Production of arabitol by yeasts: current status and future prospects

Diversity, Distribution, and Phenotypic Characterization of Cultivable Wild Yeasts Isolated from Natural Forest

Background

Yeasts are unicellular fungi that inhabit a variety of environments including plant surfaces, water, soil, and animal hosts. However, limited research has been conducted on soil and plant associated yeasts in Africa, with most studies originating from developed regions.

Methods

This study explored the diversity, distribution, and phenotypic characterization of cultivable wild yeast in samples from rhizosphere soil, leaves, litter, and tree bark collected from South West Ethiopia. Yeast isolates were characterized using morphological, physiological and biochemical methods, Stress-tolerant yeast species were identified using Matrix-Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF).

Results

Based on morphological, physiological, and biochemical analyses, a total of 15 yeast genera were identified from 23 plant species. Predominant yeast species included Candida spp., Saccharomyces spp., Meyerozyma spp., Pichia spp., Geotrichum spp., and Hanseniaspora spp. Plant species with the highest yeast diversity were Ficus vasta, Ficus exasperata, Ficus sycomorus, Cordia africana, and Ritchiea albersii. Bark samples yielded more yeast isolates than rhizosphere soil, litter, and leaves. Stress-tolerant species such as Saccharomyces cerevisiae, Candida pelliculosa, Meyerozyma guilliermondii, Pichia kluyveri, and Trichosporon asahii were identified using MALDI-TOF. Correlation analysis revealed no significant relationship between yeast populations in bark and leaf samples or between rhizosphere soil and leaves, though a weak positive correlation was found between rhizosphere soil and bark or litter. Seasonal analysis showed a strong positive correlation between yeast abundance in spring and summer, but no association between autumn and spring.

Conclusion

Ethiopian forests are home for various yeast species including the stress-tolerant wild yeasts. This study highlights the significant yeast diversity in Ethiopian forests, with potential applications in improving industrial fermentation processes that operate under stressful conditions.

Effect of Dietary Addition of Lentinus edodes on Rumen Flora, Lactation, and Health of Dairy Goats

Lentinus edodes (LE) is a nutrient-rich medicinal fungus with potential applications in animal nutrition; however, its effects on dairy goats remain underexplored. This study investigated the impact of dietary LE addition on rumen microbiota, metabolic profiles, serum immunity, and milk quality in lactating dairy goats. Twenty Saanen goats were randomly assigned to a control group (CON, basal diet) or an LE group (basal diet + 25 g Lentinus edodes) for 56 days. Rumen fluid, serum, and milk samples were analyzed using 16S rDNA sequencing, metabolomics, and biochemical assays. The results showed that the addition of LE altered the microbial composition, decreasing the abundance of fibrobacterial flora and Treponema (p < 0.05) while increasing VadinHA49. Metabolomic analysis revealed elevated fumaric acid, lysophospholipids (LysoPE, LysoPG), and D-quinic acid in the rumen (p < 0.05). Serum immunoglobulin A (IgA), immunoglobulin G (IgG), total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), and tumor necrosis factor-α (TNF-α) levels were significantly enhanced (p < 0.05). The milk somatic cell count (SCC) was reduced by 52.8% (p = 0.005) at day 56, and protein, fat, and total solids increased significantly (p < 0.05). Enrichment of functional metabolites such as D-arabitol and D-tryptophan in milk further highlighted LE's role in improving product value. These findings demonstrate that LE optimizes rumen flora, enhances antioxidant and immune functions, and improves milk quality, supporting its use as a functional feed additive for dairy goats.

Early-life gut mycobiome core species modulate metabolic health in mice

The gut microbiome causally contributes to obesity; however, the role of fungi remains understudied. We previously identified three core species of the infant gut mycobiome (Rhodotorula mucilaginosa, Malassezia restricta and Candida albicans) that correlated with body mass index, however their causal contributions to obesity development are unknown. Here we show the effects of early-life colonization by these fungal species on metabolic health in gnotobiotic mice fed standard (SD) or high-fat-high-sucrose (HFHS) diets. Each species resulted in bacterial microbiome compositional and functional differences. R. mucilaginosa and M. restricta increased adiposity in mice fed SD, while only R. mucilaginosa exacerbated metabolic disease. In contrast, C. albicans resulted in leanness and resistance to diet-induced obesity. Intestinal nutrient transporter expression was unaffected by the presence of fungi in jejunal enteroids, yet the immune landscape in white adipose tissue was distinctly impacted by each fungal species, suggesting that these phenotypes may be a result of fungal immune regulation. This work revealed that three common fungal colonizers have distinct causal influences on obesity and metabolic inflammation and justifies the consideration of fungi in microbiome research on host metabolism.

