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. 2017 Oct 23:10:242.
doi: 10.1186/s13068-017-0930-x. eCollection 2017.

Sustainable carbon sources for microbial organic acid production with filamentous fungi

Stefan Dörsam  1 , Jana Fesseler  1 , Olga Gorte  1 , Thomas Hahn  2 , Susanne Zibek  2 , Christoph Syldatk  1 , Katrin Ochsenreither  1
Affiliations

Sustainable carbon sources for microbial organic acid production with filamentous fungi

Stefan Dörsam et al. Biotechnol Biofuels. .

Abstract

Background: The organic acid producer Aspergillus oryzae and Rhizopus delemar are able to convert several alternative carbon sources to malic and fumaric acid. Thus, carbohydrate hydrolysates from lignocellulose separation are likely suitable as substrate for organic acid production with these fungi.

Results: Before lignocellulose hydrolysate fractions were tested as substrates, experiments with several mono- and disaccharides, possibly present in pretreated biomass, were conducted for their suitability for malic acid production with A. oryzae. This includes levoglucosan, glucose, galactose, mannose, arabinose, xylose, ribose, and cellobiose as well as cheap and easy available sugars, e.g., fructose and maltose. A. oryzae is able to convert every sugar investigated to malate, albeit with different yields. Based on the promising results from the pure sugar conversion experiments, fractions of the organosolv process from beechwood (Fagus sylvatica) and Miscanthus giganteus were further analyzed as carbon source for cultivation and fermentation with A. oryzae for malic acid and R. delemar for fumaric acid production. The highest malic acid concentration of 37.9 ± 2.6 g/L could be reached using beechwood cellulose fraction as carbon source in bioreactor fermentation with A. oryzae and 16.2 ± 0.2 g/L fumaric acid with R. delemar.

Conclusions: We showed in this study that the range of convertible sugars for A. oryzae is even higher than known before. We approved the suitability of fiber/cellulose hydrolysate obtained from the organosolv process as carbon source for A. oryzae in shake flasks as well as in a small-scale bioreactor. The more challenging hemicellulose fraction of F. sylvatica was also positively evaluated for malic acid production with A. oryzae.

Keywords: Aspergillus oryzae; Fermentation; Filamentous fungi; Levoglucosan; Lignocellulose; Malate; Malic acid; Organic acid; Organosolv; Rhizopus delemar.

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Figures

Fig. 1
Fig. 1
Examples of malic acid formation (a) and volumetric production rates (b) during cultivation of A. oryzae DSM 1863 by using different carbon sources. Flasks were incubated at 32 °C for 168 h. Q p = volumetric production rate
Fig. 2
Fig. 2
Carbon source and malic acid concentration during cultivation with A. oryzae DSM 1863 and cellulose/fiber hydrolysates from F. sylvatica (a) and M. giganteus (b). Flasks were incubated at 32 °C for 168 h
Fig. 3
Fig. 3
Malic acid concentration during cultivation of A. oryzae DSM 1863 with hemicellulose fraction from beechwood (BHF) in three different concentrations. Flasks were incubated at 32 °C for 168 h
Fig. 4
Fig. 4
Carbon source and malic acid concentration by fermentation of A. oryzae DSM 1863 with cellulose/fiber hydrolysate (a) and hemicellulose fraction (b) from F. sylvatica. Batch fermentation was carried out in a small-scale bioreactor at 35 °C and 300 rpm for 168 h
Fig. 5
Fig. 5
Carbon source and fumaric acid concentration by fermentation of R. delemar DSM 905 with cellulose hydrolysate from beechwood. Batch fermentation was done in a small-scale bioreactor at 35 °C and 300 rpm for 168 h
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