Project description: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 P. aeruginosa in response to agmatine and putrescine with an emphasis in polyamine catabolism. Agmatine serves as precursor compound for putrescine (and hence spermidine and spermine), which was proposed to convert into GABA and succinate before entering the TCA cycle in support of cell growth as the sole source of carbon and nitrogen. Two acetylpolyamine amidohydrolases, AphA and AphB, were identified 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 indispensable for polyamine utilization. The newly identified dadRAX locus, encoding the regulator, alanine transaminase and racemase respectively, coupled with SpuC, the major putrescine-pyruvate transaminase, were key components to maintain alanine homeostasis. Corresponding mutant strains were severely hampered in polyamine utilization. On the other hand, the alternative gamma-glutamylation pathway for the conversion of putrescine into GABA was also discussed. Subsequently, GabD, GabT and PA5313 were identified for GABA utilization. Growth defect of 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 was also demonstrated in vitro. Polyamine utilization in general was proven independent of the PhoPQ two-component system even the expression of which was induced by polyamines. Multiple potent catabolic pathways as depicted in this study could serve pivotal roles in control of intracellular polyamine levels. Keywords: Metabolism, polyamines, agmatine, putrescine, glutamate, phoPQ.

Project description: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 P. aeruginosa in response to agmatine and putrescine with an emphasis in polyamine catabolism. Agmatine serves as precursor compound for putrescine (and hence spermidine and spermine), which was proposed to convert into GABA and succinate before entering the TCA cycle in support of cell growth as the sole source of carbon and nitrogen. Two acetylpolyamine amidohydrolases, AphA and AphB, were identified 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 indispensable for polyamine utilization. The newly identified dadRAX locus, encoding the regulator, alanine transaminase and racemase respectively, coupled with SpuC, the major putrescine-pyruvate transaminase, were key components to maintain alanine homeostasis. Corresponding mutant strains were severely hampered in polyamine utilization. On the other hand, the alternative gamma-glutamylation pathway for the conversion of putrescine into GABA was also discussed. Subsequently, GabD, GabT and PA5313 were identified for GABA utilization. Growth defect of 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 was also demonstrated in vitro. Polyamine utilization in general was proven independent of the PhoPQ two-component system even the expression of which was induced by polyamines. Multiple potent catabolic pathways as depicted in this study could serve pivotal roles in control of intracellular polyamine levels. Experiment Overall Design: P. aeruginosa PAO1 was grown aerobically in minimal medium P with 350 rpm shaking at 37C, in the presence of L-glutamate alone or with the addition of putrescine, agmatine or GABA at 20 mM. Cells were harvested when the optical density at 600 nm reached 0.5~0.6 by centrifugation for 5 minutes at 4C. Total RNA samples were isolated by RNeasy purification kit following instructions of the manufacturer (Qiagen). Reverse transcription for cDNA synthesis, fragmentation by DNase I treatment, cDNA probe labeling and hybridization were performed according to the instructions of GeneChip manufacturer (Affymetrix). Data were processed by Microarray Suite 5.0 software normalizing the absolute expression signal values of all chips to a target intensity of 500. GeneSpring software (Silicon Genetics) was used for expression pattern analysis and comparison. Only genes showing consistent expression profiles in duplicates were selected for further analysis.

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