Phytochemicals that Regulate Oviposition Mistakes of Eurema mandarina on Oxalis corniculata

Eurema mandarina is a pierid butterfly that primarily feeds on plants in the family Fabaceae. In mainland Japan, adult females preferentially lay eggs on Albizia julibrissin and Lespedeza cuneata. In the field, females may oviposit on non-fabaceous plants, although rarely. When maintained in our laboratory with their natural hosts removed, females showed moderate oviposition responses to Oxalis corniculata (Oxalidaceae), but newly hatched larvae failed to grow to the second instar on the leaves. This indicated that females made oviposition mistakes on O. corniculata because it is not suitable for larval development. We attempted to identify the phytochemicals that regulate oviposition of E. mandarina on O. corniculata. Females hardly responded to the methanolic leaf extract and its aqueous fraction but responded weakly to the most polar subfraction. Further fractionation of this subfraction by ion-exchange column chromatography revealed high oviposition-eliciting activity in the acidic subfraction and low activity in the acidic/neutral/amphoteric and neutral/amphoteric subfractions. Mass spectrometry and oviposition bioassays identified erythronic and threonic acids as stimulants in the acidic subfraction, and arabinose and arabitol as deterrents in the neutral/amphoteric subfraction. Leaf samples of O. corniculata varied greatly in the composition of the four components; however, none contained the concentration of stimulants necessary to induce oviposition without being counteracted by deterrents. These results suggest that oviposition mistakes on O. corniculata, though infrequently, occur when females discover non-hosts with sufficiently high concentrations of stimulants and sufficiently low concentrations of deterrents.

Renal Sugar Metabolites and mRNA Expression of Glucose Transporters in Meat-Type Chickens with Differing Residual Water Intake

Molecular differences exist between birds with high residual water intake (HRWI) compared to those with low residual water intake (LRWI). Residual water intake (RWI) is defined as the difference between the water intake of a bird and the expected water intake corrected for metabolic body weight, feed intake, and body weight gain. Tissue metabolomic analysis revealed significantly increased kidney glucose, fructose, and arabitol in the LRWI group compared to the HRWI group. mRNA expression analysis of apical sodium glucose cotransporters SGLT1, SGLT4, SGLT5, and SGLT6 showed decreased expression of SGLTs 1, 5, and 6 in LRWI birds (p < 0.05), whereas SGLT4 expression was increased compared with HRWI birds (p < 0.01). An analysis of basal glucose transporters GLUT1, GLUT2, GLUT5, and GLUT9 showed significantly increased GLUT2 expression in LRWI birds compared with HRWI birds (p < 0.01). We postulate that SGLT4 is the main apical transporter in chicken kidneys and that its increased expression reduces these birds' need for water, resulting in less drinking. This is balanced by the increased expression of the basal transporter GLUT2, indicating better glucose retention, which may partly explain the physiological mechanism behind why these birds drink less water. Innately driven broiler water intake could therefore be influenced by the expression of kidney solute transporters.

Exploring the Impact of Solid-State Fermentation on Fava Bean Flour: A Comparative Study of Aspergillus oryzae and Rhizopus oligosporus

