbiol Mol Biol Rev 77:497–526CrossRefPubMedPubMedCentralGoogle Scholar
  42. 42.
    Yablonskiy DA, Haacke EM (1994) Theory of NMR signal behavior in magnetically inhomogeneous tissues: the static dephasing regime. Magn Reson Med 32:749–763CrossRefPubMedGoogle Scholar
  43. 43.
    Bowen CV, Zhang X, Saab G et al (2002) Application of the static dephasing regime theory to superparamagnetic iron-oxide loaded cells. Magn Reson Med 48:52–61CrossRefPubMedGoogle Scholar

Copyright information

© World Molecular Imaging Society 2017

Authors and Affiliations

  • Kimberly D. Brewer
    • 1
    • 2
  • Ryan Spitler
    • 2
  • Kayla R. Lee
    • 3
  • Andrea C. Chan
    • 3
  • Joyce C. Barrozo
    • 3
  • Abdul Wakeel
    • 3
  • Chandler S. Foote
    • 3
  • Steven Machtaler
    • 2
  • James Rioux
    • 1
    • 2
  • Juergen K. Willmann
    • 2
  • Papia Chakraborty
    • 3
  • Bradley W. Rice
    • 3
  • Christopher H. Contag
    • 2
  • Caleb B. BellIII
    • 3
  • Brian K. Rutt
    • 2
    • 4
    Email author
  1. 1.Biomedical Translational Imaging Centre (BIOTIC)HalifaxCanada
  2. 2.Radiology Department and Molecular Imaging Program (MIPS)Stanford UniversityStanfordUSA
  3. 3.Bell BiosystemsSan FranciscoUSA
  4. 4.Richard M. Lucas Center for ImagingStanford University School of MedicineStanfordUSA

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