Control of Molecular Weight Distribution and Mole Fraction in Poly(-D(−)-3-hydroxyalkanoate) (PHA) Production by Alcaligenes eutrophus

Abstract

Kinetics of poly(-D(−)-3-hydroxyalkanoate) (PHA) production were studied in Alcaligenes eutrophus H16 (ATCC 17699) fed-batch culture using butyric acid and valeric acid as carbon sources. In poly(-D(−)-3-hydroxybutyric acid) (PHB) production, at the conditions of 3g/l butyric acid concentration and pH 8.0, the maximum values of specific production rate of PHB, production yield, and PHB content in the cell were obtained. Effect of cultivation condition on molecular weight distribution of PHB was studied. The average of molecular weight was decreased as the butyric acid concentration was increased. When the nitrogen source was added to the fermentation medium after adequate PHB accumulation in the cell, not only PHB production but also degradation were simultaneously occurred. The degradation rate of low molecular weight polymer was higher than that of high molecular weight polymer, and as a result, the average of molecular weight distribution shifted to the higher value. By addition of valeric acid to the butyric acid as carbon sources, copolyester of 3-hydroxybutyric acid (3HB) and 3-hydroxyvaleric acid (3HV), which is abbreviated as P(3HB-co-3HV), was produced but the specific production rate was lower than that of PHB. The mole fraction of P(3HB-co-3HV), was also investigated, using butyric acid and valeric acid as carbon sources. The mole fraction can be controlled within a range of compositions (0-40 mole% 3HV) by the mole ratio of butyric acid and valeric acid in the feeding medium.