Biosynthesis of High Quality Polyhydroxyalkanoate Co- and Terpolyesters for Potential Medical Application by the Archaeon Haloferax mediterranei

Summary : Haloferax mediterranei was investigated for the production of two different high-performance polyhydroxyalkanoates (PHAs). A copolyester containing 6 mol-% 3-hydroxyvalerate (3HV) was produced from whey sugars as sole carbon source. The maximum specific growth rate (µ_max.) and the maximum specific PHA production rate (q_{p max.}) were determined with 0.10 1/h and 0.15 1/h, respectively. The cells contained 72.8 wt.-% of P-(3HB-co-6%-3HV) which featured low melting points between 150 and 160 °C and narrow molecular mass distribution (polydispersity PDI = 1.5). Further, a PHA terpolyester with an increased 3HV fraction as well as 4-hydroxybutyrate (4HB) building blocks was accumulated by feeding of whey sugars plus 3HV - and 4HB precursors. Kinetic analysis of the process reveals a µ_max. of 0.14 1/h and a q_{p max.} of 0.23 1/h, respectively. The final percentage of P-(3HB-co-21.8%-3HV-co-5.1%-4HB) in biomass amounted to 87.5 wt.-%. Also this material showed a narrow molecular mass distribution (PDI = 1.5) and a high difference between the two melting endotherms of the material (between 140 and 150 °C) and the onset of decomposition at 236 °C. The accomplished work provides viable strategies to obtain different high-quality PHAs which might be potential candidates for application in the medical and pharmaceutical field.