Molecular weight modulation in polyhydroxybutyrate fermentations

Abstract

Polyhydroxybutyrate (PHB) is a material with significant potential for commercial applications. It has material properties similar to isotactic polypropylene; it can be produced from renewable resources; it is biodegradable. Unfortunately, it is very brittle when compared to polypropylene. The physical property that most significantly affects elastic behavior is molecular weight. In an effort to understand how molecular weight is formed in PHB production, kinetic studies of PHB fermentations have been performed using fermentation conditions which allow biomass growth and PHB production phases to be separated. These data indicate that molecular weight increases very quickly and then remains fairly constant in PHB fermentations. Additional studies have indicated that only slight changes in molecular weight can be caused by changing fermentation process conditions or using mutants of the polymerization enzyme. Additionally, one mutant polymerization enzyme has been shown to excrete moderate levels of PHB monomer, 3-hydroxybutyrate, into the fermentation media. This may have application in achieving synthetic production of PHB.