Fava bean (Vicia faba L.) is a protein-rich pulse with high nutritional value, but its functional and sensory characteristics limit its application in foods. Solid-state fermentation (SSF) can modify the composition of plant proteins, modulate its functionality, and enhance the sensory aspects. In this study, fava bean flour (FB) was fermented with Aspergillus oryzae and Rhizopus oligosporus to produce FBA and FBR, respectively, ingredients with distinct nutritional, functional, and aroma characteristics. The protein content increased by 20% in FBA and 8% in FBR, while fat levels rose more significantly in FBR (+40%). The overall content of fermentable oligo-, di-, mono-saccharides, and polyols (FODMAPs) decreased by 47% (FBA) and 57% (FBR), although polyol production by A. oryzae was observed. SSF improved the nutritional profile of FBA and FBR, with a notable increase in the concentration of essential amino acids observed, and a reduction in most antinutrients, with the exception of trypsin inhibitors. SSF resulted in the formation of aggregates, which increased the particle size and reduced protein solubility. Emulsions prepared with the fermented ingredients separated faster, and the foaming capacity of both FBA and FBR was decreased, but an increase in water-holding capacity was observed. SSF resulted in the production of predominantly savoury-associated aroma compounds, with compounds characteristic of metallic and mouldy aromas reduced. These results indicate the potential of SSF to transform FB with enhanced nutritional value and improved sensory and functional properties.

Isolation, screening, and characterization of the newly isolated osmotolerant yeast Wickerhamomyces anomalus BKK11-4 for the coproduction of glycerol and arabitol

This study explored the isolation and screening of an osmotolerant yeast, Wickerhamomyces anomalus BKK11-4, which is proficient in utilizing renewable feedstocks for sugar alcohol production. In batch fermentation with high initial glucose concentrations, W. anomalus BKK11-4 exhibited notable production of glycerol and arabitol. The results of the medium optimization experiments revealed that trace elements, such as H3BO3, CuSO4, FeCl3, MnSO4, KI, H4MoNa2O4, and ZnSO4, did not increase glucose consumption or sugar alcohol production but substantially increased cell biomass. Osmotic stress, which was manipulated by varying initial glucose concentrations, influenced metabolic outcomes. Elevated glucose levels promoted glycerol and arabitol production while decreasing citric acid production. Agitation rates significantly impacted the kinetics, enhancing glucose utilization and metabolite production rates, particularly for glycerol, arabitol, and citric acid. The operational pH dictated the distribution of the end metabolites, with glycerol production slightly reduced at pH 6, while arabitol production remained unaffected. Citric acid production was observed at pH 6 and 7, and acetic acid production was observed at pH 7. Metabolomic analysis using GC/MS identified 29 metabolites, emphasizing the abundance of sugar/sugar alcohols. Heatmaps were generated to depict the variations in metabolite levels under different osmotic stress conditions, highlighting the intricate metabolic dynamics occurring post-glucose uptake, affecting pathways such as the pentose phosphate pathway and glycerolipid metabolism. These insights contribute to the optimization of W. anomalus BKK11-4 as a whole-cell factory for desirable products, demonstrating its potential applicability in sustainable sugar alcohol production from renewable feedstocks.

Arabinose as an overlooked sugar for microbial bioproduction of chemical building blocks

The circular economy is anticipated to bring a disruptive transformation in manufacturing technologies. Robust and industrial scalable microbial strains that can simultaneously assimilate and valorize multiple carbon substrates are highly desirable, as waste bioresources contain substantial amounts of renewable and fermentable carbon, which is diverse. Lignocellulosic biomass (LCB) is identified as an inexhaustible and alternative resource to reduce global dependence on oil. Glucose, xylose, and arabinose are the major monomeric sugars in LCB. However, primary research has focused on the use of glucose. On the other hand, the valorization of pentose sugars, xylose, and arabinose, has been mainly overlooked, despite possible assimilation by vast microbial communities. The present review highlights the research efforts that have explicitly proven the suitability of arabinose as the starting feedstock for producing various chemical building blocks via biological routes. It begins by analyzing the availability of various arabinose-rich biorenewable sources that can serve as potential feedstocks for biorefineries. The subsequent section outlines the current understanding of arabinose metabolism, biochemical routes prevalent in prokaryotic and eukaryotic systems, and possible products that can be derived from this sugar. Further, currently, exemplar products from arabinose, including arabitol, 2,3-butanediol, 1,2,3-butanetriol, ethanol, lactic acid, and xylitol are discussed, which have been produced by native and non-native microbial strains using metabolic engineering and genome editing tools. The final section deals with the challenges and obstacles associated with arabinose-based production, followed by concluding remarks and prospects.

