Extended Data Fig. 1: Expansion speed measurements.

a, Temporal evolution of front position for a population of E. coli HE206 cells (wild type) grown on a soft-agar plate with saturating amounts of different carbon sources (see legend) and 100 μM aspartate as attractant. Lines show linear fits. Experiments were repeated at least twice with similar results. b, Temporal evolution of front position for HE443 cells grown on 40 mM glycerol and 100 μM aspartate with different amounts of the inducer 3MBA (see legend) that titrate glycerol uptake²⁶, resulting in different growth rates (Supplementary Table 2). The experiments were repeated at least twice with similar results. c, Expansion speed and its dependence on growth rate for the commonly used E. coli K-12 strain MG1655B⁷⁷ (red symbols) and the K-12 variant RP437 (blue symbols) frequently used in motility studies (see Supplementary Text 1.1). Growth conditions were changed by varying the carbon source (from lower to higher growth rates: acetate, mannose, glycerol, glucose; see legend). Aspartate (100 μM) was added as the attractant. For the experiments with RP437, four amino acids (methionine, leucine, threonine, histidine) were provided at 1 mM each in the medium to sustain cell growth. Data from Fig. 1c are shown in grey for comparison. Data points represent the mean of two biological replicates, except for growth rates in acetate and mannose, which were from a single experiment. d, Expansion speeds plotted against the batch culture growth rate for populations grown in glycerol, glucose or aspartate as the only carbon source, without supplement of additional attractant (purple symbols). Growth on serine is very slow (<0.1 h⁻¹) and is not shown on the plot. Expansion speeds were much slower in these media without chemoattractant supplement, even though glucose and aspartate are both attractants themselves^21,45. The same was observed for a Δtar knockout strain when both glycerol and aspartate were present (open triangle). See Supplementary Tables 2, 3 for data values and sample sizes. Data from Fig. 1c are shown in grey for comparison. e, f, The difference between migration with and without additional attractant is further illustrated for growth on glycerol when growth rates are titrated (e), and for expansion when other carbon sources are provided (f). Hashed bars highlight additional increase in expansion speed (red) and growth rate (blue) when attractant is provided. In each case, supplementing low amounts of attractant(s) greatly increases expansion speed without affecting growth rate much. The graphs were created based on mean values listed in Supplementary Tables 2, 3. g, Expansion speed and its dependence on growth rate when two attractants are present (20 mM glycerol + 100 µM aspartate + 100 µM serine, green symbols) or for complex medium (CAA + carbon source, orange symbols). Data for single attractants (from Fig. 1c) are shown for comparison (20 mM glycerol + 100 µM aspartate, red; 20 mM glycerol + 100 µM serine, blue). Lines indicate fits to square-root dependencies as anticipated from a simple scaling analysis (Extended Data Fig. 9d). Data points in asp + ser (green points) represent means of two biological replicates (n = 2), except for growth rates of HE433 and HE443, which were from a single experiment (n = 1).

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