Sodium methanethiolate

To study MeSH degradation and DMS produced through the Mdd pathway, 1 g of saltmarsh sediment from each of the three biological samples was placed in a 125 ml sealed vial containing 20 ml distilled water 35 PSU, 5 % Marine Basal Medium (MBM; Baumann and Baumann, 1981 ), 10 mM mixed carbon source (C; 200 mM succinate, 200 mM glucose, 200 mM sucrose, 200 mM pyruvate, 200 mM glycerol) and 20 μmol MeSH added as sodium methanethiolate (Sigma-Aldrich). Additions of sodium methanethiolate are cited in text as additions of MeSH. Microcosm experiments were incubated at 22°C for 24 h before measuring headspace MeSH and DMS concentration by gas chromatography (GC) as detailed in Carrión et al. (2015) (link). Sediment samples were autoclaved twice and used as controls to show that variations in MeSH and DMS concentrations in the headspace were due to biological activity.

The chemicals and reagents used in this study came from the following sources: L-methionine derived from (Merk, Germany). Sodium methanethiolate was purchased from Sigma-Aldrich, Commassi Brilliant Blue G-250, 5,5-Dithiobis-2-nitrobenzoicacid (DTNB), pyridoxal-5-phosphate (PLP), and bovine serum albumin (BSA) (Sigma, St. Louis, USA). Pharmacia Biotechnology provided Sephadex G-100 and DEAE-cellulose (Sweden). Potato dextrose agar (PDA) (Conda lab, Spain). The American Type Culture Collection provided cancer and normal cells for this study (ATCC, Rockville, MD, USA). The rest of the compounds are of the highest analytical quality.

To study DMS production from MeSH by different environments, 1 g or 20 ml of sample was placed in a 125 ml serum vial containing distilled water supplemented with Y minimal medium 5% (Beringer, 1974 (link)), succinate (5 mM, Sigma-Aldrich, Dorset, UK) and MeSH added as sodium methanethiolate (20 μmol, Sigma-Aldrich) as described in Supplementary Methods. Additions of sodium methanethiolate will subsequently be referred to as additions of MeSH. All experiments were done in triplicate and vials were sealed prior to incubation at 22 °C for 24 h. MeSH and DMS headspace concentrations were measured by gas chromatography (GC) as described by Carrión et al., 2015 (link).