Xylitol production by Cyberlindnera (Williopsis) saturnus , a tropical mangrove yeast from xylose and corn cob hydrolysate

An overview of the metabolically engineered strains and innovative processes used for the value addition of biomass derived xylose to xylitol and xylonic acid

Xylose, the most abundant pentose sugar of the hemicellulosic fraction of lignocellulosic biomass, has to be utilized rationally for the commercial viability of biorefineries. An effective pre-treatment strategy for the release of xylose from the biomass and an appropriate microbe of the status of an Industrial strain for the utilization of this pentose sugar are key challenges which need special attention for the economic success of the biomass value addition to chemicals. Xylitol and xylonic acid, the alcohol and acid derivatives of xylose are highly demanded commodity chemicals globally with plenty of applications in the food and pharma industries. This review emphasis on the natural and metabolically engineered strains utilizing xylose and the progressive and innovative fermentation strategies for the production and subsequent recovery of the above said chemicals from pre-treated biomass medium.

Cyberlindnera dasilvae sp. nov., a xylitol-producing yeast species isolated from rotting wood and frass of cerambycid larva

Six yeast isolates were obtained from rotting wood samples in Brazil and frass of a cerambycid beetle larva in French Guiana. Sequence analysis of the ITS-5.8S region and the D1/D2 domains of the large subunit rRNA gene showed that the isolates represent a novel species of Cyberlindnera. This novel species is related to Cyberlindnera japonica, Cyberlindnera xylosilytica, Candida easanensis and Candida maesa. It is heterothallic and produces asci with two or four hat-shaped ascospores. The name Cyberlindnera dasilvae sp. nov. is proposed to accommodate the novel species. The holotype of Cy. dasilvae is CBS 16129^T and the designated paratype is CBS 16584. The MycoBank number is 838252. All isolates of Cy. dasilvae were able to convert xylose into xylitol with maximum xylitol production within 60 and 72 h. The isolates produced xylitol with values ranging from 12.61 to 31.79 g l^-1 in yeast extract-peptone-xylose medium with 5% xylose. When the isolates were tested in sugarcane bagasse hydrolysate containing around 35-38 g l^-1d-xylose, isolate UFMG-CM-Y519 showed maximum xylitol production.

Xylitol enhances synthesis of propionate in the colon via cross-feeding of gut microbiota

BACKGROUND

Xylitol, a white or transparent polyol or sugar alcohol, is digestible by colonic microorganisms and promotes the proliferation of beneficial bacteria and the production of short-chain fatty acids (SCFAs), but the mechanism underlying these effects remains unknown. We studied mice fed with 0%, 2% (2.17 g/kg/day), or 5% (5.42 g/kg/day) (weight/weight) xylitol in their chow for 3 months. In addition to the in vivo digestion experiments in mice, 3% (weight/volume) (0.27 g/kg/day for a human being) xylitol was added to a colon simulation system (CDMN) for 7 days. We performed 16S rRNA sequencing, beneficial metabolism biomarker quantification, metabolome, and metatranscriptome analyses to investigate the prebiotic mechanism of xylitol. The representative bacteria related to xylitol digestion were selected for single cultivation and co-culture of two and three bacteria to explore the microbial digestion and utilization of xylitol in media with glucose, xylitol, mixed carbon sources, or no-carbon sources. Besides, the mechanisms underlying the shift in the microbial composition and SCFAs were explored in molecular contexts.

RESULTS

In both in vivo and in vitro experiments, we found that xylitol did not significantly influence the structure of the gut microbiome. However, it increased all SCFAs, especially propionate in the lumen and butyrate in the mucosa, with a shift in its corresponding bacteria in vitro. Cross-feeding, a relationship in which one organism consumes metabolites excreted by the other, was observed among Lactobacillus reuteri, Bacteroides fragilis, and Escherichia coli in the utilization of xylitol. At the molecular level, we revealed that xylitol dehydrogenase (EC 1.1.1.14), xylulokinase (EC 2.7.1.17), and xylulose phosphate isomerase (EC 5.1.3.1) were key enzymes in xylitol metabolism and were present in Bacteroides and Lachnospiraceae. Therefore, they are considered keystone bacteria in xylitol digestion. Also, xylitol affected the metabolic pathway of propionate, significantly promoting the transcription of phosphate acetyltransferase (EC 2.3.1.8) in Bifidobacterium and increasing the production of propionate.

