Search Results (126)

This study aimed to evaluate the production of xylose reductase (XR), an enzyme responsible for converting xylose into xylitol, by Candida tropicalis ATCC 750 using hemicellulosic hydrolysate from cashew apple bagasse (CABHM) as a low-cost carbon source. The effects of temperature, aeration, and fluid dynamics on XR biosynthesis were also investigated. The highest XR production (1.53 U mL⁻¹) was achieved at 30 °C, with 8.3 g·L⁻¹ of xylitol produced by the yeast under microaerobic conditions, demonstrating that aeration and fluid dynamics are important factors in this process. Cellular metabolism and enzyme production decreased at temperatures above 35 °C. The maximum enzymatic activity was observed at pH 7.0 and 50 °C. XR is a heterodimeric protein with a molecular mass of approximately 30 kDa. These results indicate that CABHM is a promising substrate for XR production by C. tropicalis, contributing to the development of enzymatic bioprocesses for xylitol production from lignocellulosic biomass. This study also demonstrates the potential of agro-industrial residues as sustainable feedstocks in biorefineries, aligning with the principles of a circular bioeconomy. Full article

In this study, we established a mouse colitis model using DSS to investigate the impact of curcumin on gut injury, the intestinal microbiota, and fecal metabolites. The findings indicated that curcumin effectively mitigated weight loss and colon shortening caused by colitis, enhanced the expression of anti-inflammatory factor IL-10 mRNA (p < 0.05), and suppressed the expression of pro-inflammatory factors (IL-1β, IL-6, and TNF-α mRNA; p < 0.05). 16S rDNA sequencing analysis showed that in the CUR group, compared to the NC and DSS groups, the abundances of Bacteroides, Lachnospiraceae NK4A136, and Ruminococcaceae UGC 014 significantly increased, while that of Lactobacillus markedly decreased. Additionally, compared with the DSS group, the CUR group demonstrated a significant decrease in levels of metabolites associated with nucleic acid and fat metabolism, including xanthosine, isocitric acid, and D-xylose. Conversely, levels of metabolites of curcumin, such as demethoxycurcumin and tetrahydrocurcumin, were significantly elevated in the CUR group. Curcumin appears to offer protection against mouse colitis by potentially enhancing the composition of the gut microbiota and regulating metabolic and inflammatory processes through its metabolites. Full article

Efficient co-utilization of glucose and xylose from lignocellulosic biomass remains a critical bottleneck limiting the viability of sustainable biorefineries. While Corynebacterium glutamicum has emerged as a promising industrial host due to its robustness, further improvements in mixed-sugar co-utilization are needed. Here, we demonstrate how a single amino acid substitution can dramatically transform cellular sugar transport capacity. By combining rational strain engineering with continuous adaptive laboratory evolution, we evolved a ptsG-deficient C. glutamicum strain in glucose–xylose mixtures for 600 h under consistent selection pressure. Whole-genome sequencing revealed a remarkable finding: a single point mutation; exchanging proline for alanine in the myo-inositol/proton symporter IolT1 was sufficient to boost glucose uptake by 83% and xylose uptake by 20%, while increasing the overall growth rate by 35%. This mutation, located in a highly conserved domain, likely disrupts an alpha helical structure, thus enhancing transport function. Reverse engineering confirmed that this single change alone reproduces the evolved phenotype, representing the first report of an engineered IolT1 variant in PTS-independent C. glutamicum that features significantly enhanced substrate uptake. These results both provide an immediately applicable engineering target for biorefinery applications and demonstrate the power of evolutionary approaches to identify non-intuitive solutions to complex metabolic engineering challenges. Full article

The development of yeast cell factories for efficient xylose utilization and xylitol production is crucial for advancing sustainable biotechnological processes. Xylose, a major component of lignocellulosic biomass, presents challenges for microbial conversion due to its complex metabolic pathways. This study presents the genomic perspective and xylitol production capability of a novel xylose utilizing yeast Cyberlindnera fabianii TBRC 4498. Genome sequencing and functional annotation revealed key metabolic networks and genes involved in the xylose metabolism pathway, providing insights into the strain’s performance. The Cy. fabianii TBRC 4498 had excellent growth and xylose assimilation at a broad range of xylose concentrations from 40 to 140 g/L, with the highest growth rate at 80 g/L of xylose. The highest xylitol production yield (83.19 g/L) was detected from 120 g/L of xylose at 30 °C for 72 h, equivalent to 0.65 g xylitol/g xylose and 1.16 g/L/h productivity. Remarkably, Cy. fabianii TBRC 4498 produced high-purity xylitol, achieving over 95% homogeneity without forming undesirable byproducts, such as acid or ethanol. These results demonstrated the potential of Cy. fabianii TBRC 4498 as a whole-cell biocatalyst for xylitol production using high xylose concentrations, offering a promising microbial cell factory for large-scale xylitol production from lignocellulosic sugar. Full article

