Laboratoire Matière et Systèmes Complexes

Jean-Baptiste Lugagne

Equipe Physique du Vivant

External long-term and real-time control of gene expression in bacteria.

Inducible promoters are now routinely used in systems and synthetic biology to understand and construct genetic regulatory networks. Because of the stochasticity of gene expression and its limited observability in cells, such uses have long remained limited to short term, full induction of populations of cells. Fine-tuning of in vivo protein levels in bacteria remains a challenge. Recent results show that gene expression levels can be precisely manipulated over extended periods of time using control theory, with either in silico feedback or open-loop control platforms. Externalizing the control system allows for more sophisticated control strategies and also a wider variety of dynamic perturbation, or programming, of the system of interest. With precise control of gene expression, the signal processing properties of a genetic circuit can be analyzed by measuring its dynamic input-output function. My goal is to develop a control platform for gene expression in bacteria, to obtain a simple, adaptive, and model-free control platform that can be easily transfered to different gene expression control problems. To prove that even easily adaptable and model-free controllers can control complex processes and bring quantitative genetic tinkering one step forward, I want to test this platform on a benchmark, multi-stable problem of gene expression control : The genetic toggle switch.

Henri Lhuissier

Equipe DSHE

Webbed Jet

A jet of a Newtonian liquid impinging on a wall at right angle spreads as a thin liquid sheet which preserves the radial symmetry of the jet. We observe that for a viscoelastic jet (solution of polyethylene glycol in water) this symmetry can break : Close to the wall, the jet develops radial wings (pointed out in (a), and seen from above, through a transparent wall, in (b)) which connect it to the sheet. We will discuss the mechanism of this surprising destabilization of the jet shape, which develops perpendicularly to the direction expected for bucking, and show how it organizes the flow in the sheet at a larger scale (a suspended Savart sheet is shown from a perpendicular view in (c)).