Expression of the AsbA1, OXA-12, and AsbM1 beta-lactamases in Aeromonas jandaei AER 14 is coordinated by a two-component regulon

Aeromonas jandaei AER 14 (formerly Aeromonas sobria AER 14) expresses three inducible beta-lactamases, AsbA1, OXA-12 (AsbB1), and AsbM1. Mutant strains that constitutively overexpress all three enzyme simultaneously, suggesting that they share a common regulatory pathway, have been isolated. Detectable expression of the cloned genes of AsbA1 and OXA-12 in some Escherichia coli K-12 laboratory strains is achieved only in the presence of a blp mutation. These mutations map to the cre operon at 0 min, which encodes a classical two-component regulatory system of unknown function. Two regulatory elements from A. jandaei which permit high-level constitutive expression of OXA-12 in E. coli were cloned. Both loci encode proteins with characteristics of response regulator proteins of two-component regulatory systems. One of these loci, designated blrA, bestowed constitutive expression of all three beta-lactamases in A. jandaei AER 14 when present on a multicopy plasmid, confirming its role in the regulatory pathway of beta-lactamase production in this organism.