Swimming bacteria constantly move and consume their resources to find the best growth conditions. This continuous energy expense leads to fascinating statistical properties that do not have a counterpart in equilibrium systems. For example, a homogeneous bacterial bath can rectify the motion of asymmetric objects like ratchets. In this project, we aim to use genetically engineered E. Coli bacteria which swimming speed can be locally controlled using spatially modulated light. By arbitrarily imposing spatial gradients of cell motility, we aim to control the movement of arbitrarily shaped objects by shifting the necessary spatial asymmetry from the object to the bacterial bath. While theoretical works already validated this hypothesis, experimental pieces of evidence are still lacking. The proposed project aims to fill this gap by measuring the motion of passive objects suspended in local gradients of bacteria motility. The outcomes of this project can create new exciting frontiers toward the field of self-assembly and drug-delivery.
Recently, it has been theoretically shown that a local gradient of pressure can be created when a swimming speed gradient is externally imposed in an active system, for instance, using light[19]. This effect is an out-of-equilibrium one that does not have a counterpart in non-living matter[2]. This unique phenomenon has not been demonstrated experimentally. This project aims to tackle this gap.
Works in this direction are exciting because: (i) it will broaden our understanding and control of the non-equilibrium dynamics of active microsystems. (ii) The possibility of orchestrating the local gradients of pressure in an active bath by controlling their local speed opens up new possibilities for the transport of arbitrarily shaped objects by transferring the required broken spatially symmetry from the object to the bath. The outcomes of this project can create new exciting frontiers toward the field of self-assembly and drug-delivery[10].
Complete bibliography
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[3] Cates, M. E. Diffusive transport without detailed balance in motile bacteria: does microbiology need statistical physics? Reports on Progress in Physics 75, 042601 (2012).
[4] Bechinger, C. et al. Active particles in complex and crowded environments. Reviews of Modern Physics 88, 045006 (2016).
[5] Galajda, P., Keymer, J., Chaikin, P. & Austin, R. A
wall of funnels concentrates swimming bacteria. Journal
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[6] Kaiser, A. et al. Transport powered by bacterial turbulence.Physical review letters 112, 158101 (2014).
[7] Di Leonardo, R. et al. Bacterial ratchet motors. Proceedings of the National Academy of Sciences 107, 9541-9545 (2010).
[8] Marchetti, M. C. et al. Hydrodynamics of soft active matter. Reviews of Modern Physics 85, 1143 (2013).
[9] Koumakis, N., Lepore, A., Maggi, C. & Di Leonardo, R. Targeted delivery of colloids by swimming bacteria. Nature communications 4, 1-6 (2013).
[10] Whitesides, G. M. & Grzybowski, B. Self-assembly at all scales. Science 295, 2418-2421 (2002).
[11] Walter, J. M., Greenfield, D., Bustamante, C. & Liphardt,J. Light-powering escherichia coli with proteorhodopsin. Proceedings of the National Academy of Sciences 104, 2408-2412 (2007).
[12] Lozano, C., Ten Hagen, B., Löwen, H. & Bechinger, C. Phototaxis of synthetic microswimmers in optical landscapes. Nature communications 7, 1-10 (2016).
[13] Frangipane, G. et al. Dynamic density shaping of photokinetic e. coli. Elife 7, e36608 (2018).
[14] Arlt, J., Martinez, V. A., Dawson, A., Pilizota, T. & Poon, W. C. Painting with light-powered bacteria. Nature communications 9, 1-7 (2018).
[15] Vizsnyiczai, G. et al. Light controlled 3d micromotors powered by bacteria. Nature communications 8, 1-7 (2017).
[16] Stenhammar, J., Wittkowski, R., Marenduzzo, D. & Cates, M. E. Light-induced self-assembly of active rectification devices. Science advances 2, e1501850 (2016).
[17] Takatori, S. C., Yan, W. & Brady, J. F. Swim pressure: stress generation in active matter. Physical review letters 113, 028103 (2014).
[18] Yang, X., Manning, M. L. & Marchetti, M. C. Aggregation and segregation of confined active particles. Soft matter 10, 6477-6484 (2014).
[19] Solon, A. P. et al. Pressure is not a state function for generic active fluids. Nature Physics 11, 673-678 (2015).
[20] Arlt, J., Martinez, V. A., Dawson, A., Pilizota, T. & Poon, W. C. Dynamics-dependent density distribution in active suspensions. Nature communications 10, 1-7 (2019).
[21] Schwarz-Linek, J. et al. Escherichia coli as a model active colloid: A practical introduction. Colloids and Surfaces B: Biointerfaces 137, 216 (2016).
[22] Datsenko, K. A. & Wanner, B. L. One-step inactivation of chromosomal genes in escherichia coli k-12 using pcr products. Proceedings of the National Academy of Sciences 97, 6640-6645 (2000).