With the rationale provided in Fig. 1, plasmids p91BuOH(1)and p91BuOH(1)lptB were separately transformed into E. coli strain BW25113;deletion of the chromosomal lptB gene was performed via P1vir phage transduction. As expected, the strain that contained plasmid p91BuOH(1) was not viable due to the absence of either a chromosomal or plasmid-based essential lptB gene. However,plasmid p91BuOH(1)lptB rescued growth in the chromosomal lptB gene deletion mutant strain due to expression of the plasmid-based essential lptB gene,thus resulting in the construction of strain RKE01.