Journal: Environmental Microbiology

Article Title: Optimal Cell Length for Exploration and Exploitation in Chemotactic Planktonic Bacteria

doi: 10.1111/1462-2920.70021

Figure Lengend Snippet: Chemotactic responses in example populations of E. coli of different cell lengths in a microfluidic device creating a linear gradient of MeAsp. (a) Schematic of the microfluidic device used for the chemotactic assays. (b) Epifluorescence microscope image of a gradient of fluorescein in the microfluidic device showing the entire width of the central channel where bacteria are located, and partially the lateral channels were buffers with different amounts of chemoattractant are flowing. Vertical dashed red lines mark the limits of the channels. Superimposed in green is the profile of average fluorescein concentration (in arbitrary units of fluorescence intensity). (c–e) statistical distributions for cells in three different cell‐length classes exposed to a linear MeAsp gradient (∇ C / C = −1.2 mm −1 ): in purple, cells between 1.4 and 2.0 μm long, the most abundant length class in the untreated E. coli population; in red cells between 4.2 and 6.2 μm, the most abundant 2 h after treatment with cephalexin; in orange, cells between 10.8 and 15.6 μm, the most abundant 3 h after treatment. Data is aggregated for the entire duration of the experiment, between 10 and 60 min. (c) Bacterial cell densities across the width of the central channel. Circles are empirical measurements; continuous lines are nonlinear least squares exponential fits. (d) Inverse cumulative frequency of run times for cells swimming upgradient (continuous lines) and downgradient (dashed lines) with a maximum deviation of 45° from the direction of the gradient. (e) Polar frequencies of the average run speeds per the mean direction of the runs.

Article Snippet: We imaged cells in a phase contrast inverted microscope (Zeiss AxioVert A1) equipped with a temperature‐controlled stage (PE100‐ZAL System, Linkam Scientific Instruments Ltd., Tadworth, UK) and using a 10× objective (0.55 NA), which gave a depth of field of 12.4 μm.

Techniques: Microscopy, Bacteria, Concentration Assay, Fluorescence