Benn, Georgina Domville; (2021) Organisation and Disruption of the Outer Membrane of Escherichia coli. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

As disease-causing pathogens in the Enterobacteriaceae family, E. coli are part of the World Health Organisation’s critical list of antibiotic resistant bacteria, for which new therapies are urgently required1. They are Gram-negative bacteria, so have a complex envelope with an inner and outer membrane, separated by a peptidoglycan-containing periplasm. In particular the outer membrane provides a formidable protection against antibiotics2. As well as being clinically relevant, E. coli are extensively studied model organisms. But, despite their key role in the clinic and in research, major parts of their cell cycle and organisation are not fully understood, including the supramolecular architecture of the cell envelope, how the outer membrane is constricted as it divides and how our immune system targets the surface. In this thesis, atomic force microscopy is used to answer some of these questions by imaging the surface of live cells with nanometre resolution as they live, grow, divide, and die. The method is first optimised, to next allow the acquisition of data that reveals supramolecular organisations on the surface of dividing cells, answering questions on how the outer membrane is organised. A new potential role for a much-studied protein, OmpA, is also found, and evidence of phase separation in the outer membrane is revealed. Finally, the mechanism by which our immune system kills E. coli via the membrane attack complex is then studied, showing how complement-induced cell-death correlates with a mechanical destabilisation of the cell envelope.

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