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A fine balance between stress and success in synthetic circuit design

A new study has provided insights into how varying the number of synthetic circuits introduced into host cells influences their behaviour may provide a guide to improved synthetic circuit design.

Dr Baojun Wang of SynthSys and collaborators from the National University of Defense Technology, Changsha (China) and Imperial College London (UK) have interrogated these host-synthetic circuit interactions using RNA transcriptome analysis using an exemplar ‘AND gate’ circuit in Escherichia coli.

Synthetic biology approaches rely on introducing foreign (heterologous) gene networks into a host to program cells, with the assumption that expectation of the introduced synthetic network is orthogonal (i.e. not self) to the host background. However, synthetic circuits do still interfere with the host cell’s physiology by either posing a strain on host metabolism or inducing unintended interactions with host native gene pathways.

The team showed that the number of copies of synthetic circuits added had a more influential effect on host-cell interference than circuit composition per se: medium numbers of plasmids showed more prominent interference than low numbers. In contrast, the circuits have a stronger influence on host growth with an increasing metabolic load as the number of copies of the exemplar circuits increased. They noted that as they varied circuit copy number, from low to medium, the components behaved differently and, counterintuitively, attenuated output.

The study demonstrates the number of copies of the plasmid is a key factor that can dramatically affect the orthogonality, burden and functionality of the heterologous circuits in the host chassis. The results provide important guidance for future efforts to design orthogonal and robust gene circuits with minimal unwanted interaction and burden to their host.



Liu Q, Schumacher J, Wan X, Lou C and Wang B, “Orthogonality and burdens of heterologous AND gate gene circuits in E. coli”, ACS Synthetic Biology, (2017)  doi.10.1021/acssynbio.7b00328  (pdf

Published: December 14, 2017