Abstract

The ability of Rhizopus oryzae to produce fumaric acid in the presence of glycerol and/or various monosaccharides as carbon sources was examined for seventeen different strains of this fungi. These strains were tested in shake-flask cultures on media containing glycerol and seven different carbohydrates, including glucose, fructose, galactose, mannose, xylose, arabinose, and rhamnose. An interesting and applicationally useful phenomenon was observed. This work presents a new approach to the conventional microbiological method of producing fumaric acid. In the presence of 40 g/l glycerol as the sole carbon source, fumaric acid production reached 0.16–6.1 g/l after 192 h. When monosaccharides were used as a single carbon source, the maximum fumaric acid concentration was much higher; for example, 19.8 g/l was achieved when 40 g/l xylose was used. In the co-fermentation of xylose (40 g/l) and glycerol (20 g/l), post-culture broth contained approx. 28.0 g/l of fumaric acid with a process yield of 0.90 g/g after 168 h. The production of fumaric acid by Rhizopus oryzae was also increased in the dual presence of glycerol and monosaccharides like fructose, galactose, and mannose. However, results obtained on glucose-glycerol-based medium did not follow this trend, showing instead complete utilization of glucose with significant glycerol consumption, but unexpectedly low final amounts of fumaric acid and process yields. Understanding how Rhizopus oryzae utilize various carbon sources may provide alternative avenues of fumaric acid fermentation.

Highlights

  • In industrial biotechnology, feedstock is by far the highest cost factor in the production of chemicals, representing 40–60% of total costs (Demain 2007)

  • FA (g/l), fumaric acid concentration in medium after culture; X (g/l), xylose concentration in medium after culture; Gl (g/l), glycerol concentration in medium after culture; CV (%), consume value; ­Yfa/s (g/g), g of fumaric acid produced per g of carbon source consumed case, the production of fumaric acid was several times higher than after xylose alone as the sole carbon source

  • Different carbon sources had a significant impact on fumaric acid production by Rhizopus strains

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Summary

Introduction

Feedstock is by far the highest cost factor in the production of chemicals, representing 40–60% of total costs (Demain 2007). The production of fumaric acid from lignocellulosic biomass by Rhizopus fermentation has received a great deal of attention due to its extensive applications in the polymer, medical, and food industries. Our preliminary investigations showed that R. oryzae produced significantly lower amounts of fumaric acid with crude glycerol as the sole carbon source, when compared with glucose growth cultures (unpublished data). This glycerol utilization phenomenon can be seen from archaebacteria (Falb et al 2008) to human cells (Hibuse et al 2006). The oxidation route occurs in reverse; first glycerol oxidation by glycerol dehydrogenase yields dihydroxyacetone, this is phosphorylated to generate 3-P-dihydroxyacetone (Tom et al 1978). Dihydroxyacetone phosphate derived from either pathway can be shunted to the glycolytic or gluconeogenic pathway and further transformed (Fakas et al 2009; Turcotte et al 2010)

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