Vitamin solution

For the plant physiology assay, we sterilized WT and OE seeds with PPM and maintained them in darkness at 4 °C for three days. Immediately after this period, the seeds were placed in a low-calcium (0.2 mM CaCl₂) ½ MS agar medium, with or without 60 mM NaCl. The ½ MS agar medium comprised the vital components of major salts (NH₄NO₃, MgSO₄, KH₂PO₄, and KNO₃; Sigma), a vitamin solution (Sigma), 0.5% sucrose (Sigma), and 0.6% agar (Sigma), with the calcium content increased to 0.2 mM CaCl₂. Following a growth period of 12 days, we evaluated the seedling root lengths as part of our analysis.
The seeds were also placed in a normal-calcium (2.5 mM CaCl₂) ½ MS agar medium, with or without 60 mM NaCl. Following a growth period of 8 days, we evaluated seedling root lengths as part of our analysis.

Haloferax volcanii strain H26 was kindly provided by Thorsten Allers (University of Nottingham, UK). It was and grown in complex medium [36] (link) or in synthetic medium [37] (link) supplemented with 8 µM FeSO₄ (Roth, P015.1), 0,1% (v/v) SL-6 trace element solution [38] (link) (all from Roth), 1 ml vitamin solution (Sigma Aldrich, B6891), 50 µg ml⁻¹ uracil (Applichem, A0667) and 100 mM MOPS pH 7.2 (Sigma Aldrich, M3183). All components of the synthetic medium were of the grade “per analysis” and thus free of phosphate, e.g. K₂HPO₄ (Roth, 6878.2), NH₄Cl (Applichem, A0988), glucose (Merck, 1083441000), NaCl (Roth, 3957.5), MgCl₂ (Roth, 2189.1), MgSO₄ (Applichem, A1037), KCl (Roth, 6781,1), CaCl₂ (Applichem, A3587), and Tris (A1086). If not otherwise stated, the synthetic medium was also supplemented with 0.5% (w/v) glucose as a C source, 10 mM NH₄Cl as a N source, and 1 mM K₂HPO₄ as a P source. For growth experiments with DNA as a source of P K₂HPO₄ was omitted and genomic DNA was added to a final concentration of 250 µg/ml. Cultures were grown in Erlenmeyer flasks in a rotary shaker at 42 °C and 250 rpm or in microtiter plates as described below.

On the day of the experiment, each reactor was filled with 90 mL of gastrointestinal (GI) food that consisted of arabinogalactan (1 g/L), pectin (2 g/L), glucose (0.4 g/L), xylan (1 g/L), starch (3 g/L), mucin (4 g/L), proteose peptone (1 g/L), yeast extract (3 g/L), L-cysteine (0.5 g/L), NaHCO₃ (0.4 g/L), Tween 80 (1 mL/L), vitamin solution (40 μL/L) (Sigma Aldrich, St. Louis, MO, USA) and autoclaved distilled water. The pH of GI food was adjusted to seven before use. The formula of GI food was based on Molly et al. (48 ), which has been shown to provide optimal growth conditions for commensal gut bacteria.