Arginine can serve many bacteria as a source of carbon, energy, and nitrogen, as a building unit of proteins, and as a precursor of polyamine synthesis14, 27. It can also be an ammonia source for bacterial adaptation to acid environments13, 59, 101. All of the major arginine catabolic pathways initiated by arginase, arginine deiminase (ADI), arginine succinyltransferase (AST), arginine decarboxylase (ADC), or arginine dehydrogenase (ADH), occur in bacteria14. Many bacteria have more than one route to utilize arginine depending on the physiological purpose. Pseudomonas aeruginosa PAO1 possesses four pathways of arginine metabolism (ADI, AST, ADC and ADH; Figure 1). The ADI and AST pathway genes were first established in strain PAO128, 39. Several ADC and ADH pathway genes have been recently identified and characterized in this strain65, 68.