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Produced by Recombinant Bacteria
Published in Yoshikatsu Murooka, Tadayuki Imanaka, Recombinant Microbes for Industrial and Agricultural Applications, 2020
Xylose isomerase (EC 5.3.1.5) catalyzes the reversible isomerization of D-xylose to D-xylulose in the first step of xylose metabolism following the pentose phosphate cycle. It also catalyzes the isomerization of glucose to fructose and, hence, is used industrially in the production of high-fructose corn syrup (HFCS), under the name glucose isomerase. The enzymes have been isolated from many microorganisms.
Xylitol biosynthesis enhancement by Candida tropicalis via medium, process parameter optimization, and co-substrate supplementation
Published in Preparative Biochemistry & Biotechnology, 2023
Glucose and fructose were consumed preferentially before the xylose during the first 6 h. Subsequently, the xylose uptake rate was lowered, possibly due to the catabolite repression, which may have resulted in lower xylitol yield and productivity. When adding disaccharide sugars (sucrose and maltose), the xylose consumption rate improved because xylose metabolism wasn’t sequential. However, it only resulted in enhanced cell concentration rather than xylitol accumulation, suggesting that most of the xylose used was utilized for cell maintenance. Glycerol offers an efficient and continuous supply of NADH cofactor, as it is a reduced carbon source that can be quickly metabolized compared to conventional ones.[38] Thus, in the present work, its supplementation remarkably improved the xylitol yield and productivity compared to the other co-substrates.
Optimization of co-culture condition with respect to aeration and glucose to xylose ratio for bioethanol production
Published in Indian Chemical Engineer, 2023
Shashi Kumar, G. P. Agarwal, T. R. Sreekrishnan
The P. stipitis monoculture fermentation was investigated to compare the ethanol yield and maximum ethanol production from S. cerevisiae. The fermentation was carried out at an optimal aeration condition of 0.05 vvm and an initial sugar concentration of 30 g/L with a suitable glucose/xylose ratio of 2:1 found in Section 3.1 and Section 3.2. Figure 3 and Table 3: shows that the maximum concentration of ethanol 8.96 ± 0.13 g/L corresponds to an ethanol yield and volumetric productivity of 0.36 g/g and 0.19 g/L/h was found after 48 h of fermentation. The ethanol yield from xylose was only found to be 0.07 g/g xylose, whereas it was of 0.43 g/g glucose from glucose metabolism. The xylose consumption was inferior after the complete utilization of glucose from the fermentation media, which might be resulted due to catabolite repression effect of glucose on P. stipitis on xylose conversion [34]. Catabolite repression effect repress the synthesis of essential enzyme, required for xylose metabolism [6]. Table 3: shows that the ethanol yield (YP/S) obtained from P. stipitis was 79.77% of the ethanol yield of S. cerevisiae using the same synthetic media. Despite the consumption of both sugars, glucose, and xylose by P. stipitis, the resulting yield of ethanol was less compared to the S. cerevisiae.
Optimization of xylitol production from xylose by a novel arabitol limited co-producing Barnettozyma populi NRRL Y-12728
Published in Preparative Biochemistry & Biotechnology, 2021
Badal C. Saha, Gregory J. Kennedy
Microbial production methods offer an alternative that operates under more benign conditions and might be expected to offer better product selectivity. Yeast naturally reduces xylose to xylitol using NADPH-dependent xylose reductase (XR, EC 1.1.1.21), which is the first step in xylose catabolism.[5] Xylitol is often observed to accumulate in the culture because subsequent reactions of xylose metabolism are rate limiting. Arabinose is commonly associated with xylose in hemicellulose. Its presence is problematic because XRs are somewhat promiscuous and will convert it to arabitol.[6] There is no cost-effective process available for separating arabitol from xylitol.