Purum p a

For the experiments with restricted contact between bacterial cells and elemental sulfur, solid sulfur (purum p.a. > 99.5%, Sigma-Aldrich) was embedded in alginate beads. The technique of preparation of alginate beads was adopted from Gavrilov et al., 2012 (link). A freshly prepared suspension of sulfur in distilled water (100 g l^-1) was slowly added to 1.5% (w/v) solution of sodium alginate under intense stirring. The suspension was left for 30 min to eliminate air bubbles, then gently stirred for an hour and subsequently manually dripped through a micropipette tip into a solution of 33 g l^-1 CaCl₂ from a height of ca. 10 cm. The beads formed were of 2.0–2.5 mm diameter and were left in CaCl₂ solution overnight to cure, then separated from the solution and washed on a vacuum filter with distilled water. Wet beads were dispensed into Hungate tubes to the bulk volume of ca. 1.5 ml. After adding the beads, the tubes were filled with liquid freshly prepared medium of the same composition as used in growth experiments to the total volume of 10 ml under CO₂ efflux. The obtained medium contained ca. 150 mmol l^-1 of elemental sulfur entrapped in alginate. The medium was sterilized by autoclaving at 105°C.

For the preparation of samples, o-phthaldialdehyde (≥97% for HPLC), 2-mercaptoethanol (≥99.0%), potassium bromide (Purum p.a., ≥99.5%) and boron trifluoride BF3 (10–20% in methanol) were from Sigma-Aldrich (Saint-Quentin Fallavier, France). Purified water (18 MΩ cm) was produced in-house from an Academic MilliQ model water purification unit (Millipore, EMD Millipore Corporation, Billerica, MA, USA). For the preparation of LC mobile phases, acetonitrile (RS for isocratic HPLC, Carlo-Erba Reagents, Val-de-Reuil, France) and methanol (Lichrosolv for HPLC, Merck, Darmstadt, Germany) were used. All other solvents and reagents were of analytical grade.
The mycotoxin primary standard solution of OTA (10 µg/mL in acetonitrile) was from Sigma-Aldrich Chemie (Schnelldorf, Germany). FB1 and FB2 together (50 µg/mL each in an acetonitrile–water mixture) were from Romer labs (Getzersdorf, Austria). Aflatoxins B1, B2, G1 and G2 (250 ng/mL of each in acetonitrile) were purchased from Libios (Bully, France) and T-2 Toxin (100 µg/mL in acetonitrile), HT-2 Toxin (100 µg/mL in acetonitrile), DON (100 µg/mL in methanol) and ZEA (25 µg/mL in methanol) were procured from R-Biopharm (Saint-Didier-au-Mont-d’Or, France).