Journal: Proceedings of the National Academy of Sciences of the United States of America

Article Title: Speed-dependent chemotactic precision in marine bacteria

doi: 10.1073/pnas.1602307113

Figure Lengend Snippet: Hydrogel-based microfluidic device used to quantify the chemotactic response of V. alginolyticus in a steady, linear concentration profile of serine. Channel D is the test channel (width W = 600 µm), where bacteria reside and are observed by video microscopy. Inlets are marked by a “1,” outlets by a “2.” Channel A is the source channel, carrying 500 nM serine, and channel B is the sink channel, carrying buffer (0 nM serine). Channel C is used before the experiments, for the fabrication of two 200-µm-wide hydrogel walls by injection of liquid agarose between arrays of PDMS pillars used for containment (Materials and Methods). Once agarose solidifies, it results in two hydrogel walls separating the test channel from the source and sink channels (Inset), which are permeable to diffusion of serine and thus enable the formation of a linear serine concentration profile, C(x) (from 100 to 400 nM), across the test channel (x direction; Inset and Fig. S2). All channels are 100 µm deep. During an experiment, the inlet D1 and the outlet D2 are sealed with glass coverslips to create a flow-free condition in the test channel. The imaging window covers the whole width W (600 µm) of the test channel and cells were imaged at 15 locations along the length of the test channel.

Article Snippet: Bacteria were imaged at 22 frames per second by phase contrast microscopy (Nikon Ti-E; 20×, 0.45 N.A.).

Techniques: Concentration Assay, Bacteria, Microscopy, Injection, Diffusion-based Assay, Imaging