Surfactin quantification

Surfactin was only measured from the cultivation broth. Therefore, surfactin produced was quantified using high-performance thin-layer chromatography (HPTLC) (CAMAG AG, Muttenz, Switzerland). All experimental details were described by Geissler et al. [22]. In brief, 2 mL of the cell-free supernatant was used for a threefold extraction with chloroform/methanol (2:1). The pooled solvent layers were dried using a rotary evaporator (RVC 2–25 Cdplus, Martin Christ Gefriertrocknungsanlagen GmbH, Osterode am Harz, Germany) at 40 °C and 10 mbar. After dissolving in 2 mL methanol, the samples were applied in 6-mm bands to a silica HPTLC plate. Migration at a distance of 60 mm was performed with a mixture of chloroform/methanol/water (65:25:4) as mobile phase before surfactin detection at 195 nm [22]. A surfactin standard (Sigma Aldrich, Seelze, Germany) was used for quantification.