Chemotactic behaviour of Escherichia coli at high cell density

Remy Colin,Victor Sourjik,Knut Drescher

doi:10.1038/s41467-019-13179-1

Abstract

At high cell density, swimming bacteria exhibit collective motility patterns, self-organized through physical interactions of a however still debated nature. Although high-density behaviours are frequent in natural situations, it remained unknown how collective motion affects chemotaxis, the main physiological function of motility, which enables bacteria to follow environmental gradients in their habitats. Here, we systematically investigate this question in the model organism Escherichia coli, varying cell density, cell length, and suspension confinement. The characteristics of the collective motion indicate that hydrodynamic interactions between swimmers made the primary contribution to its emergence. We observe that the chemotactic drift is moderately enhanced at intermediate cell densities, peaks, and is then strongly suppressed at higher densities. Numerical simulations reveal that this suppression occurs because the collective motion disturbs the choreography necessary for chemotactic sensing. We suggest that this physical hindrance imposes a fundamental constraint on high-density behaviours of motile bacteria, including swarming and the formation of multicellular aggregates and biofilms.

Highlights

At high cell density, swimming bacteria exhibit collective motility patterns, self-organized through physical interactions of a still debated nature
The principles of bacterial chemotactic sensing are fairly well understood for a single cell[29,31], little was known about the effects of physical interactions between cells on chemotaxis, despite their frequent occurrence during self-concentration processes[38,39,40,41,42,43] and high-density collective motility[4,5,10]
We observed that the size of bacterial flow structures in fully developed collective motion is set by the smallest system size, the channel height, independently of cell length and volume fraction, and that an increasing amount of the kinetic energy of the system gets poured into this flow structure as the cell density increases

Summary

Introduction

At high cell density, swimming bacteria exhibit collective motility patterns, self-organized through physical interactions of a still debated nature. Very little is known about how the high-density physical interactions and the resulting collective motion influence the chemotactic navigation of bacteria[44,45]: for example, it is unclear whether chemotaxis would be improved by alignments of convective flows with the gradient[19,45] or instead compromised by random collisions between cells. This lack of knowledge is in part due to the technical difficulty of measuring the dynamics of cells in a dense suspension[20]. These results have important implications for collective behaviours of motile bacteria at high density

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