Microbial synthesis and enzymatic degradation of renewable poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate

Abstract

This paper reports our recent progress on a microbial system for efficient production of biodegradable copolyester of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate], P(3HB-co-3HHx), with desirable copolymer compositions using genetically engineered bacteria. We have developed a fermentation technique to achieve high cell density cultivation of a recombinant Ralstonia eutropha using inexpensive soybean oil as a sole carbon source. In addition, we demonstrate that the use of polyhydroxyalkanoate (PHA) synthase (PhaC) mutants having an amino acid substitutions is able to vary the copolymer composition of P(3HB-co-3HHx) synthesized from soybean oil by the recombinant bacteria. On the other hand, it is also important to understand the enzymatic degradation process of PHA materials for establishing a method to regulate the rate of biodegradation. The enzymatic degradation process of P(3HB-co-3HHx) thin film using an extracellular PHB depolymerase has been studied by in situ atomic force microscopy in buffer solution. We demonstrate that the PHA depolymerase predominantly degrades the less-ordered molecular chain-packing regions along the crystallographic a-axis.