Studies on intracellular degradation of polyhydroxyalkanoic acid–polyethylene glycol copolymer accumulated by Azotobacter chroococcum MAL-201

Azotobacter chroococcum MAL-201 accumulates poly(3-hydroxybutyric acid) [PHB] when grown in glucose containing nitrogen-free Stockdale medium. The same medium supplemented with valerate alone and valerate plus polyethylene glycol (PEG) leads to the accumulation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] and PEG containing PHBV–PEG polymers, respectively. The intracellular degradation of these polymers as studied in carbon-free Stockdale medium showed a rapid degradation of PHB followed by PHBV, while it was least in case of PHBV–PEG. The rate of such degradation was 44.16, 26.4 and 17.0 mg h−1 l−1 for PHB, PHBV and PHBV–PEG, respectively. During the course of such of PHBV and PHBV–PEG degradation the 3HB mol% of polymers decreased significantly with increase of 3HV mol fraction, the EG mol% in PHBV–PEG, however, remained constant. After 50 h of degradation the decrease in intrinsic viscosity and molecular mass of PHBV–PEG were 37.5 and 43.6%, respectively. These values appeared low compared to PHB and PHBV. Moreover, the increasing EG content of polymer retarded their extent of degradation. Presence of PEG, particularly of low molecular weight PEG was inhibitory to intracellular PHA depolymerise (i-PHA depolymerase) activity and the relative substrate specificity of the i-PHA depolymerase of MAL-201 appeared to be PHB > PHBV > PHBV–PEG.