Efficient calcium fumarate overproduction from xylose and corncob-derived xylose by engineered strains of Aureobasidium pullulans var. Aubasidani DH177.

Background: Xylose from lignocellulose is one of the most abundant and important renewable and green raw materials. It is very important how to efficiently transform xylose into useful bioproducts such as fumaric acid and so on.

Results: In this study, it was found that the GC1 strain (∆gox, in which the GOX gene encoding glucose oxidase which could transform glucose into gluconic acid was removed) of A. pullulans var. aubasidani DH177 had the high ability to utilize xylose and corncob-derived xylose with CO₂ fixation derived from CaCO₃ to produce calcium fumarate. Overexpression of the XI gene encoding xylose isomerase, the XK gene encoding xylose kinase and the TKL gene coding for transketolase made the strain TKL-4 produce 73.1 g/L of calcium fumarate from xylose. At the same time, the transcriptional levels of the key ASS gene coding for argininosuccinate synthase and the ASL gene coding for argininosuccinate lyase in the ornithine-urea cycle (OUC) were also obviously enhanced. The results also demonstrated that the TKL-4 strain could produce more calcium fumarate from xylose and corncob-derived xylose than from glucose. During 10-liter fermentation, the TKL-4 strain could produce 88.5 g/L of calcium fumarate from xylose, the productivity was 0.52 g/h/L. Meanwhile, it could yield 85.6 g/L of calcium fumarate from corncob-derived xylose and the productivity was 0.51 g/h/L. During the same fermentation, the TKL-4 strain could transform the mixture containing 75.0 g/L glucose and 45.0 g/L xylose to produce 78.7 ± 1.1 g/L calcium fumarate.

Conclusions: This indicated that the TKL-4 strain constructed in this study indeed could actively transform xylose and corncob-derived xylose into calcium fumarate through the green ways.