Total variability vs. growth rate, in aerobic conditions. Red square corresponds to fixing glucose uptake at different values between 0 and 10 (keeping growth free), green square corresponds to fixing growth upper bound (keeping growth lower bound at zero and glucose uptake free), black circle corresponds to fixing growth lower bound (keeping growth upper bound at maximum growth and glucose uptake free) and blue circle corresponds to fixing upper and lower growth bounds at the same value (keeping glucose uptake free). Red square curve shows that growth limitation by glucose uptake produces an approximately proportional reduction in flux variability. Green square curve indicates that fixing growth upper bound has a negligible effect on flux variability. Black circle and blue circle curves show that fixing growth lower bound or both bounds have the same effect. Therefore, high flux variability requires that glucose uptake is high, so that the organism can grow at a potentially high rate, and that growth rate can be regulated to much lower values than the potential maximum growth.