Bacterial strain, conjugal plasmid, and growth media.
Pseudomonas putida KT2440::lacIq1, harboring the conjugative plasmid pKJK10, was used as the donor strain. Plasmid pKJK10 is a derivative of the 54-kb natural rhizosphere plasmid pKJK5 carrying natural tetracycline resistance (30).
pKJK10 has the gfp(mut3b) gene inserted downstream of the lac-repressible promoter PA1-04/03 (22, 30).
The plasmid donor strain was grown in Luria-Bertani (LB) broth
The broth cultures were grown with vigorous shaking (250 rpm) at 30°C for 20 h.
The cells were washed twice and resuspended in sterile saline (9‰ NaCl).
The plasmid donor cells were verified for repression of the gfp gene by flow cytometry prior to inoculation into microcosms.