genetics of bacterial envelopes

The perception of their environment by bacteria is vital to adapt to variations, from harmless to lethal, of this environment. In particular, during infection, pathogenic bacteria must recognize the host (their new environment) but above all protect themselves against the violent defense of this host to invasion. The two-component systems (TCS) are the main systems for detecting variations in bacteria and are like the sonar systems of submarines: their eyes and ears.

TCSs consist of a transmembrane sensor which, in response to a perceived stimulus, autophosphorylates on a histidine residue and transfers this phosphate group to an aspartate residue of a specific regulator, which modulates the expression of target genes necessary for adaptation.

Dickeya dadantii is one of the ten most feared broad host spectrum plant pathogenic bacteria in the world. D. dadantii enters a wounded plant and starts to colonize its apoplast by reacting to the plant's defenses: nothing seems to happen, this is the asymptomatic phase. In case of success, the bacterium increases considerably the secretion of enzymes leading to cell lysis, migrates and multiplies throughout the plant causing the so-called soft rot of the plant tissues: this is the symptomatic phase.

Our objective is therefore to decipher the role(s) of the 32 TCS of D. dadantii in virulence, their interactions and to attribute to each of them their activation stimulus(s). To this end, and to solve the problem of the extreme lability of the phosphate bonds of these systems (the main obstacle to their study), we have developed an original technique that allows us to study them not only in vitro but also and especially within the infected host. Thus, we follow, step by step throughout the infection, the variation of the phosphorylation of each TCS allowing us to assign its temporality in planta and its function in vitro. 

Mucus is the first continuous physical barrier between the epithelium and microorganisms and other harmful substances in the intestinal lumen. Mucins, the major glycoproteins of mucus, are formed by a peptide axis with hundreds of different glycan chains. They have a wide range of biological functions that ensure the maintenance of cellular homeostasis and allow a mutually beneficial symbiosis with the microbiota. Many pathologies (cancerous, inflammatory or infectious) are associated with alterations in the expression and glycosylation of mucins. In our team, we aim to understand the molecular mechanisms leading to such alterations and to decipher the new functions exerted by the altered mucins.

More precisely, our first objective is to identify the mechanisms put in place by pathogens to modulate host mucins during infection in order to create a favorable niche for themselves and, in response, the mechanisms put in place by the mucus to regulate microbial virulence. Our second objective is to define if the alterations (neo-expressed mucins or specific O-glycans) have a diagnostic, prognostic or therapeutic value for the treatment of respiratory and intestinal pathologies.

In order to characterize the alterations and to study their roles, mucins are systematically purified from human and animal tissues in healthy and pathological conditions such as colorectal cancer, inflammatory bowel diseases, irritable bowel syndrome, cystic fibrosis, bacterial infections (Pseudomonas aeruginosa, Staphylococcus aureus, Helicobacter pylori, Streptococcus gallolyticus... ) and viral infections (Sars-Cov2). These mucins are then used to determine their glycosylation repertoire by state-of-the-art mass spectrometry techniques. They are also used i) for bacterial adhesion assays (by ELISA, on nitrocellulose membrane, on cells or tissues, by surface plasmon resonance...); ii) to develop glyco- or peptido-mimetics that block the interaction of bacterial adhesins or viral proteins with mucins; iii) to evaluate their potential as biomarkers of intestinal diseases.