Interactions Between the Outer Membrane and the Peptidoglycan in Brucella abortus

PhD thesis defended by Pierre GODESSART (Prof. Xavier DE BOLLE) - 17/12/2021

Prof. Xavier DE BOLLE, UNamur, Research Unit in Biology of Microorganisms (URBM)

  • Prof. Waldemar VOLLMER (University of Newcastle, United Kingdom)
  • Dr. Axel CLOECKAERT (INRAE, France)
  • Prof. Jean-François COLLET (Université catholique de Louvain, Belgium)
  • Dr. Francesco RENZI (Université de Namur, Belgium)
  • Prof. Xavier DE BOLLE (Université de Namur, Belgium)

Gram-negative bacteria have an envelope made of three layers. The inner membrane (IM) and the outer membrane (OM) delimit the periplasmic space where the peptidoglycan (PG) is found. Together, these layers allow the bacterium to resist a variety of stresses, to transport molecules and to perform essential activities. Escherichia coli, the main Gram-negative model, has an abundant lipoprotein called Lpp, associated with the inner leaflet of the OM. Lpp is covalently bound to the PG allowing the anchorage of the OM. This tethering was shown important for envelope stability and stress sensing. However, the conservation of Lpp is mainly limited to Enterobacteriaceae. In this thesis, we aimed to study the interactions between the OM and the PG in the pathogen Brucella abortus. Overall, we characterized a novel anchorage system, in which the N-terminal extension of at least six OM β-barrels is covalently bound to PG. We identified the main enzyme catalysing this linkage, a putative enzyme able to remove these linkages, as well as a required and conserved N-terminal motif of the attached β-barrels. These data could be of major significance in the understanding of the envelope structure and resistance towards stresses in Rhizobiales.