L arginine monohydrochloride

Bovin serum albumin, catalase from bovine liver lyophilised powder (2000–5000 units/mg protein), ethanol, hydrogen peroxide solution (30% w/w in H₂O), methanol, polyvinylpyrrolidone (55 kDa), potassium hydroxide, Purpald^®, sodium chloride, sodium citrate tribasic dihydrate, and sodium phosphate monobasic monohydrate were supplied by Sigma-Aldrich (Steinheim, Germany). Citric acid, L-arginine monohydrochloride, dextran (~70 kDa), and 2,2,2-trifluoroethanol (>99%) were provided by Alfa Aesar (Heysham, UK). Ethylene diaminetetraacetic acid disodium salt dihydrate (EDTA), sodium phosphate dibasic dihydrate, aqueous formaldehyde solution (35 wt%) and hydrochloric acid (36.5–38% in water) were obtained from Honeywell (Seelze, Germany). Potassium periodate was purchased from Scientific Laboratory Suppliers Ltd. (Nottingham, UK). Ficoll PM70 (polysucrose 70) was obtained from Cytiva (Uppsala, Sweden). The Bradford 5× reagent was obtained from Serva (Heidelberg, Germany) and a microBCA protein assay kit was sourced from ThermoFisher (Rockford, IL, USA). Super refined Polysorbate 20^® and super refined Polysorbate 80^® were obtained from Croda (Goole, UK). α,α-Trehalose dihydrate was purchased from Pfanstiehl (Waukegan, IL, USA).

Streptococcus dentisani 7746 was grown in 300 ml of BHI medium amended with 5 g/l of L-arginine monohydrochloride 98% (Alfa-Aesar). The pre-inoculum was obtained by inoculating a single colony of the strain in 10 ml of BHI broth and incubating overnight at 37°C without agitation. Inoculation was made with the volume required to obtain an initial O.D. ₆₁₀ of 0.02. For comparison, the same volume was used to inoculate 300 ml of BHI without arginine. In both conditions the initial pH was set at 7.3. The cultures were incubated at 37°C during 24 h and aliquots of 1 ml were taken every hour for measuring the pH and the O.D. ₆₁₀. Both conditions were assayed by triplicate.