Type 2 diabetes, a widespread metabolic disorder, is characterized by hyperglycemia and insulin resistance. Xylose-oligosaccharide, a functional oligosaccharide, has shown potential in mitigating hyperglycemia. This study established a type 2 diabetes mouse model via a high-fat diet and streptozotocin administration to investigate the effects of two xylose-oligosaccharide doses (20 and 60 mg/kg/day). Both doses were observed to regulate lipid metabolism, decrease inflammation, and alleviate damage to the liver, kidneys, and islets. Additionally, xylose-oligosaccharide corrected diabetes-induced intestinal microbiota imbalances by increasing Bacteroides and Proteobacteria while decreasing Firmicutes. Notably, the 60 mg/kg/day dose was more effective in enhancing glucose tolerance and reducing insulin resistance compared to the 20 mg/kg/day dose. These results suggested that xylose-oligosaccharide had hypoglycemic effects, reduced insulin resistance and oxidative stress, possessed anti-inflammatory properties, and modulated intestinal microbiota. Thus, xylose-oligosaccharide shows promise as a functional food for managing type 2 diabetes. Full article

Global warming poses a significant threat to lake ecosystems, with high-mountain lakes being among the earliest and most severely impacted. However, the processes affecting water ecology under climate change remain poorly understood. This study investigates, for the first time, the effects of regional warming on three high-mountain lakes, Sulzata, Okoto and Bubreka, located in the Rila Mountains, Bulgaria, by examining shifts in bacterial metabolic capacity in relation to the rate and range of utilizable carbon sources using the Biolog EcoPlate™ assay. Over the last decade, ice-free water temperatures in the lakes have risen by an average of 2.6 °C, leading to increased nutrient concentrations and enhanced primary productivity, particularly in the shallowest lake. Bacterial communities responded to these changes by increasing their metabolic rates and shifting substrate preferences from carbohydrates to carboxylic acids. While the utilization rates of some carbon sources remained stable, others showed significant changes—some increased (e.g., D-galactonic acid γ-lactone and itaconic acid), while others decreased (e.g., α-D-lactose and D-xylose). The most pronounced effects of warming were observed in June, coinciding with the onset of the growing season. These findings suggest that rising temperatures may substantially alter bacterial metabolic potential, contributing to a long-term positive feedback loop between lake nutrient cycling and climate change. Full article

Ethanol and xylitol are valuable bioproducts synthesized by non-conventional yeasts from lignocellulosic sugars. However, their biosynthesis requires distinct cultivation conditions. This study evaluated the production of ethanol and xylitol by Clavispora lusitaniae using saccharified sugarcane bagasse (SSCB) under three aeration conditions: microaerobic (C1), anaerobic (C2), and a combination of anaerobic followed by a microaerobic phase (C3). Ethanol production was maximum under anaerobic conditions (C2), followed by combined anaerobic–microaerobic conditions (C3). Meanwhile, xylitol production was most efficient under microaerobic conditions (C1). Notably, anaerobic conditions were ineffective for xylitol production. Enzyme activities of xylose reductase (XR) and xylitol dehydrogenase (XDH), key enzymes in xylose metabolism, were highest under microaerobic conditions with activities of 2.88 U/mg and 1.72 U/mg, respectively, after 48 h of culture. Gene expression analysis of XYL1 and XYL2 correlated with the corresponding enzyme activities (XR) and (XDH) with increased levels of 32.38 and 7.88 fold, respectively, compared to the control in C1. These findings suggest that C. lusitaniae co-produces ethanol efficiently under anaerobic conditions, while xylitol biosynthesis is optimized under microaerobic conditions when using xylose-rich saccharified lignocellulosic substrates. Full article

