Poly(β-hydroxybutyric acid) thermoplastic production by Alcaligenes latus: Behavior of fed-batch cultures

Abstract

Fed-batch culture of Alcaligenes latus, ATCC 29713, was investigated for producing the intracellular bioplastic poly(β–hydroxybutyric acid), PHB. Constant rate feeding, exponentially increasing feeding rate, and pH-stat fed batch methods were evaluated. pH-stat fed batch culture reduced or delayed accumulation of the substrate in the broth and led to significantly enhanced PHB productivity relative to the other modes of feeding. Presence of excessive substrate appeared to inhibit PHB synthesis, but not the production of cells. In fed-batch culture, the maximum specific growth rate (0.265 h−1) greatly exceeded the value (0.075 h−1) previously observed in batch culture of the same strain. Similarly, the maximum PHB production rate (up to 1.15 g · l−1 · h−1) was nearly 8-fold greater than values observed in batch operations. Fed-batch operation was clearly superior to batch fermentation for producing PHB. A low growth rate was not a prerequisite for PHB accumulation, but a reduced or delayed accumulation of substrate appeared to enhance PHB accumulation. Under the best conditions, PHB constituted up to 63% of dry cell mass after 12 h of culture. The average biomass yield coefficient on sucrose was about 0.35, or a little less than in batch fermentations. The highest PHB concentrations attained were about 18 g · l−1.