Escherichia coli chemotaxis to competing stimuli in a microfluidic device with a constant gradient

Abstract

In natural systems bacteria are exposed to many chemical stimulants; some attract chemotactic bacteria as they promote survival, while others repel bacteria because they inhibit survival. When faced with a mixture of chemoeffectors, it is not obvious which direction the population will migrate. Predicting this direction requires an understanding of how bacteria process information about their surroundings. We used a multiscale mathematical model to relate molecular level details of their twocomponent signaling system to the probability that an individual cell changes its swimming direction to the chemotactic velocity of a bacterial population. We used a microfluidic device designed to maintain a constant chemical gradient to compare model predictions to experimental observations. We obtained parameter values for the multiscale model of Escherichia coli chemotaxis to individual stimuli, α-methylaspartate and nickel ion, separately. Then without any additional fitting parameters, we predicted bacteria response to chemoeffector mixtures. Migration of E. coli toward α-methylaspartate was modulated by adding increasing concentrations of nickel ion. Thus, the migration direction was controlled by the relative concentrations of competing chemoeffectors in a predictable way. This study demonstrated the utility of a multiscale model to predict the migration direction of bacteria in the presence of competing chemoeffectors.

Chemorepellent-Loaded Nanocarriers Promote Localized Interference of Escherichia coli Transport to Inhibit Biofilm Formation

“…Of particular interest, the maximum GFP signal occurred at an average distance of 20 ± 5 μm away from the Ni NC coated glass. Chemorepellents bias the swimming behavior of single-cells that results in population-scale migration away from high chemorepellent concentrations . Therefore, the observed population-scale shift in E. coli GFP fluorescence signal away from Ni NC coated glass is characteristic of a chemorepellent response.…”

“…Escherichia coli HCB1 is a chemotactic, motile strain, previously obtained from Howard Berg’s lab and transformed to express GFP with the pGLO Bacterial Transformation Kit (Bio-Rad Laboratories) …”

“…Escherichia coli HCB1 is a chemotactic, motile strain, previously obtained from Howard Berg's lab and transformed to express GFP with the pGLO Bacterial Transformation Kit (Bio-Rad Laboratories). 44 E. coli HCB1 was stored at −80 °C in 20% (w/v) glycerol. E. coli HCB1 was inoculated from frozen stock into 50 mL of TB media in 250 mL baffled flasks and incubated overnight at 30 °C and 150 rpm.…”

“…Chemorepellents bias the swimming behavior of singlecells that results in population-scale migration away from high chemorepellent concentrations. 44 Therefore, the observed population-scale shift in E. coli GFP fluorescence signal away from Ni NC coated glass is characteristic of a chemorepellent response. Specifically, the observed bacterial depletion zone and bacterial accumulation away from the surface on ∼10 μm length scales are evidence of a highly localized chemorepellent response away from the Ni NC coated glass.…”

Repulsion from slow-diffusing nutrients improves chemotaxis towards moving sources

“…When faced with two opposing attractant gradients microbes must choose between the two, with outcomes potentially dependent on previous environmental exposure and resulting receptor expression [21][22][23] . In the presence of parallel attractant and repellant gradients, microbes must make a similar choice between net attraction or repulsion [24][25][26][27][28][29] , with chemotaxis to an intermediate distance from the source or a 'bet-hedging' split into attracted and repelled subpopulations also being possible outcomes 25 . In some cases, a microbe will only respond to one chemoeffector if another is present 18 .…”