Lactate is a valuable compound used in food, chemical, and pharmaceutical industries. High-value, optically pure L- or D-lactate can be synthesized microbially via specific dehydrogenases. The non-conventional yeast Scheffersomyces stipitis, which is known for fermenting both hexoses and pentoses, is a promising host for biochemical production from lignocellulosic biomass but does not naturally produce lactate. In this study, we engineered S. stipitis to produce lactate by expressing two codon-optimized bacterial L-lactate dehydrogenase genes under the control of strong native promoters. The engineered strain produced 7.42 g/L (0.46 g/g yield) and 11.67 g/L (0.58 g/g yield) lactate from glucose and xylose, respectively. The highest titer, 19.27 g/L (0.52 g/g yield), was achieved from 50 g/L xylose after 74 h. Increasing the fermentation temperature from 28 °C to 32 °C improved yield by 30%, while a neutralizing agent further enhanced yield by 25% and prevented lactate degradation following carbon depletion. Although the wildtype strain produced a significant amount of ethanol on both glucose and xylose, the engineered strain produced ethanol as a side product exclusively on glucose and not on xylose. This phenomenon could be advantageous for biotechnological applications and may reflect shifts in gene expression depending on the carbon source or even on the presence of lactate. Full article

Prebiotics are food ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefits upon host health. Xylooligosaccharides (XOS) are prebiotic fibers made from xylan. Commercial XOS are mixtures of oligosaccharides containing β-1,4–linked xylose residues. Though they are widely added to foods at different doses, the molecular mechanisms of the catabolism and growth promotion of XOS in the innate gut microbes Lactobacillus spp. remain unknown. In this study, we evaluated the growth-promoting effect using a human fecal isolate, Lactiplantibacillus plantarum strain B20 (Lb. plantarum B20). Assays of bacterial growth and lactic acid production showed stronger growth promotion of XOS than other oligosaccharides did, in a dose- and fraction-dependent pattern. Using the Lb. plantarum strain SK151 genome as a reference, bioinformatic analysis failed to identify any previously characterized genes responsible for the uptake and catabolism of XOS. However, transcriptomic analysis of Lb. plantarum B20 yielded numerous differentially expressed genes (DEGs) during fermentation of XOS. Among these, an oligopeptide ABC transporter (RS03575-03595, composed of five proteins) and a hydrolase (RS06170) were significantly upregulated. Molecular docking analysis indicated that the substrate-binding protein RS03575 may mediate the import of XOS into the cell. Enzymatic assays further demonstrated that RS06170 possesses β-xylosidase activity and can effectively degrade XOS. In addition, functional enrichment analysis suggested that the growth-promoting effect of XOS may be attributed to the upregulation of genes involved in cellular component biogenesis and cell division, potentially through modulation of ribosome function and carbohydrate metabolism in Lb. plantarum B20. These results provide valuable insights into the mechanisms by which XOS promote growth and highlight potential targets for enhancing prebiotic–probiotic interactions. Full article

Polygonati Rhizoma, widely used as a traditional functional food and herbal medicine, is well known for its health-promoting activities after the process of “nine cycles of steaming-drying”. Based on UPLC-MS/MS, 1369 secondary metabolites were identified in P. cyrtonema rhizomes, mainly alkaloids, amino acids and derivatives, flavonoids, organic acids, phenolic acids, and saccharides. The P. cyrtonema rhizomes were rich in xylose, arabinose, glucose, sorbose, mannose, galactose, rhamnose, inositol, fucose, sedoheptulose, phosphorylated monosaccharides, sugar acid, and sugar alcohols. Particularly, 23 types of modifications were detected for amino acids, while the most frequent modifications were acetylation, methylation (nono-, di-, and tri-), cyclo-, homo-, and hydroxylation. Based on the metabolic profile, samples from the third cycle (Tre-3) and the sixth cycle (Tre-6) were firstly clustered together due to similar metabolites and then grouped with samples from the ninth cycle (Tre-9). Differentially accumulated metabolites were mainly enriched in “Metabolic pathways”, “Biosynthesis of cofactors”, “Biosynthesis of secondary metabolites”, “Flavonoid biosynthesis”, “Purine metabolism”, “ABC transporters”, “Biosynthesis of amino acids”, and “Nucleotide metabolism” pathways. During repeated steaming–drying processes, 39 metabolites occurred, including alkaloids, amino acids and derivatives, flavonoids, lignans and coumarins, lipids, nucleotides and derivatives, organic acids, phenolic acids, and terpenoids. This research will provide a critical scientific basis for postharvest processing of P. cyrtonema rhizomes. Full article

