Measurement of Bacterial Growth Curve

Bacterial growth curves were measured via the optical density value (OD₆₀₀) or the plate-counting method. In brief, an approximate dose of 10⁹ CFU bacteria grown to log-phase was rapidly added to an aseptic flask containing 100 ml of Martin's broth only or supplemented with a certain metabolite (n = 3 per group). The flasks were put into a shaker set to 37°C and speed at 220 rpm. Every 2 or 3 h, 1 ml of Martin's broth was taken aseptically and diluted to an appropriate dilution to estimate the optical density at 600 nm via using Vis Spectrophotometer (JINGHUA, China) or measure the bacteria number via the plate-counting method. Growth curves were drawn dependent on the results of different time points. The pH values were adjusted as above.