Transcriptome analysis of agmatine and putrescine catabolism in Pseudomonas aeruginosa PAO1.

Polyamines (putrescine, spermidine, and spermine) are major organic polycations essential for a wide spectrum of cellular processes. The cells require mechanisms to maintain homeostasis of intracellular polyamines to prevent otherwise severe adverse effects. We performed a detailed transcriptome profile analysis of Pseudomonas aeruginosa in response to agmatine and putrescine with an emphasis in polyamine catabolism. Agmatine serves as the precursor compound for putrescine (and hence spermidine and spermine), which was proposed to convert into 4-aminobutyrate (GABA) and succinate before entering the tricarboxylic acid cycle in support of cell growth, as the sole source of carbon and nitrogen. Two acetylpolyamine amidohydrolases, AphA and AphB, were found to be involved in the conversion of agmatine into putrescine. Enzymatic products of AphA were confirmed by mass spectrometry analysis. Interestingly, the alanine-pyruvate cycle was shown to be indispensable for polyamine utilization. The newly identified dadRAX locus encoding the regulator alanine transaminase and racemase coupled with SpuC, the major putrescine-pyruvate transaminase, were key components to maintaining alanine homeostasis. Corresponding mutant strains were severely hampered in polyamine utilization. On the other hand, an alternative gamma-glutamylation pathway for the conversion of putrescine into GABA is present in some organisms. Subsequently, GabD, GabT, and PA5313 were identified for GABA utilization. The growth defect of the PA5313 gabT double mutant in GABA suggested the importance of these two transaminases. The succinic-semialdehyde dehydrogenase activity of GabD and its induction by GABA were also demonstrated in vitro. Polyamine utilization in general was proven to be independent of the PhoPQ two-component system, even though a modest induction of this operon was induced by polyamines. Multiple potent catabolic pathways, as depicted in this study, could serve pivotal roles in the control of intracellular polyamine levels.