Efficient generation of unmarked deletions in Legionella pneumophila.

Unmarked gene deletions facilitate studies of Legionella pneumophila multicomponent processes, such as motility and exonuclease activity. For this purpose, FRT-flanked alleles constructed in Escherichia coli using λ-Red recombinase were transferred to L. pneumophila by natural transformation. Resistance cassettes were then efficiently excised using the Flp site-specific recombinase encoded on a plasmid that is readily lost.