4.14. Analytical scale culture extraction and HPLC-UV/MS analysis

P. luminescens strains were inoculated in LB media in 100 ml Erlenmeyer flasks with an overnight culture to an OD₆₀₀ of 0.1 and aerobically grown for 24 h at 30 °C. For ethyl acetate (EE) extractions 2 ml samples of the cultures were extracted for 1 h at RT with 2 ml EE + 0.1% FA. 1 ml of the organic supernatant was dried under nitrogen flow. The extracts were re-dissolved in 250 μl methanol and measured by HPLC-UV/MS. HPLC-UV/MS analysis was done as explained before [50]. We used an ACN/0.1% FA in H₂O/0.1% FA gradient from 5 to 95% in 12 min at a flow rate of 0.6 ml/min at 30 °C. Chromatograms were analyzed using Bruker Compass DataAnalysis 4.2. For AQ quantification peak areas of the HPLC-UV analysis (UV-chromatograms at 430 nm) were used. For SM quantification, peak areas of the HPLC-MS chromatogram were determined using Bruker Compass TargetAnalysis Version 1.3. The respective peak areas were normalized against the cell density (OD₆₀₀) when cultures were harvested.