Transcriptome analysis of Pseudomonas aeruginosa PAO1 Response to L-Ala, L-Asn and L-Asp

P. aeruginosa possesses the ability to utilize a wild range of compounds as the sole source of carbon and nitrogen, including proteogenic amino acids. In particular, utilization of L-Asp and L-Asn is insensitive to carbon catabolite repression as strong growth retains in the cbrAB mutants devoid of the essential regulators for the activation of most catabolic genes. Transcriptome analysis and functional characterization were conducted to identify genes that participate in the catabolism, uptake, and regulation of these two amino acids. Through gene knockout and growth phenotype analysis, degradation of L-Asn to L-Asp was shown to be mediated by two asparaginases AsnA and AsnB, whereas only AnsB is required for the deamidation of D-Asn to D-Asp. While D-Asp is a dead-end product, conversion of L-Asp to fumurate is catalyzed by an aspartase AspA as further evidenced by enzyme kinetics. The results from the measurements of promoter-lacZ expression in vivo and mobility shift assays in vitro demonstrated that the asnR and aspR genes encode two transcriptional regulators in response to L-Asn and L-Asp, respectively, for the induction of the ansPA operon and the aspA gene. In addition, exogenous L-Glu also cause induction of the aspA gene, most likely due to its conversion to L-Asp by the aspartate transaminase AspC. Expression of several transporters were also found inducible by L-Asn and/or L-Asp, including AatJQMP for acid amino acids, DctA and DctPQM for C4-dicarboxylates, and PA5530 for C5-dicarboxylates. In summary, a complete pathway and regulation for L-Asn and L-Asp catabolism was established in this study. Cross induction of three transport systems for dicarboxylic acids may provide a physiological explanation for the insensitivity of L-Asn and L-Asp utilization to carbon catabolite repression.

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