Studies on Synthesis of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) by a Sinorhizobium fredii Strain

Abstract:

The potential of a Sinorhizobium fredii strain producing a copolymer polyhydroxyalkanoate (PHA) from glucose and sodium decanoate substrates was studied in this paper. Using orthogonal design in a flask-shaker culture system, the culture medium, some culture conditions and vital regulation conditions for polymer synthesis were optimized. These optimized results were applied into further studies in two-stage fed-batch with a 10L fermentor. The whole culture process consisted of two stages, that is, the cell growth and the copolymer production. The first stage was for the cell growing to a desired biomass and the second was for the copolymer synthesis. For producing PHA polymers, the selected 8 mM sodium decanoate was added into the broth by adopting a two-step adding method for avoiding of foaming when the biomass had approached 28.5g/L dry cell. The maximum P (HB-HH) production could be 17.55g/L with a monomer ratio of 79.4% (W/W) 3-HB and 20.6% (W/W) 3-HH. The molecule constitute of the copolymer is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) ［P (HB-HH)］ and its molecular weight (MW) is 1.4×10⁵D. The results demonstrated that the employed S.fredii strain could be a potential candidate for industrial production of the copolymer. The fermentation parameters acquired in the experimental system offered some valuable references for studying large-scale production of the copolymer.

Key words:Sinorhizobium fredii, Sodium decanoate, Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), Fed-batch