CONCLUSIONS

Our results revealed that those key enzymes for xylitol digestion from different bacteria can together support the growth of micro-ecology, but they also enhanced the concentration of propionate, which lowered pH to restrict relative amounts of Escherichia and Staphylococcus. Based on the cross-feeding and competition among those bacteria, xylitol can dynamically balance proportions of the gut microbiome to promote enzymes related to xylitol metabolism and SCFAs. Video Abstract.

Fungi in mangrove ecosystems and their potential applications

Mangrove fungi, their ecological role in mangrove ecosystems, their bioproducts, and potential applications are reviewed in this article. Mangrove ecosystems can play an important role in beach protection, accretion promotion, and sheltering coastlines and creeks as barriers against devastating tropical storms and waves, seawater, and air pollution. The ecosystems are characterized by high average and constant temperatures, high salinity, strong winds, and anaerobic muddy soil. The mangrove ecosystems also provide the unique habitats for the colonization of fungi which can produce different kinds of enzymes for industrial uses, recycling of plants and animals in the ecosystems, and the degradation of pollutants. Many mangrove ecosystem-associated fungi also can produce exopolysaccharides, Ca²⁺-gluconic acid, polymalate, liamocin, polyunsaturated fatty acids, biofuels, xylitol, enzymes, and bioactive substances, which have many potential applications in the bioenergy, food, agricultural, and pharmaceutical industries. Therefore, mangrove ecosystems are rich bioresources for bioindustries and ecology. It is necessary to identify more mangrove fungi and genetically edit them to produce a distinct array of novel chemical entities, enzymes, and bioactive substances.

Production of ethanol and xylanolytic enzymes by yeasts inhabiting rotting wood isolated in sugarcane bagasse hydrolysate

Yeasts associated with rotting wood from four Atlantic Rain forest sites in Brazil were investigated using a culture medium based on sugarcane bagasse hydrolysate. A total of 330 yeast strains were isolated. Pichia manshurica, Candida pseudolambica, and Wickerhamomyces sp. 3 were the most frequently isolated species. Fourteen novel species were obtained in this study. All isolates were tested for their ability to ferment d-xylose and to produce xylanases. In the fermentation assays using d-xylose (30 g L^-1), the main ethanol producers were Scheffersomyces stipitis (14.08 g L^-1), Scheffersomyces sp. (7.94 g L^-1) and Spathaspora boniae (7.16 g L^-1). Sc. stipitis showed the highest ethanol yield (0.42 g g^-1) and the highest productivity (0.39 g L^-1h^-1). The fermentation results using hemicellulosic hydrolysate showed that Sc. stipitis was the best ethanol producer, achieving a yield of 0.32 g g^-1, while Sp. boniae and Scheffersomyces sp. were excellent xylitol producers. The best xylanase-producing yeasts at 50 °C belonged to the species Su. xylanicola (0.487 U mg^-1) and Saitozyma podzolica (0.384 U mg^-1). The results showed that rotting wood collected from the Atlantic Rainforest is a valuable source of yeasts able to grow in sugarcane bagasse hydrolysate, including species with promising biotechnological properties.

Diversity and relationships among strains of culturable yeasts in agricultural soils in Cameroon

Yeasts are unicellular fungi; they are found in a diverse range of natural habitats, including soil, aquatic environments, the surface of plants, and the skin and mucosal surfaces of animal hosts. A variety of yeasts have been found in the soil environment. However, most studies of soil yeasts have come from developed countries, and there is a dearth of research on soil yeasts in Africa. In this study, we analyzed 493 soil samples from nine geographical locations in Cameroon for yeasts, using a culture - based method. A total of 110 yeast isolates were obtained. Based on their sequences at the fungal barcode locus, the Internal Transcribed Spacer (ITS) regions of the nuclear ribosomal RNA gene cluster, the 110 yeast isolates were putatively identified as belonging to 16 yeast species, including 15 Ascomycetes and one Basidiomycete. Differences in yeast species distribution were observed among the analyzed geographic regions. PCR fingerprinting analyses identified a large number of genotypes among strains within each of the obtained yeast species. Significantly, there was little evidence of geographic clustering among yeast strains from any of the yeast species. Our results suggest that Cameroon contains significant yeast diversity and that gene flow is common among local and regional soil yeast populations.

