Tailored Synthesis of Poly([R]-3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/HV) in Ralstonia eutropha DSM 428

• Published in: Acta biotechnologica 2003-01, Vol.23 (2-3), p.309-316
• Main Authors: Zinn, M., Weilenmann, H.-U., Hany, R., Schmid, M., Egli, Th
• Format: Article
• Language: English
• Subjects: ammonium; butyric acid; poly(3-hydroxybutyrate-co-3-hydroxyvaleric acid); poly(3-hydroxybutyric-co-3-hydroxyvaleric acid); Ralstonia eutropha; valeric acid
• ISSN: 0138-4988; 1521-3846
• DOI: 10.1002/abio.200390039

Ralstonia eutropha was grown in a chemostat at a dilution rate of D = 0.1 ± 0.01 h−1 under the conditions of simultaneous limitation by carbon (butyric and/or valeric acid) and nitrogen (ammonium). In order to achieve a physiological state with a high cellular polyhydroxyalkanoate (PHA) content, the ratio of total carbon to nitrogen of the feed medium was kept constant at 17 mol C/molN and only the ratio of butyric to valeric acid was varied in the carbon feed. When only butyric acid was fed, poly([R]‐3‐hydroxybutyrate) (PHB) was isolated. For substrate mixtures consisting of butyric and valeric acid, and valeric acid alone, the co‐polymer poly([R]‐3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHB/HV) was incorporated with a maximum content of (R)‐3‐hydroxyvalerate of 62 mol%. The melting temperature of PHA decreased from 178 °C for PHB to about 80 °C for PHA with the highest HV content. The molecular weight (Mw) of the polymer was between 0.9 and 1.2 × 106 with a polydispersity of 3 ± 0.3. The polymer composition in the cells was a non‐linear function of the substrate mixture. It was concluded that dual (C, N) limited growth conditions in chemostat cultures could be used to tailor the composition of PHB/HV in an accurate way, which is not possible when using N limited batch cultures.