Fast, high-throughput measurement of collective behaviour in a bacterial population

Abstract

Swimming bacteria explore their environment by performing a random walk, which is biased in response to, for example, chemical stimuli, resulting in a collective drift of bacterial populations towards 'a better life'. This phenomenon, called chemotaxis, is one of the best known forms of collective behaviour in bacteria, crucial for bacterial survival and virulence. Both single-cell and macroscopic assays have investigated bacterial behaviours. However, theories that relate the two scales have previously been difficult to test directly. We present an image analysis method, inspired by light scattering, which measures the average collective motion of thousands of bacteria simultaneously. Using this method, a time-varying collective drift as small as 50 nm s 21 can be measured. The method, validated using simulations, was applied to chemotactic Escherichia coli bacteria in linear gradients of the attractant a-methylaspartate. This enabled us to test a coarse-grained minimal model of chemotaxis. Our results clearly map the onset of receptor methylation, and the transition from linear to logarithmic sensing in the bacterial response to an external chemoeffector. Our method is broadly applicable to problems involving the measurement of collective drift with high time resolution, such as cell migration and fluid flows measurements, and enables fast screening of tactic behaviours.

Networked Chemoreceptors Benefit Bacterial Chemotaxis Performance

“…6A) depends on its ability to detect a meaningful concentration change over its run length ℓ 0 (10 to 30 μm for E. coli ) (1). The efficiency of detection depends on the attractant concentration C ( d , t ) and its local gradient ΔC ( ℓ 0 )/ C at the location of the cell (38–40). However, in the case of a gradient emanating from a local source, these quantities are correlated.…”

Dark-field differential dynamic microscopy

“…To date, differential dynamic analysis has been successfully applied to bright-field, [16][17][18][19]22,28 fluorescence, 16 confocal, 21 , polarised, 24 and phase-contrast 20,23,25 forms of microscopy. One widely used imaging mode that is not included in this list is darkfield microscopy, the illumination system for which is depicted in Fig.…”

“…15 From DDM, it is possible to obtain the same dynamical correlation function measured in dynamic light scattering as a function of wave vector (q) space in systems that are not compatible with DLS, and using smaller sample volumes. Since its original development, DDM has been successfully used to measure particle diffusivity, 16 particle velocity, 17 colloidal aggregation and gelation kinetics, 18,19 bacterial motility, [20][21][22][23] hydrodynamic factors in concentrated colloidal dispersions, 21 viscoelasticity of liquid crystals, 24 and anisotropic particle motion. 25 It has also been adapted for use in texture analysis microscopy.…”

Investigating the Swimming of Microbial Pathogens Using Digital Holography

“…This equipment is often used for routine sample screening and documentation, but provides other opportunities for quantitative measurements. Video tracking of particles or cells [5] gives a single-cell resolution picture of motility, while scattering-based methods can assay motility in a larger population [6,7]. Another example is digital inline holographic microscopy (DIHM).…”