The DNA fragment containing the phoA of Klebsiella pneumoniae was cloned into pACYC184. The size of the insert. was 4.0 kb and the restriction map showed it contained 3 Pstl sites and 4 PvuLI sites. The nucleotide sequence of the phoA region was determined, which showed strong (80%) sequence similarity with that of Escherichia coli. This suggested that these two species are phylogenetically very close to each other.