Amplification of nahAc from P. putida G7 with each of the nine possible combinations of three forward and three reverse primers. A single touchdown PCR temperature-cycling program was used. Lanes: 1 to 3, amplicons with primer Ac596R and primers Ab248F, Ac114F, and Ac307F, respectively; 4 to 6, amplicons with primer Ac893R and primers Ab248F, Ac114F, and Ac307F, respectively; 7 to 9, amplicons with primer Ac1095R and primers Ab248F, Ac114F, and Ac307F, respectively; M, HindIII-digested lambda DNA markers.