Methyl 10 undecenoate

The bacterial cell fatty acid composition was determined by GC/MS as described [25 (link)]. S. sanguinis cells were harvested from overnight cultures in BM medium under anaerobic conditions by centrifugation and washed twice with dH₂O. The cell pellets were mixed with 0.5 ml 1 N sodium methoxide for 1 min and the fatty acid methyl esters were extracted by addition of 0.3 ml hexane containing methyl-10-undecenoate (Sigma-Aldrich, St. Louis, MO) as an internal standard. GC/MS analysis was carried out on Varian Saturn GC/MS (VCU core facilities) equipped with a Restek Stabilwax-DA column (30 m × 0.25 mm × 0.5 μm). Carried gas (H₂) velocity was 1 ml/min. Injection and detection temperature were 230 °C and 260°C, respectively. The oven temperature was increased from 100°C to 240°C at 5°C/min and maintained for 20 min. The peaks with their retention times were identified by MS. Each fatty acid composition was expressed as percentage of the total content of fatty acids.

Whole cell esterified fatty acid determinations were done essentially as described62 (link). Briefly, 1–2 ml S. aureus cultures (OD₆₀₀=≥1) were centrifuged, washed once in 0.9% NaCl containing 0.02% Triton X-100, then washed twice in 0.9% NaCl. Cell pellets were treated with 0.5 ml of 1 N sodium methoxide. Heptane (200 μl) was then added, together with methyl-10-undecenoate (Sigma-Aldrich) as internal standard, vortexed for 1 min, and centrifuged. Fatty acid methyl esters were recovered in the heptane phase. Analyses were performed in a split-splitless injection mode on an AutoSystem XL Gas Chromatograph (Perkin-Elmer) equipped with a ZB-Wax capillary column (30 m × 0.25 mm × 0.25 μm; Phenomenex, France). Data were recorded and analysed by TotalChrom Workstation (Perkin-Elmer). S. aureus fatty acid peaks were detected between 12 and 30 min of elution.

Ultra-high-purified water and methylene chloride HPLC grade, methyl 10-undecenoate, anhydrous sodium sulfate, and sodium chloride were purchased from Sigma-Aldrich (Steinheim, Germany). Ultra-high-purified methylene chloride HPLC grade from Merck (Darmstadt, Germany) was used as the solvent for extraction.