Density Fluctuations and Energy Spectra of 3D Bacterial Suspensions

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

“…2D). Although the transition to bacterial turbulence has been investigated with increasing  and v in separate experiments (17,(26)(27)(28)(29)(30), to the best of our knowledge, systematic measurements over such a large parameter space in the same experimental system have not been achieved previously. This comprehensive 3D phase diagram not only allows us to quantitatively verify the theoretical prediction on the transition point but also sets up a framework for exploring the kinetics of the transition in the next section.…”

“…The length scales associated with the transition kinetics are revealed by the energy spectrum of bacterial flows, E(k), where k is the wave number (Materials and Methods) (3,28). E(k) is related to the energy density E through E = ∫ 0 ∞ E(k ) dk .…”

“…Pioneering experiments on suspensions of Bacillus subtilis first showed the emergence of bacterial turbulence at high concentrations in absence of bioconvection and chemotaxis (17,(24)(25)(26)(27). Various physical properties of bacterial turbulence such as density fluctuations (27,28), coherent flow structures (28)(29)(30)(31)(32), and mass and momentum transports (33)(34)(35)(36) have been subsequently studied. While most of these studies focused on the rise of bacterial turbulence with increasing bacterial concentrations, few experiments have considered other factors important for bacterial turbulence such as the swimming speed of bacteria (29,30) and the presence of defective immobile bacteria.…”

To cross or not to cross: collective swimming of Escherichia coli under two-dimensional confinement

“…In our experiments, we use genetically modified lightpowered E. coli (see Appendix A: Methods), whose average swimming velocity V can be controlled between 4 and 15 µm/s by varying the intensity of incident light [15,16]. In addition to bacterial swimming velocity, we also vary 2D bacterial number density n between 1.3 × 10 6 up to 2.6 × 10 7 mm −2 .…”

“…Consequently, understanding the collective dynamics of bacteria in confined systems is vital for deciphering various life-supporting activities of bacteria in their natural environments. However, although the collective dynamics of 3D bulk bacterial suspensions have been extensively studied in recent years [12][13][14][15][16], our understanding of the dynamics of bacterial suspensions under geometric confinement is still primitive.…”