[Biosynthesis of poly-3-hydroxybutyrate-3-hydroxyvalerate copolymer by Azotobacter chroococcum strain 7B]

The ability of Azotobacter chroococcum strain 7B, producer of polyhydroxybutyrate (PHB), to synthesize its copolymer poly-3-hydroxybutyrate-3-hydroxyvalerate (PHB-HV) was studied. It was demonstrated, for the first time, that A. chroococcum strain 7B was able to synthesize PHB-HV with various molar rates of HV in the polymer chain when cultivated on medium with sucrose and carboxylic acids as precursors of HV elements in the PHB chain, namely, valeric (13.1-21.6 mol %), propanoic (3.1 mol %), and hexanoic (2.1 mol %) acids. Qualitative and functional differences between PHB and PHB-HV were demonstrated by example of the release kinetic of methyl red from films made of synthesized polymers. Maximal HV incorporation into the polymer chain (28.8 mol %) was recorded when the nutrient medium was supplemented with 0.1% peptone on the background of 20 mM valerate. These results suggest that that the studied strain can be regarded as a potential producer of not only PHB but also PHB-HV.