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Emergent bistability by a growth-modulating positive feedback circuit

Nature Chemical Biology volume 5, pages 842848 (2009) | Download Citation

Abstract

Synthetic gene circuits are often engineered by considering the host cell as an invariable 'chassis'. Circuit activation, however, may modulate host physiology, which in turn can substantially impact circuit behavior. We illustrate this point by a simple circuit consisting of mutant T7 RNA polymerase (T7 RNAP*) that activates its own expression in the bacterium Escherichia coli. Although activation by the T7 RNAP* is noncooperative, the circuit caused bistable gene expression. This counterintuitive observation can be explained by growth retardation caused by circuit activation, which resulted in nonlinear dilution of T7 RNAP* in individual bacteria. Predictions made by models accounting for such effects were verified by further experimental measurements. Our results reveal a new mechanism of generating bistability and underscore the need to account for host physiology modulation when engineering gene circuits.

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    Isopropyl beta-D-1-thiogalactopyranoside

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    5a,6-Anhydrotetracycline

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Acknowledgements

We thank M. Salehi, G. Yao, J. Wong, H. Song, T.J. Lee, Q. Wang, J. Niemi, I. Molineux, M. Wall and W. Studier for discussions or comments; M. Cook for assistance with flow cytometry; W. Thompson, E. Soderblom and L. Dubois for assistance with mass spectrometry; M. Elowitz (California Institute of Technology), R. Weiss (Princeton University) and Y. Yokobayashi (University of California, Davis) for plasmids and bacterial strains; and T. Hwa for discussions and for sharing unpublished results. This work was partially supported by the US National Science Foundation (BES-0625213), the US National Institutes of Health (1P50GM081883), a DuPont Young Professorship (L.Y.), a David and Lucile Packard Fellowship (L.Y.) and a Medtronic Fellowship (C.T.).

Author information

Affiliations

  1. Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA.

    • Cheemeng Tan
    •  & Lingchong You
  2. Department of Biochemistry, Duke University, Durham, North Carolina, USA.

    • Philippe Marguet
  3. Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina, USA.

    • Lingchong You

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Contributions

C.T. conceived research, designed and performed both modeling and experimental analyses, interpreted results and wrote the manuscript. P.M. purified and analyzed T7 RNAP* and assisted in manuscript revisions. L.Y. conceived research, assisted in research design and data interpretation and wrote the manuscript. All authors approved the manuscript.

Corresponding author

Correspondence to Lingchong You.

Supplementary information

PDF files

  1. 1.

    Supplementary Text and Figures

    Supplementary Methods and Supplementary Results

Videos

  1. 1.

    Supplementary Video 1

    A time lapse movie corresponding to colony 1 in Fig. 1b, for 220 minutes of growth.

  2. 2.

    Supplementary Video 2

    A time lapse movie of another colony, for 335 minutes of growth under the same condition as in Supplementary Video 1.

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DOI

https://doi.org/10.1038/nchembio.218

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