Functional characterization of the agtABCD and agtSR operons for 4-aminobutyrate and 5-aminovalerate uptake and regulation in Pseudomonas aeruginosa PAO1.

Growth of Pseudomonas aeruginosa on diamines cadaverine, putrescine, and diaminopropane requires the γ-glutamylation pathway to convert these diamines into δ-aminovalerate (AMV), γ-aminobutyrate (GABA), and β-alanine. From DNA microarrays experiments the agtABCD operon (PA0603-0606) encoding components for an ABC transporter system was found inducible by exogenous AMV, GABA, and β-alanine, but not by diamines. Induction of the agtABCD operon was abolished in the mutants of upstream agtS (PA0600) or agtR (PA0601) genes encoding the membrane-anchored sensor and the response regulator of a two-component regulatory system, respectively. Growth phenotype analysis supports the physiological functions of these agt genes on utilization of AMV and GABA. Through measurements of β-galactosidase activities from an agtA::lacZ fusion, the requirement of a functional AgtS in control of the induction effect by exogenous AMV and GABA was further substantiated. The recombinant hexa-hisidine tagged agtR was constructed and purified to demonstrate its specific interactions with the agtA promoter region by electrophoretic mobility shift assays. In summary, this study establishes the functions of agtSR and agtABCD operons in AMV and GABA uptake, and provides a potential linkage between AMV/GABA metabolism and polymicrobial infection through the recently reported function of agtR in sensing of peptidoglycan shed by gram-positive bacteria (Korgaonkar et al., Proc Natl Acad Sci USA 110:1059-1064, 2013).