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Summers Group

Microbial Genetics and Cell Signalling


Escherichia coli, bacterial plasmids, cell signalling, control of the bacterial cell cycle, indole, stress responses, bacterial cell factory

Research interests

Research in the Summers laboratory focussed originally on plasmids of E. coli and the mechanisms by which they ensure their stable inheritance. We demonstrated why plasmid dimer formation has a detrimental effect on plasmid maintenance and identified the mechanisms by which the plasmid counters this threat.

An unexpected discovery emerging from this work was that the multicopy plasmid ColE1, when damaged by dimerization, prevents the division of its bacterial host. This is achieved via a cell division checkpoint mediated by a 70 nt RNA, Rcd, that binds the enzyme tryptophanase, and stimulates indole production. Working in collaboration with Dr Ulrich Keyser at the Cavendish Laboratory, we demonstrated that indole blocks cell division by acting as a natural ionophore (a molecule that conducts ions through a lipid membrane in the absence of a protein pore). This represented an entirelynovel mechanism of cell cycle control. At the same time we found that indole inhibits plasmid replication by acting directly to inhibit DNA gyrase.

The elucidation of the mechanism of the Rcd checkpoint moved the focus of the group’s research towards bacterial signalling, and onto indole signalling in particular. Recently we have discovered an important role for indole signalling as E. coli makes the transition from exponential growth to stationary phase. The change of growth phase is accompanied by a brief (10-15 min) pulse of indole that transiently reaches >50 mM in the cells producing it.

Our current priority is to gain a better understanding of the mechanism of pulse signalling and to explore its role in bacterial responses to stress, including antibiotic action.

Applied research

The laboratory has been actively involved in the commercialization of discoveries arising from its basic research program. One major achievement has been the development of the Quiescent Cell Expression System (Q-Cells), a novel bacterial cell factory for the expression of metabolites in non-growing E. coli. Companies or individuals interested in using the Q-Cell system commercially or in their research should contact David Summers.

Key publications

  1. Gaimster, H. and Summers, D. (2015) Regulation of Indole Signalling during the Transition of E. coli from Exponential to Stationary Phase. PLoS One 10(9): e0136691
  2. Gaimster, H. and Summers, D. (2015) Plasmids in the driving seat: The regulatory RNA Rcd gives plasmid ColE1 control over division and growth of its E. coli host. Plasmid 78: 59-64
  3. Gaimster, H., Cama, J., Hernández-Ainsa, S., Keyser, U.F. and Summers D.K. The indole pulse: a new perspective on indole signalling in Escherichia coli. PLoS One. 2014 Apr 2; 9(4):e93168
  4. Chimerel, C., Field, C.M., Pinero-Fernandez, S., Keyser, U.F., and Summers, D.K. (2012). Indole prevents Escherichia coli cell division by modulating membrane potential. Biochimica et Biophysica Acta 1818, 1590-1594
  5. Field, C.M., and Summers, D.K. (2011). Multicopy plasmid stability: Revisiting the dimer catastrophe. J Theor Biol 291, 119-127
  6. Pinero-Fernandez, S., Chimerel, C., Keyser, U.F., and Summers, D.K. (2011). Indole transport across Escherichia coli membranes. Journal of Bacteriology 193: 1793-1798
  7. Summers, D. K. and Chant, E. (2010). Chemical induction in quiescence in bacteria. USPTO. United States Patent number 7,790,435
  8. Blaby, I.K. and Summers, D.K. (2009) The role of FIS in the Rcd checkpoint and stable maintenance of plasmid ColE1. Microbiology 155: 2676-2682

>> Full list of publications on PubMed

Page updated 21 September 2015

Contact details

Group leader : Dr David Summers

Department of Genetics,
University of Cambridge,
Downing Street,
Cambridge CB2 3EH,
United Kingdom


Tel.: +44 (0)1223 333991

Group members