A novel type II secretion system in Pseudomonas aeruginosa

The genome sequence of Pseudomonas aeruginosa strain PAO1 has been determined to facilitate postgenomic studies aimed at understanding the capacity of adaptation of this ubiquitous opportunistic pathogen. P. aeruginosa produces toxins and hydrolytic enzymes that are secreted via the type II secretory pathway using the Xcp machinery or 'secreton'. In this study, we characterized a novel gene cluster, called hxc for homologous to xcp. Characterization of an hxcR mutant, grown in phosphate-limiting medium, revealed the absence of a 40 kDa protein found in the culture supernatant of wild-type or xcp derivative mutant strains. The protein corresponded to the alkaline phosphatase L-AP, renamed LapA, which is secreted in an xcp-independent but hxc-dependent manner. Finally, we showed that expression of the hxc gene cluster is under phosphate regulation. This is the first report of the existence of two functional type II secretory pathways within the same organism, which could be related to the high adaptation potential of P. aeruginosa.