Maintaining cell wall integrity in Gram-Negative Bacteria

BBSRC: Christopher Graham: BB/M01116X/1

The development of resistance to antibiotics by pathogenic bacteria already undermines modern and future healthcare and has been acknowledged as a worldwide issue with an impact as important as climate change. We are in initial stages of a post-antibiotics era, akin to the pre-19th century world in terms of the danger from infections. Or particular concern in this respect are Gram-negative bacteria since their outer membrane presents a particular barrier to entry of existing and future antibiotics.

The pharmaceutical industry has reduced in its capacity and commitment to funding antibiotic discovery in recent years due to complex economic issues, however, a large proportion of successful antibiotics have been those based on targeting the cell walls of bacteria generally. Both Gram-negative bacteria and Gram-positive bacteria have an inner membrane and cell wall peptidoglycan polymer however a third outer layer known as the outer membrane is unique to Gram-negatives. This outer membrane in Gram-negative bacteria's greatest defence against most antibiotics since it provides a significant barrier to their entry as well as having an important biological role in Gram-negative bacterial physiology. Our hypothesis is that the process of cell wall peptidoglycan and outer membrane biogenesis must be linked and if we understood this process then it may lead to the use of combinatorial antibiotics strategies that affect both systems synergistically. This would allow us to truly break down Gram-negative bacterial pathogens, disrupting the outer-membrane, therefore, allowing peptidoglycan affecting drugs to pass. We have preliminary data that shows disruption of the peptidoglycan synthesis system actually causes outer membrane destabilisation and increased bacterial susceptibility, and hypothesise the outer membrane and peptidoglycan layers are created simultaneously and locally through complex interactions.

We have established a collaboration with Professor Lori Burrows at McMaster University in Canada who has the specialist genetic tools and facilities to enable us to explore this hypothesis in P. aeuginosa, one of the most important Gram-Negative pathogens. The University of Warwick does not currently have the facilities or expertise to do this but our collaboration with Canada will allow this knowledge to be gained and facilitate a parallel study in E.coli in the future. We aim in this study, to show the co-ordination of the proteins responsible for outer membrane and peptidoglycan synthesis by making bacterial strains in which individual pairs of proteins are specially fluorescently tagged allowing us to use appropriate microscopy to visualise their co-localisation. This will establish at a molecular level how these processes are linked and what proteins may be involved. Previously both outer membrane peptidoglycan biogenesis has been studied as separate events but knowledge gained in this collaboration could be of fundamental biological importance as well as the basis upon which future antimicrobial strategies that target the two processes in parallel are based. The study in Canada will be undertaken by a highly talented UK PhD student who will learn new skills, be exposed to an entirely different research environment and thus gain enormously from this international training opportunity.