Secretion of toxin A from Pseudomonas aeruginosa PAO1, PAK, and PA103 by Escherichia coli.

The exotoxin A gene (toxA) from Pseudomonas aeruginosa PAO1 was expressed from the lac promoter in Escherichia coli, and the localization of the toxin A protein was determined. Throughout the growth cycle, the ADP-ribosyltransferase activity of toxin A was gradually reduced in the periplasm of E. coli, with no apparent degradation of the toxin A protein. This suggests the presence of an E. coli periplasmic factor that interferes with the ADP-ribosyltransferase activity in toxin A. Such an inactivating factor was found in the periplasmic extract from control E. coli cells. The processing of toxin A in E. coli was examined by pulse-chase immunoprecipitation experiments. Mature toxin was detected in both the periplasm and cytoplasm, whereas the membranes contained both mature and precursor forms. Toxin A precursor appears to be processed in both the cytoplasm and the periplasm of E. coli. Toxin A proteins from P. aeruginosa PAO1, PA103, and PAK were compared for their secretion in E. coli. Despite the differences in the amino acid sequences of their leader peptides, toxin A proteins from strains PAO1, PA103, and PAK were processed and secreted to the periplasm of E. coli.