Preparation of Quorum Sensing Signaling Compounds

3-Oxo-hexanoyl-homoserine lactone (3OC6-HSL) was purchased from Sigma-Aldrich (St. Louis, MO, USA). Stock solutions (1–10 mM) were prepared by dissolving appropriate amounts of 3OC6-HSL in ethyl acetate (Nacalai Tesque, Kyoto, JP) acidified with glacial acetic acid (0.01% (v/v); Nacalai Tesque, Kyoto, JP) and stored at -20°C. 6-(β-D-2-Deoxyribofuranosyl)-3,4-dihydro-8H-pyrimido[4 (link),5 (link)-c][1 (link),2 (link)]oxazin-7-one (dP) was purchased from Berry and Associates (Dexter, MI, USA). Stock solutions (1–1,000 μM) were prepared by dissolving appropriate amounts of dP in DMSO as 1,000 × stock (stored at 4°C). The oligonucleotides used in this work were all synthesized by FASMAC Co., Ltd (Kanagawa, JP). All other chemicals and media were of the highest available grade. Antibiotics were added to the growth medium as required at the following concentrations: 50 μg/mL carbenicillin (Carb; Sigma-Aldrich, St. Louis, MO, USA), 30 μg/mL chloramphenicol (Cm; Nacalai Tesque, Kyoto, JP), and 50 μg/mL kanamycin (Km; Sigma-Aldrich, St. Louis, MO, USA).