M9 medium

The preparation of semisolid “swimming” agar plates was carried out according to Tremblay et al. [41] (link). M9-medium, consisting of the following salts Na₂HPO₄, KH₂PO₄, NaCl and NH₄Cl (all purchased from VWR Germany) diluted in aqua dest., and the supplements MgSO₄, CaCl₂ and glucose-monohydrat were pipetted to 0.3% Bacto agar (BM, Becton) dissolved in aqua dest. The solution was then filled into petri dishes and dried under laminar flow. The semisolid agar plates were used on the same day as preparation. For the motility-tests overnight cultures of the different strains were diluted in fresh LB broth and incubated for additional 2 h at 37°C. 10 µl of this bacterial suspension was inoculated in the middle of a semisolid agar plate and incubated at 37°C for 48 h. Experiments were repeated three times and the reported values represent the average. Error bars reflect the standard deviations.

All the chemicals, reagents, bacterial growth media such as H₂O₂ and NaOCl solution, LB medium, M9 medium, chloramphenicol, β-D-1-thiogalactopyranoside (IPTG) were purchased from VWR International (Radnor, PA, USA). The ASKA library and Keio collection were originally from the Coli Genetic Stock Center at Yale University. The no-insert control of pCA24N was from our previous study [23 (link)]. The plasmids with candidate genes were purified from candidate strains individually by Qiagen Miniprep plasmid purification kits (Hilden, Germany) and transformed into MG1655 cells by Bio-Rad Pulser™ Transformation Apparatus (Hercules, CA, USA).