Production ofD-arabitol by a metabolic engineered strain ofBacillus subtilis

Random mutagenesis and transcriptomics-guided rational engineering in Zygosaccharomyces rouxii for elevating D-arabitol biosynthesis

D-arabitol, a versatile compound with applications in food, pharmaceutical, and biochemical industries, faces challenges in biomanufacturing due to poor chassis performance and unclear synthesis mechanisms. This study aimed to enhance the performance of Zygosaccharomyces rouxii to improve D-arabitol production. Firstly, a mutant strain Z. rouxii M075 obtained via atmospheric and room temperature plasma-mediated mutagenesis yielded 42.0 g/L of D-arabitol at 96 h, with about 50 % increase. Transcriptome-guided metabolic engineering of pathway key enzymes co-expression produced strain ZR-M3, reaching 48.9 g/L D-arabitol after 96 h fermentation. Finally, under optimized conditions, fed-batch fermentation of ZR-M3 in a 5 L bioreactor yielded an impressive D-arabitol titer of 152.8 g/L at 192 h, with a productivity of 0.8 g/L/h. This study highlights promising advancements in enhancing D-arabitol production, offering potential for more efficient biomanufacturing processes and wider industrial applications.

High-level production of d-arabitol by Zygosaccharomyces rouxii from glucose: Metabolic engineering and process optimization

d-Arabitol is a top value-added compound with wide applications in the food, pharmaceutical and biochemical industries. Nevertheless, sustainable biosynthesis of d-arabitol is limited by lack of efficient strains and suitable fermentation process. Herein, metabolic engineering and process optimization were performed in Zygosaccharomyces rouxii to overcoming these limitations. Adopting systems metabolic engineering include enhancement of innate biosynthetic pathway, supply of precursor substrate d-ribulose-5P and cofactors regeneration, a novel recombinant strain ZR-5A with good performance was obtained, which boosted d-arabitol production up to 29.01 g/L, 59.31 % higher than the parent strain. Further with the optimum medium composition and fed-batch fermentation, the strain ZR-5A finally produced 149.10 g/L d-arabitol with the productivity of 1.04 g/L/h, which was the highest titer ever reported by Z.rouxii system. This is the first report on the use of metabolic engineering to construct Z. rouxii chassis for the sustainable production of d-arabitol.

Discovery and Functional Characterization of a Yeast Sugar Alcohol Phosphatase

Sugar alcohols (polyols) exist widely in nature. While some specific sugar alcohol phosphatases are known, there is no known phosphatase for some important sugar alcohols (e.g., sorbitol-6-phosphate). Using liquid chromatography-mass spectrometry-based metabolomics, we screened yeast strains with putative phosphatases of unknown function deleted. We show that the yeast gene YNL010W, which has close homologues in all fungi species and some plants, encodes a sugar alcohol phosphatase. We term this enzyme, which hydrolyzes sorbitol-6-phosphate, ribitol-5-phosphate, and (d)-glycerol-3-phosphate, polyol phosphatase 1 or PYP1. Polyol phosphates are structural analogs of the enediol intermediate of phosphoglucose isomerase (Pgi). We find that sorbitol-6-phosphate and ribitol-5-phosphate inhibit Pgi and that Pyp1 activity is important for yeast to maintain Pgi activity in the presence of environmental sugar alcohols. Pyp1 expression is strongly positively correlated with yeast growth rate, presumably because faster growth requires greater glycolytic and accordingly Pgi flux. Thus, yeast express the previously uncharacterized enzyme Pyp1 to prevent inhibition of glycolysis by sugar alcohol phosphates. Pyp1 may be useful for engineering sugar alcohol production.

Improved xylitol production by expressing a novel d-arabitol dehydrogenase from isolated Gluconobacter sp. JX-05 and co-biotransformation of whole cells

In the present study, a novel ardh gene encoding d-arabitol dehydrogenase (ArDH) was cloned and expressed in Escherichia coli from a new isolated strain of Gluconobacter sp. JX-05. Sequence analysis revealed that ArDH containing a NAD(P)-binding motif and a classical active site motif belongs to the short-chain dehydrogenase family. Subsequently, the optimal pH and temperature, specific activities and kinetic parameter of ArDH were determined. In the co-biotransformation by the whole cells of BL21-ardh and BL21-xdh, 26.1g/L xylitol was produced from 30g/L d-arabitol in 22h with a yield of 0.87g/g. The xylitol production was increased by more than two times as compared with that of Gluconobacter sp. alone, and was improved 10.1% than that of Gluconobacter sp. mixed with BL21-xdh.

Metabolic engineering of Saccharomyces cerevisiae for conversion of D-glucose to xylitol and other five-carbon sugars and sugar alcohols

Recombinant Saccharomyces cerevisiae strains that produce the sugar alcohols xylitol and ribitol and the pentose sugar D-ribose from D-glucose in a single fermentation step are described. A transketolase-deficient S. cerevisiae strain accumulated D-xylulose 5-phosphate intracellularly and released ribitol and pentose sugars (D-ribose, D-ribulose, and D-xylulose) into the growth medium. Expression of the xylitol dehydrogenase-encoding gene XYL2 of Pichia stipitis in the transketolase-deficient strain resulted in an 8.5-fold enhancement of the total amount of the excreted sugar alcohols ribitol and xylitol. The additional introduction of the 2-deoxy-glucose 6-phosphate phosphatase-encoding gene DOG1 into the transketolase-deficient strain expressing the XYL2 gene resulted in a further 1.6-fold increase in ribitol production. Finally, deletion of the endogenous xylulokinase-encoding gene XKS1 was necessary to increase the amount of xylitol to 50% of the 5-carbon sugar alcohols excreted.

Production of D-arabitol by a newly isolated Zygosaccharomyces rouxii

A newly isolated Zygosaccharomyces rouxii NRRL 27,624 produced D-arabitol as the main metabolic product from glucose. In addition, it also produced ethanol and glycerol. The optimal conditions were temperature 30 degrees C, pH 5.0, 350 rpm, and 5% inoculum. The yeast produced 83.4 +/- 1.1 g D-arabitol from 175 +/- 1.1 g glucose per liter at pH 5.0, 30 degrees C, and 350 rpm in 240 h with a yield of 0.48 g/g glucose. It also produced D-arabitol from fructose, galactose, and mannose. The yeast produced D-arabitol and xylitol from xylose and also from a mixture of xylose and xylulose. Resting yeast cells produced 63.6 +/- 1.9 g D-arabitol from 175 +/- 1.8 g glucose per liter in 210 h at pH 5.0, 30 degrees C and 350 rpm with a yield of 0.36 g/g glucose. The yeast has potential to be used for production of xylitol from glucose via D-arabitol route.

Production of xylitol by metabolically engineered strains of Bacillus subtilis

Xylitol-phosphate dehydrogenase (XPDH) genes from several Gram-positive bacteria were isolated and expressed in Bacillus subtilis. The substrate specificities of the recombinant XPDH enzymes were compared and it was found that the XPDH enzymes of Lactobacillus rhamnosus and Clostridium difficile had the highest selectivity towards D-xylulose 5-phosphate. Expression of these two XPDH enzymes in D-ribulose and D-xylulose producing B. subtilis strain resulted in strains of B. subtilis capable of converting D-glucose into xylitol at around 23% yield.