Abstract
Itaconic acid is used as a bio-based, renewable building block in the polymer industry. It is produced by submerged fermentations of the filamentous fungus Aspergillus terreus from molasses or starch, but research over the efficient utilization of non-food, lignocellulosic plant biomass is soaring. The objective of this study was to test whether the application of two key cultivation parameters for obtaining itaconic acid from D-glucose in high yields – Mn2+ ion deficiency and high concentration of the carbon source – would also occur on D-xylose, the principal monomer of lignocellulose. To this end, a carbon and energy balance for itaconic acid formation was established, which is 0.83 moles/mole D-xylose. The effect of Mn2+ ions on itaconic acid formation was indeed similar to that on D-glucose and maximal yields were obtained below 3 μg L–1 Mn2+ ions, which were, however, only 0.63 moles of itaconic acid per mole D-xylose. In contrast to the case on D-glucose, increasing D-xylose concentration over 50 g L–1 did not change the above yield. By-products such as xylitol and α-ketoglutarate were found, but in total they remained below 2% of the concentration of D-xylose. Mass balance of the fermentation with 110 g L–1 D-xylose revealed that >95% of the carbon from D-xylose was accounted as biomass, itaconic acid, and the carbon dioxide released in the last step of itaconic acid biosynthesis. Our data show that the efficiency of biomass formation is the critical parameter for itaconic acid yield from D-xylose under otherwise optimal conditions.
Highlights
Itaconic acid (2-methylene-succinic acid, 2-methylidenebutanedioic acid; IA) is a well-known example of fungal overflow metabolism, the phenomenon of metabolic deregulation caused by a combination of carbon source abundance and serious shortage of phosphate and some micronutrient(s), of which Mn2+ ion limitation is the most important one (Batti and Schweiger, 1963; Rychtera and Wase, 1981; Kuenz et al, 2012; Karaffa et al, 2015)
To make sure that kinetics of fungal biomass, IA and residual D-xylose concentrations of the two cultivation systems would be independent of the vessel type, we ensured that the physical parameters were identical
We have tested the hypothesis that the application of two key parameters for obtaining IA by submerged fermentation from D-glucose in high yields – a deficiency in Mn2+ ions and a carbon source concentration of >100 g/L – would result in yields of IA from D-xylose close to the theoretical maximum
Summary
Itaconic acid (2-methylene-succinic acid, 2-methylidenebutanedioic acid; IA) is a well-known example of fungal overflow metabolism, the phenomenon of metabolic deregulation caused by a combination of carbon source abundance and serious shortage of phosphate and some micronutrient(s), of which Mn2+ ion limitation is the most important one (Batti and Schweiger, 1963; Rychtera and Wase, 1981; Kuenz et al, 2012; Karaffa et al, 2015). Due to the double bond of its methylene group, IA is mainly used as a bio-based, renewable building block in the polymer industry for the production of synthetic fibers, resins, plastics, coatings, and thickeners (Okabe et al, 2009). In principle, it could replace petroleum-based methacrylic and acrylic acid, thereby opening up a huge market (El-Imam and Du, 2014). Stiff competition with food applications keeps the fermentation industry searching for cheap, renewable raw materials to be utilized as carbon sources. Studies on IA production from D-xylose have been performed decades ago (Eimhjellen and Larsen, 1955; Kautola et al, 1985; Kautola, 1990), and reinitiated in recent years (Saha et al, 2017, 2019; Wu et al, 2017; Saha and Kennedy, 2019)
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