Identification of a Novel Caspase-3-Like Protease, Clp, in Pseudomonas aeruginosa Biofilms and its Modulation of Rapid Cell Death

Abstract

Pseudomonas aeruginosa, a major cause of nosocomial infections, is able to evade the host immune response and confer antibiotic resistance by undergoing the dynamic process of biofilm formation. It has previously been shown that autolysis or rapid cell death (RCD) may be an important part of biofilm survival during conditions of nutrient limitation by releasing nutrients and forming channels for improved nutrient flow. Details of RCD in Pseudomonas have not been elucidated but evidence suggests that expression of caspaselike proteins and other proteases may be involved. Here, we have demonstrated the inducible expression of caspase-3-like proteins upon biofilm formation. Using the mini- Tn 5 – luxCDABE fusion PAO1 library, we have specifically identified Clp, a caspase-3-like protein with homology to the Lon protease of Pseudomonas and LonB in Escherichia coli, to be required for motility-independent structured biofilm formation. Our data suggest that Clp may be involved in a proteolytic cascade leading to RCD in nutrient limited growth of P. aeruginosa.