L-Lysine Catabolism Is Controlled by L-Arginine and ArgR in

In comparison to other pseudomonads, Pseudomonas aeruginosa grows poorly in L-lysine as a sole source of nutrient. In this study, the ldcA gene (lysine decarboxylase A; PA1818), previously identified as a member of the ArgR regulon of L-arginine metabolism, was found essential for L-lysine catabolism in this organism. LdcA was purified to homogeneity from a recombinant strain of Escherichia coli, and the results of enzyme characterization revealed that this pyridoxal-5-phosphate-dependent decarboxylase takes L-lysine, but not L-arginine, as a substrate. At an optimal pH of 8.5, cooperative substrate activation by L-lysine was depicted from kinetics studies, with calculated Km and Vmax values of 0.73 mM and 2.2 mole/mg/min, respectively. Contrarily, the ldcA promoter was induced by exogenous L-arginine but not by L-lysine in the wild-type strain PAO1, and the binding of ArgR to this promoter region was demonstrated by electromobility shift assays. This peculiar arginine control on lysine utili-zation was also noted from uptake experiments in which incorporation of radioactively labeled L-lysine was enhanced in cells grown in the presence of L-arginine but not L-lysine. Rapid growth on L-lysine was detected in a mutant devoid of the main arginine catabolic pathway and with a higher basal level of the intracellular L-arginine pool and hence elevated ArgR-responsive regulons, including ldcA. Growth on L-lysine as a nitrogen source can also be enhanced when the aruH gene encoding an arginine/lysine:pyruvate transaminase was expressed constitutively from plasmids; however, no growth of the ldcA mutant on L-lysine suggests a minor role of this transaminase i