Dipotassium hydrogen phosphate

L. plantarum (DSM 20205), L. brevis (DSM 6235) and L. paracasei (DSM 20312) were obtained from the German Collection of Microorganisms and Cell Cultures GmbH (Braunschweig, Germany), while L. rhamnosus (NCTC 10302) was purchased from the National Collection of Type Cultures (NCTC, Salisbury, UK). All strains were cultivated microanaerobically in de Man, Rogosa and Sharpe (MRS) broth (Carl Roth GmbH, Karlsruhe, Germany) under agitation at 37 °C. Modified MRS (pH 6.5 ± 0.2) was prepared in-house by dissolving 10 g of peptone from casein, 4 g of yeast extract, 6 g dipotassium hydrogen phosphate, 5 g of diammonium hydrogen citrate and 0.04 g of manganese sulphate per liter (all Carl Roth GmbH). The medium was heat-treated by autoclaving at 121 °C for 12 min and stored at 4 °C before use.
Gram staining was performed with a Gram staining kit (Merck, Darmstadt, Germany) according to the manufacturer’s instructions. Cells were observed via light microscopy (Nikon Eclipse 80i, objective Plan Fluor 100 × 1.30; Nikon Instruments, Amsterdam, Netherlands) using differential interference contrast (DIC). Photos were taken with the Nikon DS U1 camera (5 MPx) using the NIS-Elements software (Version 5.02.01, Nikon Instruments).

Hydrochloric acid (HCl, ACS reagent, 37%, Sigma Aldrich, St. Louis, MO, USA), sodium hydroxide (NaOH, >97%, Sigma Aldrich), sodium chloride (NaCl, >99.5%, Sigma Aldrich), acetic acid (AA, 100%, Roth, Karlsruhe, Germany), potassium dihydrogen phosphate (>99%, Roth), dipotassium hydrogen phosphate (>99%, Roth), pullulan (standard set, M_w 320–740,000 g/mol, Sigma Aldrich) were used in the following experiments. Ultrapure (UP) water was produced by an arium^®pro ultra-pure water system (Sartorius Stedim Biotech GmbH, Goettingen, Germany). The monoclonal antibodies (mAb1 (MW: 145.5 kDa; isoelectric point (pI): 8.7) and mAb2 (MW: 144.2 kDa; pI: 8.3)) were kindly donated by Sartorius Stedim Biotech.

Agar, yeast cell extract, dipotassium hydrogen phosphate (K₂HPO₄), magnesium sulfate (MgSO₄), ferrous sulfate (FeSO₄), calcium carbonate (CaCO₃), sodium chloride (NaCl), and D-(+)-glucose (C₆H₁₂O₆) were purchased from Carl Roth GmbH & Co. (Karlsruhe, Germany). Both 2-methyl-1,4-naphthoquinone (C₁₁H₈O₂) and riboflavin (C₁₇H₂₀N₄O₆) were purchased from Alfa Aesar (Haverhill, MA, USA). Sodium molybdate (Na₂MoO₄) and 9,10-phenanthrenequinone (C₁₄H₈O₂) were purchased from Merck (Darmstadt, Germany). Yeast cell extract and glucose were of microbiological grade. The other chemicals were GPR-grade.