From the single mutant strains Δ<i>cyaA</i>, the first step was to remove the Kan cassette in order to create the recipient strain. The second step is using the P1 bacteriophage to transfer a Kan cassette from another bacteria to this recipient strain, in order to replace the second gene. The phage is grown on a strain containing the Kan cassette (Δ<i>araC</i> or Δ<i>envZ</i>), and the resulting phage lysate, wich contains phage DNA and bacterial DNA, is used to infect the recipient strain. Genetic recombination, catalyzed by enzymes of the recipient strain, incorporates the bacterial fragments into the recipient chromosome.