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Abstract
d-Glu, an essential component of peptidoglycans, can be utilized as a carbon and nitrogen source by Pseudomonas aeruginosa. DNA microarrays were employed to identify genes involved in d-Glu catabolism. Through gene knockout and growth phenotype analysis, the divergent dguR–dguABC (d-Glu utilization) gene cluster was shown to participate in d-Glu and d-Gln catabolism and regulation. Growth of the dguR and dguA mutants was abolished completely on d-Glu or retarded on d-Gln as the sole source of carbon and/or nitrogen. The dguA gene encoded a FAD-dependent d-amino acid dehydrogenase with d-Glu as its preferred substrate, and its promoter was specifically induced by exogenous d-Glu and d-Gln. The function of DguR as a transcriptional activator of the dguABC operon was demonstrated by promoter activity measurements in vivo and by mobility shift assays with purified His-tagged DguR in vitro. Although the DNA-binding activity of DguR did not require d-Glu, the presence of d-Glu, but not d-Gln, in the binding reaction was found to stabilize a preferred nucleoprotein complex. The presence of a putative DguR operator was revealed by in silica analysis of the dguR–dguA intergenic regions among Pseudomonas spp. and binding of DguR to a highly conserved 19 bp sequence motif was further demonstrated. The dguB gene encodes a putative enamine/imine deaminase of the RidA family, but its role in d-Glu catabolism remains to be determined. Whilst a lesion in dguC encoding a periplasmic solute binding protein only affected growth on d-Glu slightly, expression of the previously characterized AatJMQP transporter for acidic l-amino acid uptake was found inducible by d-Glu and essential for d-Glu utilization. In summary, the findings of this study supported DguA as a new member of the FAD-dependent d-amino acid dehydrogenase family, and DguR as a d-Glu sensor and transcriptional activator of the dguA promoter.
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Funding
- National Science Foundation (Award NSF0950217)