Synthesis of poly (3-hydroxybutyrate-co-3-hydroxyoctanoate) by a Sinorhizobium fredii strain

The potential of a Sinorhizobium fredii strain to produce a copolymer from glucose and sodium dodecanoate substrates was investigated.

Using an orthogonal design in a flask-shaker culture system, the vital regulation conditions for copolymer synthesis were optimized. These optimal results were applied to further studies in a two-stage fed-batch fermentation with a 10-l fermentor. When the biomass approached 33.5 g l(-1) dry cells at 35 h, 7 mmol l(-1) sodium dodecanoate was added into the broth to trigger the copolymer synthesis. After further culturing for 3 h, the copolymer product could be 17.14 g l(-1). The molecular structure of the copolymer was determined to be a poly (3-hydroxybutyrate-co-3-hydroxyoctanoate) [P (HB-HO)] by nuclear magnetic resonance. The content of HB and HO in P (HB-HO) was 79.2% (w/w) and 20.8% (w/w) respectively. The molecular weight of the P (HB-HO) was measured as 1.85 x 10(5) Da by a viscosity method.

The results demonstrated that the S. fredii strain used could be a potential candidate for the industrial production of the copolymer.

Some basic fermentation parameters were acquired through the fed-batch culturing experiments and they should be applicable in developing large-scale fermentation technologies for producing the P (HB-HO) copolymers.