ProfessorAlain Filloux

Overview


Our research project aims to tackle the problem of persistence and chronic infection by Pseudomonas aeruginosa. P. aeruginosa is a gram-negative bacterium found in various environments including soil, water and vegetation. Importantly it is an opportunistic human pathogen, responsible for numerous nosocomial infections in immuno-compromised patients. These infections are fatal in cystic fibrosis patients.Our project follows several research lines, which deal with essential molecular mechanisms involved in biofilm formation and type VI protein secretion. These two key processes are co-regulated and highly relevant for P. aeruginosa pathogenesis. The regulatory control involves signalling pathways associated with two-component regulatory systems and the intracellular second messenger c-di-GMP. We address these questions using multi-disciplinary approaches in molecular microbiology, genetics, cellular microbiology, structural biology and biochemistry.

(i) P. aeruginosa, such as most microbes exist as surface associated communities called « biofilms ». The biofilm lifestyle is an efficient means for microorganisms to maintain a protected niche. In humans, establishment of the biofilm leads to chronic bacterial infection. Biofilms have been shown to display increased resistance to antibiotic treatment and are recalcitrant to eradication via the immune system. To spawn novel communities in new locations, microorganisms must successfully transit from the biofilm to the planktonic growth state. Whereas molecular knowledge on the biofilm formation process is now increasingly available, how bacterial cells detach is largely unknown. However, a productive field of investigation is likely to be the identification of molecular targets, which induce natural dispersion of the biofilm and make the released planktonic bacteria accessible to efficient therapeutic treatments. Our group will focus on studying key regulators that are involved in the perception of environmental cues that induce biofilm formation or dispersion and on the characterization of the molecular determinants that mechanically contribute to biofilm development and subsequent disruption. In particular we study the Gac/Rsm pathway and how it is influenced by upstream sensors such as RetS and LadS. This central pathway is partly connected with c-di-GMP signalling and we study the molecualr links existing between these two and how it influences the switch between a motile and a sessile lifestyle.

(ii) P. aeruginosa is capable of releasing a wide variety of extracellular hydrolytic enzymes and to inject effectors within host cells for hijacking their signalling pathways. In all cases the secretion mechanism involves multi-protein complexes that are partly embedded within the bacterial cell envelope. Several of these systems have now been well characterized. The secretion of proteins is crucial for many aspects of bacterial pathogenesis since it mediates interaction with the host and contributes to colonization, survival and cytotoxicity. The type VI secretion system (T6SS), which we study in the laboratory, is found in several copies on the P. aeruginosa genome, and is widely distributed among bacterial pathogens. The functionaly and role of the T6SS in P. aeruginosa pathogenesis is many-fold and range from manipulation of eukaryotic host cell to killing of bacterial competitors. Our group is involved in the structural characterization of the supramolecular assembly constituting this nanomachine and in the identification of novel T6SS effectors. This is including discovery of novel bacterial toxins, which is highly relevant for the development of new antimicrobial strategies.