FliA expression analysis and influence of the regulatory proteins RpoN, FleQ and FliA on virulence and in vivo fitness in Legionella pneumophila

In Legionella pneumophila, the regulation of the flagellum and the expression of virulence traits are linked. FleQ, RpoN and FliA are the major regulators of the flagellar regulon. We demonstrated here that all three regulatory proteins mentioned (FleQ, RpoN and FliA) are necessary for full in vivo fitness of L. pneumophila strains Corby and Paris. In this study, we clarified the role of FleQ for fliA expression from the level of mRNA toward protein translation. FleQ enhanced fliA expression, but FleQ and RpoN were not necessary for basal expression. In addition, we identified the initiation site of fliA in L. pneumophila and found a putative σ(70) promoter element localized upstream. The initiation site was not influenced in the ΔfleQ or ΔrpoN mutant strain. We demonstrated that there is no significant difference in the regulation of fliA between strains Corby and Paris, but the FleQ-dependent induction of fliA transcription in the exponential phase is stronger in strain Paris than in strain Corby. In addition, we showed for the first time the presence of a straight hook at the pole of the non-flagellated ΔfliA and ΔfliD mutant strains by electron microscopy, indicating the presence of an intact basal body in these strains

Generalized continua and phase-field models : application to crystal plasticity

International audienceThree continuum field theories are presented that account for the size-dependent behaviour of materials. The micromorphic medium is endowed with microdeformation degrees of freedom that describe the rotation and distortion of a triad of microstructural directions, like crystallographic lattice directions. It is a very general framework that can be specialized to strain gradient plasticity theory dedicated to the modelling of plastic events in metals and alloys. Both frameworks are developed here in the special case of crystal plasticity as a complete example of transition from micro-physical phenomena to continuum macro-modelling. Finally the phase field method is introduced in this landscape as a continuum modelling approach to the motion of phase boundaries and interfaces driven by thermodynamics and mechanics