RESUMEN
The acidic amino acids (Asp, Glu) and their amides (Asn, Gln) are excellent growth substrates for many pseudomonads. This paper presents proteomics data indicating that growth of Pseudomonas fluorescens ATCC 13525 and Pseudomonas putida KT2440 on these amino acids as sole source of carbon and nitrogen leads to the induction of a defined set of proteins. Using mass spectrometry and N-terminal sequencing, a number of these proteins were identified as enzymes and transporters involved in amino acid uptake and metabolism. Most of them depended on the alternative sigma factor sigma(54) for expression and were subject to strong carbon catabolite repression by glucose and citrate cycle intermediates. For a subset of the identified proteins, the observed regulatory effects were independently confirmed by RT-PCR. The authors propose that the respective genes (together with others still to be identified) make up a regulon that mediates uptake and utilization of the abovementioned amino acids.
Asunto(s)
Asparagina/farmacología , Ácido Aspártico/farmacología , Proteínas Bacterianas/biosíntesis , Ácido Glutámico/farmacología , Glutamina/farmacología , Pseudomonas fluorescens/metabolismo , Pseudomonas putida/metabolismo , Asparaginasa/biosíntesis , Glutaminasa/biosíntesis , Periplasma/enzimología , Proteómica , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Factor sigma/fisiologíaRESUMEN
The acidic amino acids (Asp, Glu) and their amides (Asn, Gln) support rapid growth of a variety of Pseudomonas strains when provided as the sole source of carbon and nitrogen. All key enzymes of glutamate metabolism were detected in P. fluorescence, with glutaminase and asparaginase showing the highest specific activities. A periplasmic glutaminase/asparaginase activity (PGA) was found in all pseudomonads examined, including a number of root-colonizing biocontrol strains. The enzyme was purified and shown to be identical with the ansB gene product described previously. In addition to PGA, P. fluorescens contains a cytoplasmic asparaginase with marked specificity for Asn. PGA is strongly and specifically induced by its substrates (Asn, Gln) but also by the reaction products (Asp, Glu). In addition, PGA is subject to efficient carbon catabolite repression by glucose and by citrate cycle metabolites. A mutant of P. putida KT2440 with a disrupted ansB gene was unable to utilize Gln, whereas growth of the mutant on other amino acids was normal.