Production of two phase polyhydroxyalkanoic acid granules in Ralstonia eutropha

Aaron S. Kelley, Friedrich Srienc

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22 Scopus citations


To synthesize layered granules consisting of selected phases of polyhydroxybutyrate (PHB) homopolymer and PH(B-co-V) copolymer, Ralstonia eutropha was grown on fructose and limited quantities (1 g/l) of valeric acid. Exhaustion of the valerate resulted in a carbon source shift and a shift in the composition of polyhydroxyalkanoate (PHA) being synthesized within the cell. The synthesis rates were 0.030 g PH(B-co-V)/l per h and 0.033 g PHB/l per h, giving a copolymer composition of 48% HV. The valerate was exhausted at approximately 12 h at a rate of 0.0894 g/l per h after which only PHB was produced through the remaining 12 h at 0.033 g PHB/l per h from the remaining fructose, which was utilized at a constant rate of 0.0861 g/l per h throughout all 24 h of the experiment. Differential scanning calorimetry (DSC) of isolated granules showed two glass transitions, confirming the presence of two distinct polymer phases within the layered granules. Transmission electron microscopic images stained with RuO4 revealed a heavily stained copolymer core within a lighter stained PHB shell, confirming the expected morphology of granule composition. Thus, biosynthesis can be exploited for the control of domain sizes in layered granules, potentially providing metabolic control over the physical properties of the resultant polymer.

Original languageEnglish (US)
Pages (from-to)61-67
Number of pages7
JournalInternational Journal of Biological Macromolecules
Issue number1-3
StatePublished - Jun 1999

Bibliographical note

Funding Information:
This research was funded by the Consortium for Plant Biotechnology Research and a National Institutes of Health (NIH) training grant in biotechnology. The authors would like to thank Professor Chris Macosko, University of Minnesota, Department of Chemical Engineering and Materials Science for his consultation and review of this manuscript. Also, we would like to thank Kim Chaffin for her guidance in RuO 4 staining of polymers, as well as Chris Hall for his aid with electron microscopy.


  • Polyhydroxyalkanoate granules
  • Polyhydroxyalkanoates (PHAs)
  • Polymer blends
  • Polymer staining
  • Ralstonia eutropha
  • Transmission electron microscopy


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