2.7 Molecular weight determination of the exobiopolymers The average molecular weight of the polymers was determined by gel-permeation chromatography (GPC) (Waters 600E; Waters, MA, USA); the machine is equipped with a refractive index (RI) detector and an Ultrahydrogel linear column (300´7.8 mm ID; Waters, USA). Universal calibration log (Mp) versus VR, where Mp is the peak molecular weight, was conducted with dextran standards of molecular weights ranging from 4,400 to 401,000. Injection volume was 20 µl and flow rate of the mobile phase (0.05 M sodium bicarbonate buffer) was 0.6 ml/min.