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Title: Density fluctuations and energy spectra of 3D bacterial suspensions
Giant number fluctuations are often considered as a hallmark of the emergent nonequilibrium dynamics of active fluids. However, these anomalous density fluctuations have only been reported experimentally in two-dimensional dry active systems heretofore. Here, we investigate density fluctuations of bulk Escherichia coli suspensions, a paradigm of three-dimensional (3D) wet active fluids. Our experiments demonstrate the existence and quantify the scaling relation of giant number fluctuations in 3D bacterial suspensions. Surprisingly, the anomalous scaling persists at small scales in low-concentration suspensions well before the transition to active turbulence, reflecting the long-range nature of hydrodynamic interactions of 3D wet active fluids. To illustrate the origin of the density fluctuations, we measure the energy spectra of suspension flows and explore the density–energy coupling in both the steady and transient states of active turbulence. A scale-invariant density-independent correlation between density fluctuations and energy spectra is uncovered across a wide range of length scales. In addition, our experiments show that the energy spectra of bacterial turbulence exhibit the scaling of 3D active nematic fluids, challenging the common view of dense bacterial suspensions as active polar fluids.  more » « less
Award ID(s):
2028652
PAR ID:
10350802
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Soft Matter
Volume:
17
Issue:
48
ISSN:
1744-683X
Page Range / eLocation ID:
10806 to 10817
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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