5 min respectively and was ended by one step of 72°C for 5 min. The amplified fragment was cleaned

using the Qiagen PCR purification kit (Qiagen Benelux B.V.) and restricted with BamHI and EcoRI. This restricted epsC gene fragment was ligated into BamHI-EcoRI restricted pGEX-6p-3 plasmid to yield pGEX-PG0120. The 1.2 Kb EryF erythromycin resistance cassettes for use in P. gingivalis was amplified from plasmid pEP4351 using primers EryF ClaI F and EryF ClaI R. and after restriction with ClaI this fragment was ligated into the ClaI-restricted pGEX-PG0120 plasmid yielding pΔEpsC. The ScaI-linearized Geneticin mw pΔEpsC plasmid was used for insertional inactivation of epsC in P. gingivalis strain W83. Complementation of the epsC mutant The 120 bp artificial constitutive CP25 promoter [37] was amplified from plasmid pDM15 [38] using primers CP25 ClaI F and CP25 AscI R. The intact epsC 1.2 Kb gene was amplified from genomic DNA of P. gingivalis strain W83 using primers epsC AscI F and epsC SpeI R. After ligation of these fragments into cloning vector pJET1.2 (Fermentas, GmbH, St. Leon-Rot, Germany) the constructed expression cassette was cut out with XhoI and HindIII and ligated into the selleck screening library SalI and HindIII digested pT-COW shuttle plasmid [39] to yield the complementation construct pT-PG0120. Transformation of P. gingivalis BHI+H/M was inoculated

with P. gingivalis W83 from a 6-day-old blood agar plate. This pre-culture was anaerobically incubated at 37°C for 2 days. 2 ml of the pre-culture was used to inoculate a 100 ml culture. The next day this culture was used to inoculate 2 × 100 ml of fresh

BHI+H/M to an OD690 of 0.2. After six hours of anaerobic incubation at 37°C the cells were harvested by centrifugation in mid-exponential phase. The pellet was washed two times in 20 ml EPB (10% glycerol, 1 mM MgCl2) and after that resuspended in 2 ml of EPB. Aliquots of 200 μl were stored at -80°C and used for electroporation. 200 ng of PstI digested pΔEpsC was added to 200 μl of W83 P. gingivalis cells. The mixture was transferred to a 2 mm electroporation cuvette and electroporated using an Electro Cell Manipulator Parvulin 600 (BTX Instrument Division, MAPK inhibitor Holliston, MA, USA; 25 μF, 2.5 kV, 186 Ω). 1 ml of BHI+H/M was added immediately after the pulse. The cells were left for recovery anaerobically at 37°C for 18 hours. The suspension was plated on BA+H/M plates with 5 μg/ml erythromycin for selection of the transformants. The authenticity of the insertional knockout epsC mutants was verified using primer combinations epsC BamHI F × PG0119 R and EryF ClaI F × epsC EcoRI R. Furthermore, using Real-Time PCR, the expression of the downstream gene hup-1 in both W83 and the epsC mutant was monitored using primers hup-1 F and hup-1 R to exclude polar effects. W83 and the epsC mutant were grown till early exponential phase. The cell pellets were collected by centrifugation and resuspended in RLT buffer (Qiagen, Benelux B. V.