Biochemical Components Associated With Microbial Community Shift During the Pile-Fermentation of Primary Dark Tea

Primary dark tea is used as raw material for compressed dark tea, such as Fu brick tea, Hei brick tea, Hua brick tea, and Qianliang tea. Pile-fermentation is the key process for the formation of the characteristic properties of primary dark tea, during which the microorganism plays an important role. In this study, the changes of major chemical compounds, enzyme activities, microbial diversity, and their correlations were explored during the pile-fermentation process. Our chemical and enzymatic analysis showed that the contents of the major compounds were decreased, while the activities of polyphenol oxidase, cellulase, and pectinase were increased during this process, except peroxidase activity that could not be generated from microbial communities in primary dark tea. The genera Cyberlindnera, Aspergillus, Uwebraunia, and Unclassified Pleosporales of fungus and Klebsiella, Lactobacillus of bacteria were predominant in the early stage of the process, but only Cyberlindnera and Klebsiella were still dominated in the late stage and maintained a relatively constant until the end of the process. The amino acid was identified as the important abiotic factor in shaping the microbial community structure of primary dark tea ecosystem. Network analysis revealed that the microbial taxa were grouped into five modules and seven keystone taxa were identified. Most of the dominant genera were mainly distributed into module III, which indicated that this module was important for the pile-fermentation process of primary dark tea. In addition, bidirectional orthogonal partial least squares (O2PLS) analysis revealed that the fungi made more contributions to the formation of the characteristic properties of primary dark tea than bacteria during the pile-fermentation process. Furthermore, 10 microbial genera including Cyberlindnera, Aspergillus, Eurotium, Uwebraunia, Debaryomyces, Lophiostoma, Peltaster, Klebsiella, Aurantimonas, and Methylobacterium were identified as core functional genera for the pile-fermentation of primary dark tea. This study provides useful information for improving our understanding on the formation mechanism of the characteristic properties of primary dark tea during the pile-fermentation process.

Lipid production and characterization by Mortierella (Umbelopsis) isabellina cultivated on lignocellulosic sugars

AIMS

To study and characterize the lipids produced by Mortierella (Umbelopsis) isabellina, during its growth on mixtures of glucose and xylose.

METHODS AND RESULTS

Glucose and xylose were utilized as carbon sources, solely or in blends, under nitrogen-limited conditions, in batch-flask trials (initial sugars at 80 g l^-1 ). Significant lipid production (maximum lipid 17·8 g l^-1 ; lipid in DCW 61·0% w/w; lipid on glucose consumed 0·23 g g^-1 ) occurred on glucose employed solely, while xylose concentration in the growth medium was conversely correlated with lipid accumulation. With increasing xylose concentrations into the blend, lipid storage decreased while xylitol in significant concentrations (up to 24 g l^-1 ) was produced. Irrespective of the sugar blend employed, significant quantities of endopolysaccharides were detected in the first growth steps (in the presence of nitrogen into the medium or barely after its disappearance) while lipids were stored thereafter. Neutral lipids, mainly composed of triacylglycerols, were the main microbial lipid fraction. Phospholipids were quantified both through fractionation and subsequent gravimetric determination and also through determination of phosphorus, and it seemed that the second method was more accurate. Phospholipids were mainly composed of phosphatidylcholine and another nonidentified compound presumably being phosphatidyldimethylethanolamine.

CONCLUSIONS

Mortierella isabellina is suitable to convert lignocellulosic sugars into lipids.

