, 2007). This notion led us to predict an important role for H 89 concentration any lipolytic enzyme of P. aeruginosa, which, like EstA, may have access to lipids of the bacterial outer membrane. Therefore, we have analysed the physiological role of the newly described lipase LipC, which also exerted significant effects on cellular motility as well as on the production of rhamnolipids. Accordingly,

biofilms formed by the lipC mutant showed a significantly different architecture than the corresponding wild-type biofilms. Rhamnolipids are detergent-like sugarlipids that may act as ‘wetting’ agents and also play a role as virulence factors (Daniels et al., 2004; Zulianello et al., 2006). The rhamnolipid biosynthesis pathway includes two sequential rhamnosyl transferase reactions (Rahim et al., 2001) starting from HHAs as precursors (Deziel et al., 2003), which are also present in culture supernatants and possess detergent-like properties (Deziel

et al., 2003). Recent studies have shown that HAAs as well as di-rhamnolipids can act as antagonizing stimuli on swarming motility (Tremblay et al., 2007). Rhamnolipids also play multiple roles in the maturation of biofilms because they promote motility and the maintenance of water-filled channels (Davey et al., 2003). Recently, experimental evidence was presented Tanespimycin solubility dmso indicating that twitching motility also requires rhamnolipid production. In the lipC mutant, swimming was also affected, whereas an rhlA mutant

did not show any difference as compared with the wild-type strain (data not shown). This result clearly indicates that the reduction in rhamnolipid DNA ligase production itself cannot explain the pleiotropic phenotype of the lipC mutant. Recently, Hancock’s lab has performed a comprehensive study on swarming motility of P. aeruginossa. They found that transposon insertion into a gene encoding the pseudopilus protein XcpU required for type II secretion resulted in decreased swarming motility and biofilm formation. However, it remained unclear whether XcpU itself exerted the observed effects or other secreted factors were also involved (Overhage et al., 2007). The swarming defect we have observed for the lipC mutant indeed indicates the requirement of additional extracellular enzymes as LipC has been shown to be secreted by the Xcp machinery (Martinez et al., 1999). Furthermore, two secreted lipolytic enzymes also interfere with motility in P. aeruginosa: (1) the autotransporter EstA located in the outer membrane is required for all types of motility and the formation of the typical architecture of wild-type biofilms and (2) the extracellular phospholipase PlcB is involved in twitching motility along phospholipid gradients (Barker et al., 2004), but its influence on swimming, swarming and biofilm formation is unknown.