Rhizopus oryzae for fumaric acid production: optimising the use of a synthetic lignocellulosic hydrolysate

<p>The hydrolysis of lignocellulosic biomass opens an array of bioconversion possibilities for producing fuels and chemicals. </p> <p>Microbial fermentation is particularly suited to the conversion of sugar rich hydrolysates to biochemicals. Rhizopus oryzae ATCC 20344 was employed to produce<br> fumaric acid from glucose, xylose and a synthetic lignocellulosic hydrolysate (glucose-xylose mixture) in batch and continuous fermentations. </p> <p>A novel immobilised biomass reactor was used to investigate the co-fermentation of xylose and glucose. Ideal medium conditions and a substrate feed strategy were then employed to optimise for the production of fumaric acid. The batch fermentation of the synthetic hydrolysate at the optimal conditions (urea feed rate 0.625 mg L⁻¹ h⁻¹and pH 4) produced a fumaric acid yield of 0.439 g g−1. A specific substrate feed rate (0.164 g L⁻¹ h⁻¹) which negated ethanol production and selected for fumaric acid was determined. Using this feed rate in a continuous fermentation a fumaric acid yield of 0.735 g g⁻¹ was achieved; a 67.4 % improvement. Metabolic analysis helped to determine a continuous synthetic lignocellulosic hydrolysate feed rate that selected for fumaric acid production, while achieving co-fermentation of glucose and xylose, avoiding the undesirable carbon catabolite repression. </p> <p>This work demonstrates the viability of fumaric acid production from lignocellulosic hydrolysate; the process developments discovered will pave the way for an industrially viable process. </p>