Plasmid- and chromosome-coded aerobactin synthesis in enteric bacteria: insertion sequences flank operon in plasmid-mediated systems

Abstract

Large plasmids were detected in 2 aerobactin-producing enteric bacterial species (Aerobacter aerogenes 62-I, Salmonella arizonae SA1, and S. arizonae SL5301) and designated pSMN1, pSMN2 and pSMN3, respectively. S. arizonae SL5302, S. arizonae SLS, S. austin and S. memphis formed aerobactin but contained no detectable large plasmids. S. arizonae SL5283 made no aerobactin. A probe consisting of the aerobactin biosynthetic genes cloned on plasmid pABN5 hybridized to a HindIII digest of pSMN1 but not to digests of pSMN2 or pSMN3. A larger probe, the insert of pABN1 containing the complete aerobactin operon, hybridized to 4 fragments in HindIII digests of the parent plasmid, pCOlV-K30. A 2.0-kilobase PvuII fragment responsible for this multiple-hybridization pattern was cloned into vector pUC9 to form pSMN30. The latter was mapped and shown to correspond to either IS1 or to a closely related insertion sequence.