The expression of PA2783 throughout the growth cycle of P. aeruginosa follows a unique pattern. PA2783 codes for a secreted metalloendopeptidase, which we named Mep72. Mep72, which has metalloendopeptidase and carbohydrate-binding domains, produced proteolytic and endopeptidase activities in E. coli. Vfr directly regulates the expression of the PA2782-mep72 operon by binding to its upstream region. However, unlike other Vfr-targeted genes, Vfr 4EGI-1 order binding does not require an intact Vfr consensus binding sequence. Methods Strains, plasmids, and general growth conditions Bacterial strains and plasmids used in this study are listed in Table 1. For routine growth, strains were grown in Luria-Bertani

(LB) broth [29]. Antibiotics were used at the following concentrations as appropriate: for E. coli, 100 μg carbenicillin/ml and/or 50 μg kanamycin/ml; for P. aeruginosa, 300 μg carbenicillin/ml, 60 μg gentamicin/ml, 300 μg kanamycin/ml, or 50 μg tetracycline/ml. General DNA techniques Plasmid DNA extraction

was performed using the Wizard Plus MiniPreps DNA Purification system and genomic DNA was extracted from PAO using the Wizard Genomic DNA Purification PI3K Inhibitor Library manufacturer kit (Promega, Madison, WI). Daporinad restriction digestion, ligation and transformation of E. coli were done as described [56]. Plasmids were introduced into P. aeruginosa by electroporation [57]. Construction of cloning and expression plasmids An 1807-bp PAO1 chromosomal fragment containing the PA2783 ORF Flucloronide was amplified by PCR using primers PA2783orf-F/PA2783orf-R (see Additional file 1). The PCR product was cloned

into pCR2.1-TOPO (Invitrogen, Carlsbad, CA) generating plasmid pAB1. An 1827-bp fragment carrying PA2783 was excised from the pAB1 plasmid by EcoRI digestion and ligated into the EcoRI site of the E. coli-Pseudomonas shuttle vector pUCP19 to generate plasmid pAB2. Overexpression of PA2783 to produce rPA2783 (rMep72) was done as follows: the 1827-bp EcoRI fragment carrying PA2783 was excised from pAB1 and ligated into the pBAD/HisC expression vector (Invitrogen) to produce the plasmid pAB4. Construction of plasmids was confirmed by restriction digestion. Quantitative reverse transcriptase PCR (qRT-PCR) and RT-PCR Overnight cultures of P. aeruginosa strains PAO1 and PAO1∆vfr were subcultured in LB broth to an OD600 of 0.02 and grown for up to 6 h at 37°C. Cultures were harvested at early log phase of growth (OD600 0.37-0.41) and mid log phase (OD600 0.79-0.89). Cultures were mixed with twice the volume of RNAprotect Bacteria Reagent (QIAGEN, Valencia, CA) for 5 min at room temperature and the cells were pelleted. Pelleted cells were lysed using lysozyme and proteinase K for 15 min at room temperature, and then the total RNA was extracted using the RNeasy Mini Kit (QIAGEN) according to the manufacturer’s instructions. To remove genomic DNA, the RNA solution was treated with the RNase-free DNase Set (QIAGEN).