TY - JOUR A1 - Hintsche, Marius A1 - Waljor, Veronika A1 - Grossmann, Robert A1 - Kühn, Marco J. A1 - Thormann, Kai M. A1 - Peruani, Fernando A1 - Beta, Carsten T1 - A polar bundle of flagella can drive bacterial swimming by pushing, pulling, or coiling around the cell body JF - Scientific reports N2 - Bacteria swim in sequences of straight runs that are interrupted by turning events. They drive their swimming locomotion with the help of rotating helical flagella. Depending on the number of flagella and their arrangement across the cell body, different run-and-turn patterns can be observed. Here, we present fluorescence microscopy recordings showing that cells of the soil bacterium Pseudomonas putida that are decorated with a polar tuft of helical flagella, can alternate between two distinct swimming patterns. On the one hand, they can undergo a classical push-pull-push cycle that is well known from monopolarly flagellated bacteria but has not been reported for species with a polar bundle of multiple flagella. Alternatively, upon leaving the pulling mode, they can enter a third slow swimming phase, where they propel themselves with their helical bundle wrapped around the cell body. A theoretical estimate based on a random-walk model shows that the spreading of a population of swimmers is strongly enhanced when cycling through a sequence of pushing, pulling, and wrapped flagellar configurations as compared to the simple push-pull-push pattern. Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-16428-9 SN - 2045-2322 VL - 7 PB - Macmillan Publishers Limited, part of Springer Nature CY - London ER - TY - JOUR A1 - Bär, Markus A1 - Großmann, Robert A1 - Heidenreich, Sebastian A1 - Peruani, Fernando T1 - Self-propelled rods BT - insights and perspectives for active matter JF - Annual review of condensed matter physics N2 - A wide range of experimental systems including gliding, swarming and swimming bacteria, in vitro motility assays, and shaken granular media are commonly described as self-propelled rods. Large ensembles of those entities display a large variety of self-organized, collective phenomena, including the formation of moving polar clusters, polar and nematic dynamic bands, mobility-induced phase separation, topological defects, and mesoscale turbulence, among others. Here, we give a brief survey of experimental observations and review the theoretical description of self-propelled rods. Our focus is on the emergent pattern formation of ensembles of dry self-propelled rods governed by short-ranged, contact mediated interactions and their wet counterparts that are also subject to long-ranged hydrodynamic flows. Altogether, self-propelled rods provide an overarching theme covering many aspects of active matter containing well-explored limiting cases. Their collective behavior not only bridges the well-studied regimes of polar selfpropelled particles and active nematics, and includes active phase separation, but also reveals a rich variety of new patterns. KW - collective motion KW - statistical physics KW - biological physics KW - nonequilibrium physics KW - stochastic processes Y1 - 2019 U6 - https://doi.org/10.1146/annurev-conmatphys-031119-050611 SN - 1947-5454 SN - 1947-5462 VL - 11 SP - 441 EP - 466 PB - Annual Reviews CY - Palo Alto ER - TY - JOUR A1 - Großmann, Robert A1 - Aranson, Igor S. A1 - Peruani, Fernando T1 - A particle-field approach bridges phase separation and collective motion in active matter JF - Nature Communications N2 - Whereas self-propelled hard discs undergo motility-induced phase separation, self-propelled rods exhibit a variety of nonequilibrium phenomena, including clustering, collective motion, and spatio-temporal chaos. In this work, we present a theoretical framework representing active particles by continuum fields. This concept combines the simplicity of alignment-based models, enabling analytical studies, and realistic models that incorporate the shape of self-propelled objects explicitly. By varying particle shape from circular to ellipsoidal, we show how nonequilibrium stresses acting among self-propelled rods destabilize motility-induced phase separation and facilitate orientational ordering, thereby connecting the realms of scalar and vectorial active matter. Though the interaction potential is strictly apolar, both, polar and nematic order may emerge and even coexist. Accordingly, the symmetry of ordered states is a dynamical property in active matter. The presented framework may represent various systems including bacterial colonies, cytoskeletal extracts, or shaken granular media. Interacting self-propelled particles exhibit phase separation or collective motion depending on particle shape. A unified theory connecting these paradigms represents a major challenge in active matter, which the authors address here by modeling active particles as continuum fields. Y1 - 2020 U6 - https://doi.org/10.1038/s41467-020-18978-5 SN - 2041-1723 VL - 11 IS - 1 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Gómez-Nava, Luis A1 - Grossmann, Robert A1 - Hintsche, Marius A1 - Beta, Carsten A1 - Peruani, Fernando T1 - A novel approach to chemotaxis BT - active particles guided by internal clocks JF - epl : a letters journal exploring the frontiers of physics N2 - Motivated by the observation of non-exponential run-time distributions of bacterial swimmers, we propose a minimal phenomenological model for taxis of active particles whose motion is controlled by an internal clock. The ticking of the clock depends on an external concentration field, e.g., a chemical substance. We demonstrate that these particles can detect concentration gradients and respond to them by moving up- or down-gradient depending on the clock design, albeit measurements of these fields are purely local in space and instantaneous in time. Altogether, our results open a new route in the study of directional navigation: we show that the use of a clock to control motility actions represents a generic and versatile toolbox to engineer behavioral responses to external cues, such as light, chemical, or temperature gradients. Y1 - 2020 U6 - https://doi.org/10.1209/0295-5075/130/68002 SN - 0295-5075 SN - 1286-4854 VL - 130 IS - 6 PB - IOP Publ. Ltd. CY - Bristol ER -