Protein precipitate was collected by centrifugation at 10,000 × g (2°C, 30 min). Membrane proteins were extracted by resuspending cell pellets in sodium carbonate (0.1 M, pH 11) and stirred on ice for 1 h. The carbonate-treated membranes were collected by ultra-centrifugation (115,000 × g, 4°C, 1 h). Extracted buy GS-7977 cytoplasmic and membrane proteins were then solubilised with ReadyPrep Reagent

3 (Bio-Rad Laboratories, CA, USA) containing 5 M urea, 2 M thiourea, 2% (w/v) CHAPS, 2% (w/v) detergent sulfobetaine 3–10, 40 mM Tris, 0.2% Bio-lyte 3/10 and 2 mM tributyl selleck compound phosphine and stored at −80°C until required. Protein separation by two-dimensional gel electrophoresis (2DE) Protein quantification was performed using Reducing Agent and Detergent Compatible Protein Assay Kit (Bio-Rad Laboratories, CA, USA) prior to 2DE. Gel-based isoelectric focusing (IEF) was performed using a PROTEAN IEF Cell (Bio-Rad Laboratories, CA, USA) using pre-cast Immobilised pH Gradient (IPG) strips with an isoelectric point (pI) range of 4–7 or 7–10 and proteins were cup-loaded onto the anode end of IPG strips. Optimal protein load and IEF running conditions are listed

in Additional file 1: Table S1. Cytoplasmic selleck screening library proteins with a pI between 7 and 10 required an additional liquid-based IEF separation prior to 2DE. A total of 10 mg of solubilised cytoplasmic proteins were separated into 10 fractions between pI 3 and 10 using a MicroRotofor Liquid-Phase IEF Cell (Bio-Rad Laboratories, CA, USA). Liquid-based IEF was performed at 20°C at 1 W for 2 h. The fractions between pI 7 and 10 were pooled and following

protein determination, separated by 2DE. Following 2DE IEF, IPG strips were incubated in 2% (w/v) DTT in equilibration buffer (6 M urea, 2% (w/v) SDS, 0.05 M Tris/HCl buffer (pH 8.8) and 20% (v/v) glycerol), followed by 2.5% (w/v) iodoacetamide in equilibration buffer for 15 min each. Proteins were then separated on 20 × 20 cm polyacrylamide Bumetanide (12% T, 3.3% C, 0.1% SDS, 375 mM Tris/HCl, pH 8.8) gels using a PROTEAN II XL Multi-Cell (Bio-Rad Laboratories, CA, USA) which allowed six gels to be run simultaneously. Gels were stained with either Coomassie Brilliant Blue R-250 (Sigma Aldrich, MO, USA) or Flamingo Fluorescent Stain (Bio-Rad Laboratories, CA, USA) and scanned using a GS-800 Densitometer (Bio-Rad Laboratories, CA, USA) or Typhoon Scanner (GE Healthcare, Buckinghamshire, UK), respectively. Image acquisition and analysis Image analysis of the 2-DE gels was performed using PD-Quest 7.2 Software (Bio-Rad Laboratories, CA, USA). Six gels were produced for each pI range (4–7 and 7–10) for cytoplasmic and cell membrane proteins from either biofilm or planktonic cells (48 gels in total). Replicate groups containing four to six highly reproducible gels from either planktonic or biofilm cells were used for analysis. Spot intensities were normalised using the total density in gels.