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Submitted to: Current Trends in Microbiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/23/2019 Publication Date: 3/8/2019 Citation: Nichols, N.N., Hector, R.E., Frazer, S.E. 2019. Factors affecting production of xylitol by the furfural-metabolizing fungus Coniochaeta ligniaria. Current Trends in Microbiology. 12: 109-119. Interpretive Summary: Xylitol is a naturally occuring sweetener that has 40% fewer calories than table sugar and has been shown to improve dental health and prevent ear infections. These desirable traits support use of xylitol in pharmaceutical and personal-care products, and as an alternative sweetener in gums and mints. Xylitol is difficult to extract from natural sources; and because the current chemical method of production has high energy and cost demands, a biological route to xylitol is desirable. NCAUR scientists measured the effect of several factors on xylitol production using a microbe that makes xylitol from a sugar, xylose, found in biomass. The microbe has intrinsic resistance to inhibitors of the types encountered in conversion of biomass to fuels and chemicals, and produced up to 0.71 grams of xylitol per gram of xylose. Technical Abstract: Coniochaeta ligniaria (C. ligniaria) C8100 is a xylose non-utilizing mutant derived from wild-type (WT) C. ligniaria NRRL30616. While NRRL30616 metabolizes xylose as a source of carbon and energy, C8100 does not grow on xylose and has reduced xylose reductase (XR) and xylitol dehydrogenase activities compared to WT. Instead, the mutant converts a portion of xylose to xylitol. The use of this mutant strain was investigated to identify culture conditions for increasing xylitol production. Optimal production of xylitol by C. ligniaria occurred at 30-32°C and pH 5-8 in yeast-peptone medium. C8100 produced up to 0.71 g xylitol/g xylose in culture medium and 0.34 g xylitol/g xylose in corn stover dilute acid hydrolysate. As observed in other fungi, productivity (on the order of 0.004 g/L h) was much lower than values reported for yeast. Addition of benzoate to culture medium increased xylitol production. Expression of the Scheffersomyces stipitis XYL1 gene in C. ligniaria C8100 restored XR activity in the mutant to near-WT levels and increased xylitol yield by 20% in rich medium and 11% in corn stover dilute acid hydrolysate. Like the WT strain, C. ligniaria C8100 metabolizes inhibitors in biomass hydrolysates and this inhibitor-tolerant strain may have useful properties for production of xylitol from lignocellulosic biomass. |
