Positive regulation of amidase synthesis in Pseudomonas aeruginosa

Abstract

Mutants of P. aeruginosa were isolated that were acetamide-negative in growth phenotype at 41°C and constitutive for amidase synthesis at 28°C. Two mutants were derived from the magno-constitutive amidase mutant PAC111 (C11), and a third from a mutant that had enhanced inducibility by formamide, PAC153 (F6). The three temperature-sensitive mutants produced amidases with the same thermal stabilities as the wild-type enzyme. Cultures growing exponentially at 28°C, synthesizing amidase constitutively, ceased amidase synthesis almost immediately on transfer to 41°C. Cultures growing at 41°C were transferred to 28°C and had a lag of about 0.5 of a generation before amidase synthesis became detectable. Pulse-heating for 10 min at 45°C of a culture growing exponentially at 28°C resulted in a lag of about 0.5 of a generation before amidase synthesis recommenced after returning to 28°C. Acetamide-negative mutants that were unable to synthesize amidase at any growth temperature were isolated from an inducible strain producing the mutant B amidase PAC398 (IB10). Two mutants were examined that gave revertants producing B amidase but with novel regulatory phenotypes. It is suggested that amidase synthesis is regulated by positive control exerted by gene amiR.