Efficient co-fermentation of glucose and xylose remains a critical hurdle in second-generation bioethanol production. In this study, we evaluated two non-Saccharomyces yeasts—Wickerhamomyces anomalus UEMG-LF-Y2 and Diutina rugosa UEMG-LF-Y4—under mixed-sugar conditions. D. rugosa exhibited superior xylose metabolism and ethanol productivity, achieving a maximum volumetric productivity (Q_P) of 0.55 g/L·h in a medium containing 20 g/L glucose and 40 g/L xylose. Its highest ethanol yield (Y_P/S) reached 0.45 g EtOH/g sugar, comparable to results from engineered Saccharomyces cerevisiae strains. By contrast, W. anomalus displayed lower ethanol yields (0.24–0.34 g/g) and greater sensitivity to catabolite repression induced by 2-deoxyglucose (2-DG). Xylose consumption by D. rugosa exceeded 80% in high-xylose media, while W. anomalus left residual xylose under all tested conditions. A strong inverse correlation (r < −0.98) between ethanol accumulation and xylose uptake was observed, especially for W. anomalus, indicating ethanol-induced inhibition as a key challenge. These findings highlight the potential of D. rugosa as a robust non-Saccharomyces platform for lignocellulosic bioethanol processes, whereas W. anomalus may benefit from further metabolic or process optimizations. Future research should address ethanol tolerance, inhibitory byproducts, and large-scale feasibility to fully exploit these strains for second-generation bioethanol production. Full article

Bio-based xylonic acid produced from inexpensive lignocellulosic biomass has enormous market potential and enhances the overall economic benefits of biorefinery processes. In this study, the introduction of genes encoding xylose dehydrogenase driven by the promoter Ppdc into Z. mobilis using a plasmid vector resulted in the accumulation of xylonic acid at a titer of 16.8 ± 1.6 g/L. To achieve stable xylonic acid production, a gene cassette for xylonic acid production was integrated into the genome at the chromosomal locus of ZMO0038 and ZMO1650 using the endogenous type I-F CRISPR-Cas system. The titer of the resulting recombinant strain XA3 reduced to 12.2 ± 0.56 g/L, which could be the copy number difference between the plasmid and chromosomal integration. Oxygen content was then identified to be the key factor for xylonic acid production. To further increase xylonic acid production capability, a recombinant strain, XA9, with five copies of a gene cassette for xylonic acid production was constructed by integrating the gene cassette into the genome at the chromosomal locus of ZMO1094, ZMO1547, and ZMO1577 on the basis of XA3. The titer of xylonic acid increased to 51.9 ± 0.1 g/L with a maximum yield of 1.10 g/g, which is close to the theoretical yield in a pure sugar medium. In addition, the recombinant strain XA9 is genetically stable and can produce 16.2 ± 0.14 g/L of xylonic acid with a yield of 1.03 ± 0.01 g/g in the lignocellulosic hydrolysate. Our study thus constructed a recombinant strain, XA9, of Z. mobilis for xylonic acid production from lignocellulosic hydrolysate, demonstrating the capability of Z. mobilis as a biorefinery chassis for economic lignocellulosic biochemical production. Full article

Xylitol is a sugar–alcohol compound with broad applications in fields such as the food, dental, and pharmaceutical sectors. Although xylitol biosynthesis has gained attention, the current strategy for industrial xylitol production majorly relies on the chemical hydrogenation of xylose, which is energy-intensive and environmentally harmful. In this study, the toxicity of xylitol toward Escherichia coli was first examined, and the result demonstrated that Escherichia coli is robust against xylitol at 150 g/L. Genes encoding xylose reductases from different microorganisms were then selected and compared for xylitol production in different E. coli strains. The introduction of xylose reductase of Zymomonas mobilis, driven by the constitutive strong promoter Pgap or Pgap-6M into E. coli, resulted in the accumulation of xylitol at a titer of 64.1 g/L. The increase in NADPH by overexpressing the soluble pyridine nucleotide transhydrogenase encoded by sthA improved the xylitol titer to 83.5 g/L. Seven genes encoding xylose transporters, such as XylE and XylFGH, as well as five mutants of the xylose symporter Glf were then overexpressed and compared for xylitol production. Mutant glf^L445I exhibited the highest improvement in xylitol production at a titer of 88.4 ± 0.7 g/L and a yield of 0.95 g/g. Our study thus demonstrated that xylose reductase derived from Z. mobilis is the best one for xylitol production in E. coli, and xylitol production can be further improved by combining diverse metabolic engineering strategies. Our study, thus, provides efficient xylose reductase and a recombinant strain for future industrial xylitol production. Full article

