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

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/mol N 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 degreesC for PHB to about 80 degreesC for PHA with the highest HV content. The molecular weight (M-W) of the polymer was between 0.9 and 1.2 x 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.