SIGNIFICANCE AND IMPACT OF THE STUDY

Differentiations between metabolism on xylose and glucose were reported. Moreover, this is one of the first reports indicating extensive analysis of microbial lipids produced by M. isabellina.

Relationship between salt tolerance and nanoparticle synthesis by Williopsis saturnus NCIM 3298

This work describes cell associated and extracellular synthesis of nanoparticles by the yeast, Williopsis saturnus. The yeast was able to grow in the absence and presence of sodium chloride (NaCl) and form nanoparticles in a cell associated manner. The content of melanin, a stress-associated pigment was found to be progressively greater in the presence of increasing concentrations of NaCl. With higher quantities of melanin (extracted from yeast cells grown in the presence of 4% of NaCl), smaller sized nanoparticles were obtained. This is the first report on understanding the relationship between halotolerance, production of a stress-related pigment (melanin) and synthesis of nanoparticles with antioxidant properties by using W. saturnus as a model system. The cell free extracts derived from cultures grown in the absence of NaCl were able to mediate extracellular synthesis of gold and silver nanoparticles and the biomolecule mediating nanoparticle synthesis was identified to be a glycolipid. Extracellularly synthesized gold nanoparticles displayed good catalytic activity and rapidly mediated the reduction of 4-nitrophenol to 4-aminophenol.

Evaluation of some lignocellulosic byproducts of food industry for microbial xylitol production by Candida tropicalis

Some lignocellulosic food byproducts such as potato peels, wheat bran, barley bran and chestnut shells were evaluated as potential sources of xylose for microbial xylitol production by yeasts. Potential yeast strains were selected after screening xylitol production of some indigenous yeasts in a defined fermentation medium. Candida tropicalis strains gave the highest results with 83.28 and 54.07 g/L xylitol production from 100 g/L xylose. Lignocellulosic materials were exposed to acid hydrolysis at different conditions. Chestnut shells gave the highest xylose yield and the hydrolysate of chestnut shells was used in further experiments in which xylitol productions of two potential C. tropicalis strains were investigated. Combined detoxification method including evaporation, overliming and activated charcoal with the use of threefold concentration and also yeast extract supplementation suggested to be efficient for both growth and product formation in chestnut shell hydrolysate in which 40 % xylitol yield was obtained. It was concluded that detoxified and fortified chestnut shell hydrolysate could be a potential medium for xylitol production.

Bio-products produced by marine yeasts and their potential applications

It has been well documented that the yeasts isolated from different marine environments are so versatile that they can produce various fine chemicals, enzymes, bioactive substances, single cell protein and nanoparticles. Many genes related to the biosynthesis and regulation of these functional biomolecules have been cloned, expressed and characterized. All these functional biomolecules have a variety of applications in industries of food, chemical, agricultural, biofuel, cosmetics and pharmacy. In this review, a summary will be given about these functional biomolecules and their producers of the marine yeasts as well as some related genes in order to draw an outline about necessity for further exploitation of marine yeasts and their bio-products for industrial applications.

Cyberlindnera xylosilytica sp. nov., a xylitol-producing yeast species isolated from lignocellulosic materials

Independent surveys of yeasts associated with lignocellulosic-related materials led to the discovery of a novel yeast species belonging to the Cyberlindnera clade (Saccharomycotina, Ascomycota). Analysis of the sequences of the internal transcribed spacer (ITS) region and the D1/D2 domains of the large subunit rRNA gene showed that this species is related to C. japonica, C. maesa and C. easanensis. Six isolates were obtained from different sources, including rotting wood, tree bark and sugar cane filter cake in Brazil, frass from white oak in the USA and decayed leaf in Taiwan. A novel species is suggested to accommodate these isolates, for which the name C. xylosilytica sp. nov. is proposed. The type strain of C. xylosilytica sp. nov. is NRRL YB-2097(T) ( = CBS 13984(T) = UFMG-CM-Y347(T)) and the allotype is UFMG-CM-Y409 ( = CBS 14083). The novel species is heterothallic and complementary mating types are represented by the type and allotype strains. The MycoBank number is MB 811428.