Influence of emulsified plant oil composition on growth and biopolymer production of Cupriavidus necator DSM 545

Abstract

Cupriavidus necator DSM 545 was cultivated on a range of crude and emulsified plant oils (olive, rapeseed, sesame seed, spent coffee grounds (SCGs) and sunflower) of varying fatty acid (FA) composition to assess their influence on the organism’s growth and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] biopolymer production. Initially five different surfactants (gum arabic, dimethyl sulfoxide (DSMO), Tween 80, Triton X-100, and sodium dodecyl sulfate) were screened for their influence on cell growth and ability to form stable oil-in-water emulsions. The highest total biomass (11.3 ± 0.2 g L−1) and P(3HB-co-3HV) (10.0 ± 0.6 g L−1) concentrations were achieved with SCGs oil emulsified with DMSO. At 88.9 ± 5.2%, the corresponding polymer fraction of the total biomass is among the highest values reported in the literature. During the initial growth phase (0–24 h), the organism consumed all fatty acids in broadly the same proportion, but preference was then displayed in the subsequent P(3HB-co-3HV) production phase (24–120 h) for saturated FAs (particularly palmitic acid) over unsaturated FAs. SCG oil was an ideal substrate in comparison to the other plant oils due to its high acid value (17.9 ± 0.1 mgKOH goil−1) and palmitic acid content (31.4 ± 0.5%, w/w). Emulsifying the plant oil cultures initially increased substrate bioavailability, but the influence diminished as the fermentations progressed. Overall, the use of SCGs as a feedstock for PHA production will help reduce the manufacturing costs of the biopolymer and generate a valorisation strategy for an otherwise highly unutilised resource.