New gentamicin-resistance and lacZ promoter-probe cassettes suitable for insertion mutagenesis and generation of transcriptional fusions.

A set of antibiotic-resistance and promoter-probe cassettes suitable for insertion mutagenesis and generation of transcriptional fusions was constructed. The cassettes contain the aacC1 gene of transposon Tn1696 conferring resistance to gentamicin in a large variety of Gram- and Gram+ bacteria. In addition to the antibiotic-resistance gene, a promoterless Escherichia coli lacZ gene was included in the cassettes, allowing the determination of the transcriptional activity at the insertion site. The cassettes can be excised from a plasmid mediating ampicillin resistance by many commonly used restriction enzymes. The new constructs have been successfully used for mutagenesis and studies of gene transcription in Rhizobium meliloti.