(a-b) If not present in excess, amino acids can also limit growth of cells. Indeed, cells generate spatial gradients for all nutrients and metabolites in their microenvironment. The tradeoff between diffusion of a molecule and its uptake rate defines the properties of the gradient, thus gradients are expected to vary from one nutrient to another. In this setting, glucose and amino acids are important nutrients that can limit growth if present at too low concentrations. Glucose is required as a carbon source and the media must be supplemented with amino acids as the strain is an auxotroph. To determine the importance of amino acid concentration, we reduced the amino acid concentration to the standard concentration of SC media (called 1 × CSM in the main text). (c) The front velocity was lower at high glucose and low amino acid concentrations than in the case with high glucose and high amino acid concentrations. There was no significant difference up to about 1% w/vol (55.5 mM) glucose. Above that glucose concentration, front velocities increased with the glucose concentration at a high amino acid concentration (5 × CSM), whereas front velocity levels off at a low amino acid concentration (1 × CSM). Data comes from the bin closest to position 0 µm as measured in Figure 2c for each glucose concentration. Depending on the glucose concentration, minimum 5 to maximum 12 trajectories were measured (n = 5–12). Represented are means and standard deviations that contain ~15- ~ 30 velocity points each. (d) The same effect was observed for local velocities. There was almost no distinction between local velocities as the source concentration of glucose increased up to about 1% w/vol (55.5 mM), but the difference in local velocities was striking at higher glucose concentrations. Taken together, this means that glucose is the limiting nutrient in both 1 × and 5 × amino acid media, up to a glucose concentration of about 1% w/vol (55.5 mM). For the case of 5 × amino acid concentration, glucose remains the limiting factor for glucose concentrations used in this study. Data comes from >100 trajectories, depending on different glucose concentration. Velocity datapoints were then binned into 16 equally spaced position points. Represented are means and standard deviations of each bin.