Figure 2

Optimization of induction conditions for maximal rNuc production. Cultures of strain 918 grown in GM17v using LacMF were induced by the addition of EDTA at different time points (A) or concentrations (B) or both (C). In (A) and (B), both bacterial growth (solid lines) and rNuc concentration into the medium (dotted lines, calculated by comparison to a quantified standard on stained gels) are shown as a function of time (↓ indicates EDTA addition time point). As before induction, rNuc level was undetectable for mid-exponential phase cultures (at OD₆₀₀ 2 and 4), an arbitrary value (1 mg/L, corresponding to the sensitivity threshold of our staining method) is indicated (black star). (A) rNuc levels as a function of time after induction of a culture at different growth stages by highly concentrated EDTA. 1 mM EDTA was added or not (black square) to parallel cultures at different OD₆₀₀, i. e. 2 (black diamond), 4 (black circle) or 8 (X). (B) rNuc level as a function of time after induction of an exponential phase culture by EDTA at different concentrations. Cultures at OD₆₀₀ 2 were induced or not (black square) by EDTA at various concentrations: 100 μM (black triangle), 500 μM (upside down black triangle) or 1 mM (black diamond). (C) Final rNuc level as a function of both induction OD₆₀₀ and EDTA concentration. Final rNuc concentration in the medium after prolonged growth (8 h-9 h of culture) is shown.