Intermittent turbulence in flowing bacterial suspensions.
Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence with important implications for chemical and biological transport, yet this analogy has remained primarily qualitative. Here, we present experiments in which a dense suspension of Bacillus subtilis bacteria was flowed through microchannels and the velocity statistics of the flowing suspension were quantified using a recently developed velocimetry technique coupled with vortex identification methods. Observations revealed a robust intermittency phenomenon, whereby the average velocity profile of the suspension fluctuated between a plug-like flow and a parabolic flow profile. This intermittency is a hallmark of the onset of classic turbulence and Lagrangian tracking revealed that it here originates from the presence of transient vortices in the active, collective motion of the bacteria locally reinforcing the externally imposed flow. These results link together two entirely different manifestations of turbulence and show the potential of the microfluidic approach to mimic the environment characteristic of certain niches of the human microbiome.
Department of Chemistry (CMIC), Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA.
Eleonora
E
Secchi
Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA Department of Civil, Environmental and Geomatic Engineering, Institute for Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Roberto
R
Rusconi
Department of Chemistry (CMIC), Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy.
Stefano
S
Buzzaccaro
Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA Department of Civil, Environmental and Geomatic Engineering, Institute for Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland.
M Mehdi
MM
Salek
Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA Department of Civil, Environmental and Geomatic Engineering, Institute for Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Steven
S
Smriga
Department of Chemistry (CMIC), Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy.
Roberto
R
Piazza
Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA Department of Civil, Environmental and Geomatic Engineering, Institute for Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland romanstocker@ethz.ch.
Roman
R
Stocker
D001412:Bacillus subtilis / Q000502:physiology*; D000069196:Gastrointestinal Microbiome / Q000502:physiology; D006801:Humans; D008124:Locomotion / Q000502:physiology*; D013535:Suspensions
D013535:Suspensions
bacterial turbulence; collective dynamics; microfluidics