A tube section was excised and cut lengthwise into two pieces. The bottom part, where the cells settle and form the biofilm, was immersed PLX4032 order overnight in fixing buffer (1% paraformaldehyde, 2.5% gluteraldehyde in 0.1 M sodium cacodylate buffer, pH 7.2–7.4). The fixed samples were rinsed twice for 10 min in 0.1 M sodium cacodylate buffer and dehydrated twice for 5 min in 50%, 70%, 90% and 100% ethanol solutions. Samples were dried at room temperature. Samples were coated with a thin film of iridium, 15 s at 20 mA, in a Emitech sputter coater. Cells were viewed

with a Supra 55VP FESEM (Zeiss) using the Inlens detector at 1 kV and 3 mm working distance. RNA preparation Biofilm samples were collected by first clamping and then removing the colonized section of the tubing. The liquid column was drained

into a 50 ml polypropylene tube placed in an ice bath by moving the tubing to a vertical position and releasing the clamps. For 1 h biofilms the more firmly attached biofilm was then removed by rolling the tubing between the hands followed by flushing the tube with 25 ml of ice-cold RNase-free water using a 50 ml syringe to achieve the highest pressure possible. This procedure was accomplished in less than 3 min for each experiment. Cells from batch cultures were collected by pouring the contents of the culture flask into 50 ml polypropylene tubes this website in an ice bath. Cells from biofilm or batch cultures were centrifuged at 4°C in 10–20 ml aliquots at 2500 × g for 3 min, washed with ice-cold RNase-free H2O and immediately flash-frozen in liquid N2 and stored at -80°C until use. To release the RNA from cells, samples stored at -80°C were placed on ice and RNeasy buffer RLT was added to pellets at a ratio of 10:1 [vol/vol] buffer/pellet. The pellet was allowed to thaw in the buffer while vortexing briefly at high speed. The resuspended pellet was placed back on ice and divided into 1 ml aliquots in 2 ml screw cap microcentrifuge tubes containing 0.6 ml of 3 mm diameter acid-washed glass beads. Samples were homogenized

5 times, 1 min each, at 4200 RPM using the Mini-Beadbeater mill (Biospec Parvulin Products Inc., Bartlesvile, OK, USA). Samples were placed on ice for 1 min after each homogenization step. After the homogenization the Qiagen RNeasy protocol was followed as recommended. Total RNA samples were eluted in RNase free H2O, flash-frozen in liquid N2, lyophilized and stored at -80°C until used for the different analyses. Microarray experiments: cDNA labeling, hybridizations and data analysis Four independent biological replicates were performed for each hybridization comparison. Labeling of the four biological replicate was performed using a dye-swap strategy that resulted in 2 experiments with Cy3/Cy5 and two experiments Cy5/Cy3 ratios. RNA quality and integrity were assessed using an Agilent 2100 Bioanalyzer.