Genetic analysis of an Escherichia coli urease locus: evidence of DNA rearrangement.

Ureolytic Escherichia coli strains are uncommon clinical isolates. The urease phenotype in a large percentage of these isolates is unstable and lost upon storage. We examined two urease-positive uropathogenic E. coli isolates that give off urease-negative segregants and determined that the urease phenotype was chromosomally encoded. The urease phenotype was cloned from E. coli 1021 and found to be encoded on a 9.4-kilobase HindIII restriction fragment. Transposon mutagenesis indicated that at least 3.2 kilobases of this fragment were necessary for production of urease. The urease recombinant plasmid pURE coded for at least four insert-specific polypeptides as determined by maxicell analysis. Disruption of the region encoding two of these polypeptides (67 and 27 kilodaltons) abolished urease activity. Analysis by Southern hybridization of urease-positive E. coli 1021 and seven independently isolated urease-negative segregants showed that a DNA rearrangement was associated with the urease-negative phenotype.