Fig. 1

Schematic representation of the self-made device used for the evolution of Bacillus siamensis A72. The “a” container used for supplying the fresh medium for the evolution experiment. The “b” container used for culturing the strains at different saline concentrations. The “c” container used for collecting discarded evolution cultures. “x%” represents initial saline concentration. “n” represents transfer times. Cells were inoculated into “b” container with 30 mL medium containing x% (w/v) saline, to an initial OD600nm of approximately 0.3, cultured at 30 °C, and dissolved in oxygen by magnetic bar stirring. When the OD600nm value reached 5.0–8.0, approximately 25 mL of the culture was pumped out from the “b” container to “c” container, and 25 mL of fresh medium from the “a” container was pumped into “b” container. For each passage, 1.0 mL of the culture was stored in 30% (v/v) glycerol at −80 °C for subsequent experiments. When the medium (1000 mL) in “a” container was exhausted, refilled sterile fresh medium with the saline concentration increased by 1%. When the cells could no longer grow at a specific saline concentration in ISP-50-S medium, the ALE experiment was terminated, “n-1” passage cultures were used for selecting desire mutants