The proposed research programme aims at identifying noise-generating mechanisms in subsonic turbulent jets, and at the development of closed-loop control laws for the reduction of jet noise through flow actuation. An interdisciplinary approach combines experiment, numerical simulation and theoretical modelling in a coordinated effort, between three partner institutions with complementary expertise. While optimal control laws can, in principle and at enormous computational cost, be devised on the empirical basis of numerical simulations, taking into account the entire turbulent spectrum, the present proposal focuses on the dominant noise component associated with large-scale coherent flow structures, that drive the low-angle sound field. Fundamental progress in the understanding of the dynamics of these coherent structures, as well as their sound generation, will provide guidance for novel strategies to actively control and reduce jet noise. The programme addresses the following questions: Which mechanisms govern the formation of orderly structures in jet turbulence? Can these structures be accurately described as instability wavepackets forming on top of a steady mean flow, as has often been conjectured? To what extent do nonlinear phenomena determine the wavepacket structure and the resulting acoustic field? And how can knowledge of these mechanisms be leveraged for jet noise reduction? Control strategies will be devised, and these will be tested in a real experiment during the final stage of the project. The proposal builds on ongoing research activities at the three partner institutions, which so far have been developed independently without formal collaboration. The synergy potential of these complementary activities is considerable, and the proposal precisely aims to provide a framework for a coordinated interaction with a common set of objectives. Operational tools and preliminary results exist for all the main stages of the proposed programme. These include ongoing experiments on jet dynamics and their acoustic signature at PPRIME; a validated LES code; numerical tools for jet instability analysis at LadHyX, that are currently used on model configurations and await application on real-life jet data; model-free control concepts, developed at LadHyX, ONERA and LIMSI, that have been successfully deployed to reduce sound emission from flow over cavities; and reduced-order modeling for flow control (ANR Chair of Excellence at Pprime). International collaborations on jet noise research, with Tim Colonius at the California Institute of Technology and with André Cavalieri at Instituto Tecnológico de Aeronáutica (Sao José dos Campos, Brazil), are already in place and will be further intensified during the course of the proposed programme. The proposal seeks funding for (i) one PhD student (3 years) and four postdoc years; (ii) experimental equipment for particle image velocimetry in high-speed jets; (iii) travel expenses for conference participation and for the collaboration between partners, including the external collaborators at Caltech and at ITA.

Antimicrobial resistance is a major threat worldwide that requires a strong investment in fundamental studies. Resistance, as well as transient tolerance (persistence) to antibiotics, involve a network of intracellular stress responses: e.g., the stringent response, the SOS response, and the RpoS-regulated general stress response. We and others have shown that these stress responses are induced by antibiotic (AB) doses below the minimum inhibitory concentration (sub-MIC) and that they can accelerate acquisition of heritable AB resistance through increased mutagenesis and horizontal gene transfer (HGT). Although low concentrations of antibiotics do not kill bacteria, they can have a major impact on bacterial populations. In particular, it was shown that AB concentrations as low as hundred-fold below the MIC can lead to mutations and the selection of AB resistant cells. Most of the studies describing how bacteria acquire resistance or become persisters are based on experiments dealing with populations of cells. Such measurements yield average quantities for the whole population but they cannot provide a distribution of responses, nor can they follow the temporal evolution of individuals within the population. By contrast, there is mounting evidence that cells within a given population can display widely heterogeneous responses to an AB stress. This project aims at describing precisely individual cell fate during stress responses to low doses of antibiotics, and understanding the emergence of antibiotic resistance on the level of a single cell. We propose to address the profile of induction of four stress responses at the single-cell level: SOS, stringent response, RpoS general stress response and oxidative stress response, in response to three ABs from different families (fluoroquinolones, aminoglycosides, ß-lactams). To this end, we will use a microfluidic platform to culture bacteria, while submitting them to controlled AB stresses to assess heterogeneity and growth on chip. We will develop the theoretical description of bacterial growth dynamics taking into account the AB stress through mathematical modelling relating large-scale heterogeneity to the variability on the scale of individual cells. We will then isolate and extract cells that show phenotypic diversity. The large statistics will allow us to get access to rare events. The extracted cells will be subjected to analysis (NGS, dPCR) in order to detect horizontal gene transfers, mutations or changes of protein expression that can explain the behavior of these cells. This will first require the development of technological tools to genotype the small number of bacterial cells that can be recovered from the microchannel. The second step will be to explore different conditions that lead to the emergence of antibiotic resistance in order to gain insight into the underlying mechanisms and devise strategies to counter them. The impact of this project will be threefold: (i) Concerning the fundamental biological knowledge it will bring, (ii) the technological and quantitative developments that accompany it, and (iii) in understanding the emergence of resistance mechanisms and their implications for the development of new therapeutic strategies.

How do tissues and organs grow to reach well-defined shapes? For instance, thin tissues, such as animal epithelia and plant leaves, are typically flat, whereas the default state of a growing thin sheet is curved. How is flat shape achieved? Here we address this question in Arabidopsis leaves, a system amenable to live-imaging of growth, biophysical experiments, and genetic manipulation. We hypothesize that cell-to-cell growth heterogeneity enables cells to sense variations in leaf curvature and maintain flatness. We aim to test this hypothesis using experimental and theoretical biophysics with cell biology. We will (i) characterize the relationship between cell-to-cell heterogeneity, cell mechanics, and leaf flatness, (ii) build a theoretical framework to model a thin active growing sheet in 3D space, and (iii) characterize the combinatorial regulation of flatness through model predictions and experimental tests. Altogether, we expect to shed light on the robustness of morphogenesis.

The Cell Wall (CW) is a thin and stiff layer encasing and protecting bacterial, plant and fungal cells. It undergoes dynamic modifications in mechanics and composition that drive growth, reproduction, and infection. Such modifications entail risks of CW breakage and lysis of cells, due to their high internal pressure. In fungi, those risks are mitigated by the cell wall integrity pathway (CWI), which detects CW defects through membrane mechanosensors, and promotes compensatory responses. Building on novel quantitative approaches of our consortium to dynamically map CW mechanics around live fission yeast cells, and to model walled cells growth and morphogenesis, we propose an interdisciplinary program aiming at dissecting the mechanisms of CW mechanosensing by surface sensors of the CWI and at addressing the function of mechanosensation in cell growth. This project shall shed light on the mechanisms of surface mechanosensing and their role in promoting cell survival during growth.

Plants continuously develop throughout their lifetime through the apical meristems located at the tip of growing axes. The genetic regulation of the shoot apical meristems (SAMs), which produces all plant aerial parts, has been extensively studied in model plants, and various key molecular actors have been identified and mapped in space and time. Based on these results, recent works have investigated how these molecular actors induce physical deformation of tissues by modifying cell wall mechanical properties, and in turn result in leaf or flower primordia outgrowth. In most of these studies, cell turgor pressure, that drives wall deformation, is assumed to be constant and homogeneous. Here, with a pluri-disciplinary team, we want to map mechanical and hydraulic properties in tissues and develop computational models to better understand how water pressure builds up in meristem parts. We will challenge this view by using mutants and treatments modifying cell conductivity and mechanics.