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Mutants isolated from Pseudomonas aeruginosa strain PAO1632 (Hut−Ami−) were unable to utilize l-arginine or l-ornithine as the carbon source for growth. Arginine deiminase (AD), catabolic ornithine carbamoyltransferase (cOTC) and N 2-acetylornithine 5-aminotrans-ferase (ACOAT) were present in the mutants but these enzymes were not induced to higher levels by exogenous l-arginine. One group of mutants could utilize l-ornithine but not l-arginine and in these strains l-arginine induced the synthesis of ACOAT but not AD or cOTC. The mutations of the arginine utilization-negative mutants were all in genes of the same transductional linkage group and mapped in the 45 to 50 min region of the chromosome. Revertants isolated on l-arginine or l-ornithine plates were derepressed for the synthesis of ACOAT. It is suggested that l-arginine is normally catabolized by the wild-type strain via the arginine deiminase pathway and requires a threshold level of ACOAT. The regulatory factors controlling the functioning of the divergent arginine deiminase and arginine carboxylase pathways are discussed.
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