A 50x M9 medium (2385 mM Na2HPO4, 1100 mM KH2PO4, 427.75 mM NaCL, 935 mM NH4Cl, 100 mM MgSO4, 10 mM CaCl2) was prepared and diluted to the following concentrations; 40x, 30x, 20x, 10x, 5x, 1x, 0.5x. A final concentration of 2 mM glucose was added to each dilution. No growth was observed at 30x, 40x M9 (data not shown). For the experiment with NaCl concentrations, an M9 1x (47.7 mM Na2HPO4, 22 mM KH2PO4, 8.55 mM NaCL, 18.7 mM NH4Cl, 2 mM MgSO4, 0.2 mM CaCl2) was prepared with NaCl added to the following final concentrations: 2000 mM, 1000 mM, 500 mM, 100 mM, 10 mM. A final concentration of 2 mM glucose was added to each dilution. P. fluorescens A506 YFP and P. putida KT2440 YFP were grown overnight in LB gen 30µg/ml at 28°C, 300 RPM. 3 mL LB gen 30µg/ml was inoculated with 100μls of the overnight stock and grown until OD ~1.0. The bacteria were centrifuged, resuspended in DiH20, and diluted 1:20 once loaded into the 96-well plate. There were triplicates of each condition for A506 YFP and KT2440 YFP, and duplicates for the controls. Estimated growth rates, lag times, and maximal OD, based on the growth curves, are shown in Supplementary file 2.