Construction of stable, single-copy luciferase gene fusions in Escherichia coli

A ColE1-based plasmid for transcriptional gene fusions was constructed that contains both the promoterless luxAB genes of Vibrio harveyi and a tet marker within the inverted repeats of a left end-truncated Tn5 element. Introduction of this plasmid into an Escherichia coli strain containing a plasmid (pTF421) that over-produces ColE1 RNA1 (and thus inhibits replication of the ColE1 plasmid) allowed selection for cells that had a single copy of the luxAB operon transposed into the chromosome beginning 5 days post-transformation. The long latent period necessary for Tn5 transposition is analogous to that found in other systems, where transposition frequencies and mutation rates increase in a time-dependent manner when selected for upon prolonged incubation on Petri dishes under bacteriostatic conditions.