Outer membrane biogenesis and maintenance: atypical diderm Firmicutes do it differently

 Christophe Beloin

Abstract

The cell envelope is one of the most essential and ancient biological structures. While life has evolved a large diversity of envelope structures, one striking and major divide is evident in Bacteria, whose cells can be surrounded by either one membrane (Gram-positives or monoderms) or two (Gram-negatives or diderms). The outer membrane (OM) of diderm bacteria provides intrinsic resistance to many stresses, including antibiotics. While monumental progress has been made toward understanding the processes involved in the biogenesis and maintenance of the OM, there are still key questions and mechanistic details to elucidate. Moreover, outside a few model organisms, practically nothing is known on the systems involved in OM homeostasis in the vast majority of diderm bacteria, and how they originated and evolved.

We have focused on the Firmicutes (low GC Gram-positives) and have shown that they comprise at least three clades that have an OM with LPS (Negativicutes, Halanaerobiales, and Limnochordia). By carrying out phylogenomic analyses, we have proposed that the OM was already present in the ancestor of all Firmicutes and was lost repeatedly during the diversification of this phylum to give rise to the classical monoderm cell envelope. To study the mechanistic of the OM biogenesis and maintenance systems we have developed a novel model bacterium, Veillonella parvula, a member of the Negativicutes and a usual inhabitant of human microbiota. During my talk I would take two examples related to OM tethering and phospholipid transport to show that these diderm Firmicutes have peculiar ways to build and maintain their OM as compared to classically studied diderms. Our work not only help to better characterize essential functions related to the OM functioning in understudied bacteria but also inform on the evolution of these functions in bacteria.

Short Bio

I prepared my PhD in the laboratory of Structure and Expression of Bacterial Genome directed by Dr. Françoise Le Hégarat at the University Paris XI in Orsay where I studied histone-like proteins of the Gram positive bacterium Bacillus subtilis. I obtained my PhD in 1998. The same year I joined the laboratory of Prof. Charles J. Dorman at Trinity College Dublin as a European Post-doctoral fellow. During these three years my research was focused on the regulation of virulence gene expression in the pathogenic bacteria Shigella flexneri. In 2001, I came back to France on a postdoctoral position in the 5 years group recently created by Prof. Jean-Marc Ghigo at the Institut Pasteur Paris. In 2003, I was recruited at the Institut Pasteur as Assistant Professor (Chargé de Recherche). I'm leading a group of 4-5 people within Jean-Marc Ghigo’s team and have been promoted Associate Professor in 2014. Since 2011 I'm strongly involved in teaching at the Institut Pasteur and I have been appointed Co-director of the Institut Pasteur Microbiology Course in 2014. My work focuses on the identification and characterization of new bacterial adhesins with the development of different in vitro and in vivo models of bacterial biofilm infection to evaluate anti-biofilm strategies as well as to better understand the extreme recalcitrance of bacterial biofilms towards antibiotics. More recently, we developed a new model of anaerobic bacteria, Veillonella parvula, to study the origin and functioning of outer membrane essential elements.

 jeudi 23 mars 2023, 11h

Auditorium 442