Polyhydroxybutyrate production from a novel feedstock derived from a wheat-based biorefinery

Abstract

A wheat-based biorefining strategy was evaluated for polyhydroxybutyrate (PHB) production by Cupriavidus necator (formerly classified as Ralstonia eutropha but currently designated Wautersia eutropha). Wheat was bioconverted into two feedstock streams, wheat hydrolysate (WH) and fungal extract (FE) that were rich in glucose and nitrogen, respectively. WH and FE were mixed in appropriate proportions to provide media with varying glucose (5–26 g l −1) and free amino nitrogen (FAN) (0.1–1.2 g l −1) concentrations for batch shake flask fermentations. Increasing FAN concentration resulted in higher microbial growth and less PHB accumulation. The consumption of various carbon sources (carbohydrates, amino acids, peptides) resulted in high growth yields (up to 1.07 g cells (g glucose) −1) as related to glucose. Specific growth rates up to 0.16 h −1 were observed. Three WH with similar glucose (200–220 g l −1) and varying FAN (0.3–1.48 g l −1) concentrations were evaluated in fed-batch shake flask fermentations for C. necator growth and PHB accumulation. The medium with the highest nitrogen concentration (WH3) gave the highest microbial biomass concentration (29.9 g l −1), growth yield (0.28 g residual microbial biomass (g glucose) −1) and PHB yield (0.43 g (g glucose) −1). WH2 gave the highest PHB concentration (51.1 g l −1) and content (0.7 g g −1).