Alteration of the lipopolysaccharide structure affects the functioning of the Xcp secretory system in Pseudomonas aeruginosa

Pseudomonas aeruginosa secretes a wide range of hydrolytic enzymes into the external medium by the Xcp secretion machinery. To better understand the r ole played by envelope constituents in the functioning of this type II secr etory system, we have studied the influence of lipopolysaccharide (LPS) on the secretion of two extracellular enzymes, the elastase LasB and the lipas e LipA. Strains with defective LPS decreased production of LasB and altered the secretion processes of both LasB and LipA without any apparent effect on the composition of the Xcp machinery. The PAO1algC strain, defective in the outer core of LPS, was leaky, as shown by the extracellular release of the periplasmic P-lactamase. Generation of an xcpR mutation in this mutant led only to a partial accumulation of LasB within the cells, indicating tha t in strain PAO1algC with a functional xcpR gene, LasB was released in the extracellular medium partly by leakage and partly by secretion. The pool of LasB released into the medium by leakage was not recovered in an active fo rm, while extracellular LasB was active when secreted via the secretory mac hinery. Further analysis revealed that the presence of a functional Xcp mac hinery is strictly required for the activation process of LasB. Our results provide evidence that the Xcp system is not fully functional when the LPS structure of P. aeruginosa is altered.