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. 2019 Dec 23;117(1):595–601. doi: 10.1073/pnas.1910849117

Fig. 1.

Fig. 1.

Nutrient-dependent costs and benefits of motility in the presence of introduced gradients. (A) Schematics illustrating growth-rate dependent partitioning of the cellular protein budget into different functional sectors, as well as coutilization of 2 different nutrients (triangles and squares) regulated by cAMP (small circles). Also indicated is chemotaxis-mediated enhancement of nutrient uptake. (B) Relation between growth rate, denoted as nutritional (N-) value of the carbon source and motility gene expression. Cells were cultured with shaking (180 r.p.m.) in minimal medium containing different carbon sources as indicated (Rib: 20 mM ribose, α-KG: 12 mM α-ketoglutarate, Suc: 15 mM succinate, Gro: 0.4% glycerol, GlcA: 20 mM gluconate, Fru: 20 mM fructose, Mal: 0.2% maltose, Ara: 20 mM arabinose, Glc: 0.4% glucose). Expression of Ptar-GFP reporter and growth rate were measured at log phase of growth using plate reader (see Methods and SI Appendix, Supplementary Text). Solid line shows resource allocation model with 2 fitting parameters as detailed in SI Appendix, Supplementary Text; zero promoter activity is predicted at the N-value of 1.03. (C and D) Growth competition in the coculture of motile WT cells (expressing CFP) and nonmotile ΔflhC cells (expressing YFP), with flhDC expressed either under native promoter (solid diamonds) or under Ptac (open diamonds) promoter induced with 10 µM IPTG. Shown is fraction (in %) of the WT cells in a mixed population grown for 72 h without shaking in the absence (C) or in the presence (D) of a bead containing 12% casein hydrolysate. N-values were taken from B. (E) Same as D, but for competition between WT and ΔcheY cells. Solid lines show fit to the data using simulations of 2-compartment chemotaxis model (black) and prediction of the full 2D model (green) as detailed in SI Appendix, Supplementary Text. Cartoon in D and E illustrates emergence of gradients of casein hydrolysate from an introduced bead. In all competition experiments, both strains were initially inoculated at a 1:1 ratio.