aeruginosa SG81ΔlipA, the corresponding complementation strain P. aeruginosa SG81ΔlipA::lipA and the lipA overexpression strain P. aeruginosa SG81lipA + carrying plasmid pBBL7 were used. This vector based on pBBR1MCS [64] and carries the genes lipA and lipH from P. aeruginosa PAO1 [1]. For construction of a ΔlipASAHA molecular weight -mutant from SG81 a Gmr cassette was cloned into the suicide vector pMEΔAH11 [63] containing a 2.06 kbp KpnI/XbaI-fragment

with Δ(2/3 lipA 1/5 lipH). The resulting vector pMEΔAH::Ω-Gmr was used for homologous recombination. QNZ All plasmids were transferred into P. aeruginosa SG81 via conjungation using Escherichia coli S-17. Table 3 Bacterial strains and plasmids used in this study Strain/plasmids Relevant genotype/ phenotype Reference E. coli S17-1 thi pro hsdR – M +, chromosomally integrated [RP4-2 Tc::Mu:Kmr::Tn7, Tra+ Trir Strr] [65] P. aeruginosa   [38] PABST7.1/pUCPL6A Overexpression of lipA and lipH from pUCPL6A FRD1 Mucoid ΔmucA22 CF-lung isolate [66] FRD1153 ΔalgJ5-mutant derived from FRD1, defect in O-acetylation of alginate [61, 62] SG81 Mucoid biofilm isolate from technical water system [67] SG81MCS Vector control pBBR1MCS [1] SG81ΔlipA Δ(2/3 lipA 1/5 lipH)::Ω-Gmr

, deletion of lipA and lipH This study SG81ΔlipA::lipA Deletion of lipA and lipH complemented in trans from pBBL7 This study SG81lipA+ Expression of lipA and lipH in trans from pBBL7 [1] pBBR1MCS lacZα Cmr mob Plac, PT7 [64] pBBL7 2.8 kbp XmnI/SmaI fragment with lipA/H operon in pBBR1MCS under Plac control   pMEΔAH11 2.06 kbp KpnI/XbaI-fragment with

Δ(2/3 see more lipA 1/5 lipH) in pME3087 [63] pMEΔAH::Ω-Gmr 1.6 kbp SmaI-fragment with Ω-Gmr from pBSL142 in pMEΔAH11 This study Biofilm Silibinin cultures were grown for 24 h at 36°C on Pseudomonas Isolation Agar (PIA; Difco) in the form of confluent mucoid lawns. Cell numbers of biofilms, which were scraped from the agar surface and suspended in 0.14 M NaCl, were determined microscopically using a Thoma counting chamber. Cell-free EPS solutions prepared from the biofilm suspensions according to Tielen et al. [1] were used to measure uronic acid (alginate) concentration and lipase activity as described below. For CLSM analysis, biofilms were grown on membrane-filters (polycarbonate, size: 2.5 cm, pore size: 0.4 μm; Millipore, Billerica, Massachusetts) placed on PIA supplemented with 0.1 M CaCl2 for stabilization of the biofilm matrix as described previously [68]. Visualization of lipase activity in situ For visualization of lipase activity in biofilms of P. aeruginosa strains, ELF® 97 palmitate (Molecular Probes, Invitrogen GmbH, Karlsruhe, Germany) was used as a substrate. This enzyme substrate is cleaved by lipases to the water-insoluble ELF® 97 alcohol, which precipitates directly at the site of enzymatic hydrolysis, thus reporting the location of lipase enzyme activity, when visualized by fluorescence microscopy [69].