Glycerine and levulinic acid: Renewable co-substrates for the fermentative synthesis of short-chain poly(hydroxyalkanoate) biopolymers

Abstract

Glycerine (a biodiesel co-product) and levulinic acid (a pulp and paper co-product) were used as co-substrates for the fermentative synthesis of short-chain polyhydroxyalkanoate (sc-PHA) biopolymers with tunable monomer and molecular weight characteristics. Pseudomonas oleovorans NRRL B-14682 utilized glycerine alone to produce poly(3-hydroxybutyrate) (PHB). When levulinic acid was added to the media at shake-flask scale in concentrations ⩽0.6wt.%, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/V) copolymers were produced with 3-HV contents ranging from 37 to 97mol%; a glycerine:levulinic acid ratio of 0.2%:0.8% (w/v) resulted in poly(3-hydroxyvalerate) (PHV). Ten-liter batch fermentations using glycerine:levulinic acid ratios of 1%:0, 0.75%:0.25%, 0.5%:0.5% and 0.25%:0.75% (w/v) resulted in PHB, P(73%-3HB-co-27%-3HV), P(30%-3HB-co-70%-3HV) and PHV with increasing number average molecular weights (×103g/mol) of 328, 511, 728 and 1330, respectively, owing to glycerine-based chain termination. These results provide a novel means by which glycerine and levulinic acid can be used collectively to produce an array of distinct sc-PHA biopolymers.