REGULATION OF ORNITHINE UTILIZATION IN PSEUDOMONAS-AERUGINOSA (PAO1) IS MEDIATED BY A TRANSCRIPTIONAL REGULATOR, ORUR

We have used transpositional mutagenesis of a proline auxotroph (PAO95 1) to isolate an ornithine utilization (one) mutant of Pseudomonas aer uginosa (PAO951-4) that was unable to use ornithine efficiently as the sole carbon End nitrogen source. DNA sequence analysis of the inactiv ated locus confirmed that the transposon had inserted into a locus who se product demonstrated significant primary sequence homology to membe rs of the AraC family of transcriptional activators. DNA mobility shif t assays affirmed this potential regulatory function and indicated tha t the inactivated gene encodes a transcriptional regulator, which has been designated OruR. In trying to define the ornithine utilization ph enotype further, a similar inactivation was engineered in the wild-typ e strain, PAO1. The resulting isolate (PAO1R4) was totally unable to u se ornithine as the sole carbon source. Despite the intensified phenot ype, this isolate failed to demonstrate significant changes in any of the catabolic or anabolic enzymes that are known to be subject to regu lation by the presence of either ornithine or arginine. It did, howeve r, show modified levels of an enzyme, ornithine acetyltransferase (OAc T), that was previously thought to have merely an anaplerotic activity . Definition of this oruR locus and its effects upon OAcT activity pro vide evidence that control of ornithine levels in P. aeruginosa may ha ve a significant impact upon how the cell is able to monitor and regul ate the use of arginine and glutamate as sources of either carbon or n itrogen.