Imaging the emergence of bacterial turbulence: Phase diagram and transition kinetics

Abstract

We experimentally study the emergence of collective bacterial swimming, a phenomenon often referred to as bacterial turbulence. A phase diagram of the flow of 3D Escherichia coli suspensions spanned by bacterial concentration, the swimming speed of bacteria, and the number fraction of active swimmers is systematically mapped, which shows quantitative agreement with kinetic theories and demonstrates the dominant role of hydrodynamic interactions in bacterial collective swimming. We trigger bacterial turbulence by suddenly increasing the swimming speed of light-powered bacteria and image the transition to the turbulence in real time. Our experiments identify two unusual kinetic pathways, i.e., the one-step transition with long incubation periods near the phase boundary and the two-step transition driven by long-wavelength instabilities deep inside the turbulent phase. Our study provides not only a quantitative verification of existing theories but also insights into interparticle interactions and transition kinetics of bacterial turbulence.

Weakly nonlinear analysis of pattern formation in active suspensions

“…For example, motile bacteria such as E. coli and Bacillus subtilis propel themselves through their surrounding fluid environment, interacting through their induced flow fields (Pedley & Kessler 1992;Mendelson et al 1999;Lauga & Powers 2009;Lushi, Wioland & Goldstein 2014), while likewise immersed microtubule bundles slide and extend, driven by ATP-driven molecular motors (Sanchez et al 2012;Henkin et al 2014;DeCamp et al 2015;Needleman & Dogic 2017;Opathalage et al 2019). These active suspensions are remarkable because, despite the near lack of inertial effects relative to viscous ones, the activity of the particles can produce large-scale coherent flows and even so-called active or bacterial turbulence, characterized by chaotic fluctuations in particle concentration and fluid velocity (Simha & Ramaswamy 2002;Dombrowski et al 2004;Sokolov et al 2007;Zhang et al 2010;Sokolov & Aranson 2012;Dunkel et al 2013;Gachelin et al 2014;Thampi, Golestanian & Yeomans 2014;Doostmohammadi et al 2017;Nishiguchi et al 2017;Stenhammar et al 2017;Peng, Liu & Cheng 2021).…”

Response of vesicle shapes to dense inner active matter

“…Based on this velocity field, we calculate o z (r) = q x v y À q y v x , which is the local in-plane kinetic energy and vorticity. 28,29 As shown in Fig. 3(a), we observe bacterial various types of bacterial collective motion.…”

“…Based on this velocity field, we calculate ω z ( r ) = ∂ x v y − ∂ y v x , which is the local in-plane kinetic energy and vorticity. 28,29…”

Crack patterns of drying dense bacterial suspensions

“…4a shows the two-dimensional (2D) flow field of a suspension of wild-type swimmers near the compaction front during drying, which exhibits the characteristic swarming vortices induced by bacterial collective swimming. 4,5 Such a coherent dynamic structure was preserved throughout the drying course and gave rise to the local order packing of bacteria in the dried deposit as indicated by the red arrows in Fig. 4b.…”