SeMoVi Seminar, Fevruary 15 2017
Location : Salle René Char - La Rotonde - INSA de Lyon
|
14.00 - 15.00 |
Audrey Beaussart Université de Lorraine
|
Atomic Force Microscopy as a tool to study microbial adhesion |
|---|---|---|
|
15.00 - 15.30 |
Coffee break |
|
|
15.30 - 16.00 |
Laurence Lemelle ENS Lyon |
Host-cell surfaces alter bacterial swimming |
|
16.00 - 16.30 |
Luca Monticelli
MMSB |
Hydrophobic pollutants in lipid membranes – a simulation perspective |
| 16.30 - 17.00 |
General discussion |
Atomic Force Microscopy as a tool to study microbial adhesion
Microbial pathogens are highly complex and heterogeneous systems. Cell populations generally contain subgroups of cells which exhibit differences in growth rate as well as resistance to stress and drug treatment. In addition, individual cells are spatially organized and heterogeneous, and this cellular heterogeneity is used to perform key functions. This complexity emphasizes the need for single-cell analysis techniques in microbial research.
With its ability to observe and manipulate cellular systems at nanometer resolution and in physiological conditions, atomic force microscopy (AFM) offers unprecedented opportunities in microbiology and contributes to the birth of a new field ‘microbial nanoscopy’. Using topographic imaging, researchers can visualize the ultrastructure of live cells and their subtle modification under activity of antibacterial agents. Force spectroscopy with tips bearing bioligands offers a means to probe the localization and adhesion of single receptors on cells, such as cell adhesion proteins and antibiotic binding sites, while single-cell force spectroscopy quantifies the forces driving microbe-microbe, microbe-solid, and microbe-host interactions. In this talk, I will discuss how we can use these AFM modalities in microbiology. I will present some recent breakthroughs in pathogen research, emphasizing the potential of various AFM modes for studying cell adhesion and biofilm formation in Candida, Staphylococcus and Pseudomonas species.
Host-cell surfaces alter bacterial swimming
For most pathogenic bacteria, flagellar motility is recognized as a virulence factor. Here, we analysed the swimming behaviour of bacteria close to eukaryotic cellular surfaces, using the major opportunistic pathogen Pseudomonas aeruginosa as a model. We delineated three classes of swimming trajectories on both cellular surfaces and glass that could be differentiated by their speeds and local curvatures, resulting from different levels of hydrodynamic interactions with the surface. Segmentation of the trajectories into linear and curved sections or pause allowed us to precisely describe the corresponding swimming patterns near the two surfaces. We concluded that (i) the trajectory classes were of same nature on cells and glass, however the trajectory distribution was strikingly different between surface types, (ii) on cell monolayers, a larger fraction of bacteria adopted a swimming mode with stronger bacteria-surface interaction mostly dependent upon Type IV pili. Thus, bacteria swim near boundaries with diverse patterns and importantly, Type IV pili differentially influence swimming near cellular and abiotic surfaces.
Hydrophobic pollutants in lipid membranes – a simulation perspective
The first contact of exogenous materials with living organisms generally involves the interaction with a biological membrane. Understanding the interaction of exogenous materials with biological membranes is therefore a key step towards characterizing their biological activity. Cell membranes have a complex chemical composition and lateral organization, and are generally fluid under physiological conditions – which makes it extremely difficult to study their structure and dynamics experimentally. Molecular simulations on model membranes can aid in the interpretation of experimental data on membranes, including their structure, dynamics, and interactions. In this presentation I will describe the effect of six different hydrophobic pollutants on the properties of model membranes, and in particular on their lateral organization. Cell membranes have a complex lateral organization featuring domains with distinct composition, also known as rafts, playing an essential role in cellular processes. Perturbation of membrane domains has major effects on the activity of raft-associated proteins and on signaling pathways [1], but it is not clear which chemical and physical properties determine domain perturbation. Using molecular simulations on model membranes, we identified two groups of molecules with distinct behavior: aliphatic compounds promote lipid mixing by distributing at the interface between liquid-ordered and liquid-disordered domains; aromatic compounds, instead, stabilize phase separation by partitioning into liquid-disordered domains and excluding cholesterol from disordered domains [2,3]. We predict that relatively small concentrations of hydrophobic species can have a broad impact on domain stability in model systems, which suggests possible mechanisms of action for hydrophobic pollutants in vivo.
References
-
[1] K Simons, R Ehehalt, J Clin Invest (2002) 110, 597–603
-
[2] G Rossi, J Barnoud, L Monticelli, J Phys Chem Letters (2014) 5, 241-246
-
[3] J Barnoud, G Rossi, SJ Marrink, L Monticelli, PLoS Comp Biol. (2014) 10, e1003873
You can download the poster for that seminar here.
