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

Abstract

Abstract 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 ( M w ) of the polymer was between 0.9 and 1.2 × 10 6 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.