Concerns over fossil fuels are of increasing interest in biorefineries that utilize lignocellulosic residues. Besides sugars, inhibitors are formed during biomass pretreatment, including acetic acid (AI) and formic acid (FI), which can hinder microbial fermentation. The TG1 and Tuner strains of Escherichia coli were subjected to various acid concentrations. Samples were taken during fermentation to monitor growth, sugar consumption, biomass yield, and product yield. With increasing AI, the TG1 strain maintained stable growth (0.102 1/h), while xylose consumption decreased, and product formation improved, making it better suited for high-acetic-acid industrial applications. In contrast, the Tuner strain performed better under low-inhibitor conditions but suffered metabolic inhibition at high AI levels, compensating by increasing lactic acid production—an adaptation absent in TG1. However, Tuner showed greater resistance to formic acid stress, sustaining higher growth and ethanol production, whereas TG1 experienced a greater metabolic decline but maintained stable acetic acid output. Both strains experienced inhibition in formic acid metabolism, but TG1 had a higher yield despite its lower overall robustness in formic acid conditions. The use of TG1 for value-added compounds such as ethanol or formic acid may help to avoid the use of chemicals that eliminate acetic acid. Tuner could be used for lactic acid production, especially in hydrolysates with under moderate concentration. Full article

The endocarp of Exocarpium Citri Grandis (ECG) is abundant in various bioactive components, such as polysaccharides; however, there are few studies on them. Thus, it is highly necessary to carry out further research on the structural characterization and biological activities of ECG polysaccharides (EPs), which are important bioactive substances. In this study, water-extracted EPs were precipitated by ethanol with final concentrations of 50%, 70%, and 90% (v/v), respectively. Three crude polysaccharides (EP50, EP70, and EP90) were fractioned successively. The three polysaccharide fractions were structurally elucidated and were investigated in vitro for their biological activities related to glucose metabolism containing inhibitory effects on α-glucosidase and non-enzymatic glycosylation and their antioxidant capacities. The main results are summarized as follows: (1) Gradient ethanol precipitation and physicochemical properties of EPs: The yields of EP50, EP70, and EP90 were 11.18%, 0.57%, and 0.18%, respectively. The total sugar contents were 40.01%, 52.61%, and 53.46%, and the uronic acid contents were 30.25%, 18.11%, and 8.17%, respectively. In addition, the three fractions had the same composition of monosaccharides, including rhamnose, arabinose, galactose, glucose, xylose, mannose, galacturonic acid, and glucuronic acid, with differences in the content of neutral and acidic monosaccharides. They all may be branched polymers and spherical conformation, and they were acidic polysaccharides containing esterified and non-esterified uronic acids, pyranose-form sugars, and glycosidic linkages of α-configuration and β-configuration, with esterification degrees of 32.25%, 28.82%, and 15.58%, respectively. Meanwhile, EP50, EP70, and EP90 were mainly amorphous, and the molecular conformation in solution was a spherical branching polymer without a triple helix structure. The EPs exhibited excellent thermal stability, with their structures remaining stable below 170 °C. (2) In terms of activity research, the results showed that EPs had a good α-glucosidase inhibitory effect with IC₅₀ values of 1.17 mg/mL, 1.40 mg/mL, and 2.72 mg/mL, respectively, among which EP50 was the best. EP50, EP70, and EP90 displayed antioxidant activity by scavenging DPPH and ABTS radicals as well as oxygen radical absorbance capacity. Among them, EP90 had the strongest antioxidant activity. Furthermore, the EPs showed prominent effects on the inhibitory activity of non-enzymatic glycosylation. In summary, the research on the extraction of polysaccharide from ECG provides a technical reference for the further utilization of ECG resources. This study on antioxidant activity provides theoretical support for their use as a natural antioxidant. As oxidation and glycation are relevant to diabetic complications, the result of this work suggests that EPs may be effective in preventing and treating diabetic complications. Full article