d-Arabitol production by a high arabitol-producing yeast, Zygosaccharomyces sp. Gz-5 isolated from miso

d-Arabitol, an alternative sweetener to sugar, has low calorie content, high sweetness, low glycemic index, and insulin resistance-improving ability. In this study, d-arabitol-producing yeast strains were isolated from various commercial types of miso, and strain Gz-5 was selected among these strains. Phylogenetic tree analysis of the internal transcribed spacer sequence revealed that strain Gz-5 was distinct from Zygosaccharomyces rouxii, a major fermenting yeast of miso. The strain, identified as Zygosaccharomyces sp. Gz-5, grew better than other Z. rouxii in 150 g/L NaCl and produced 114 g/L d-arabitol from 295 g/L glucose in a batch culture for 8 days (0.386 g/g-consumed glucose). In a fed-batch culture, the yeast produced 133 g/L d-arabitol for 14 days, and the total d-arabitol amount increased by 1.75-fold. These results indicated that Zygosaccharomyces sp. Gz-5, a non-genetically modified strain, has excellent potential for the industrial production of d-arabitol.

Analysis of the Correlation between Persimmon Fruit-Sugar Components and Taste Traits from Germplasm Evaluation

Persimmon fruits are brightly colored and nutritious and are fruits that contain large amounts of sugar, vitamins, mineral elements, and phenolic substances. The aim of this study was to explore the differences in fruit-sugar components of different persimmon germplasms and their relationships with phenotypic and flavor indices through the determination of phenotypes and sugar components and through electronic-tongue indices, which provided the basis and inspiration for the selection of different sugar-accumulating types of persimmon fruits and the selection of high-sugar persimmon varieties. Our results showed that persimmon germplasm fruit-sugar components were dominated by sucrose, glucose and fructose and that the remaining sugar components were more diverse but less distributed among the various germplasm types. Based on the proportion of each sugar component in the fruit, persimmon germplasms can be categorized into sucrose-accumulating and reduced-sugar-accumulation types. Sucrose-accumulating types are dominated by sucrose, galactose, fucose and inositol, while reduced-sugar-accumulation types are dominated by glucose, fructose, mannose-6-phosphate, and xylose. The content of sugar components in the germplasm persimmon of fruits of different types and maturity periods of also differed, with significant differences in sugar components between PCNA (pollination-constant non-astringent) and PCA (pollination-constant astringent) fruits. Cluster analysis classified 81 persimmon germplasms into three clusters, including cluster I-A, with low glucose and fructose content, and cluster I-B, with medium glucose, fructose, and sucrose contents. Cluster II was high in sucrose and fructose. Cluster III had high contents of glucose and fructose and low contents of sucrose and inositol.

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.

Production of arabitol from glycerol by immobilized cells of Wickerhamomyces anomalus WC 1501

Polyalcohols such as arabitol are among the main targets of biorefineries aiming to upcycle wastes and cheap substrates. In previous works Wickerhamomyces anomalus WC 1501 emerged as an excellent arabitol producer utilizing glycerol. Arabitol production by this strain is not growth associated, therefore, in this study, pre-grown cells were entrapped in calcium alginate beads (AB) and utilized for glycerol transformation to arabitol. Flasks experiments aimed to assess the medium composition (i.e., the concentration of inorganic and organic nitrogen sources and phosphates) and to establish the appropriate carrier-to-medium proportion. In flasks, under the best conditions of ammonium limitation and the carrier:medium ratio of 1:3 (w/v), 82.7 g/L glycerol were consumed in 168 h, yielding 31.2 g/L arabitol, with a conversion of 38% and volumetric productivity of 186 mg/mL/h. The process with immobilized cells was transferred to laboratory scale bioreactors with different configurations: stirred tank (STR), packed bed (PBR), fluidized bed (FBR), and airlift (ALR) bioreactors. The STR experienced oxygen limitation due to the need to maintain low stirring to preserve AB integrity and performed worse than flasks. Limitations in diffusion and mass transfer of oxygen and/or nutrients characterized also the PBR and the FBR and were partially relieved only in ALR, where 89.4 g/L glycerol were consumed in 168 h, yielding 38.1 g/L arabitol, with a conversion of 42% and volumetric productivity of 227 mg/mL/h. When the ALR was supplied with successive pulses of concentrated glycerol to replenish the glycerol as it was being consumed, 117 g/L arabitol were generated in 500 h, consuming a total of 285 g/L glycerol, with a 41% and 234 mg/L/h. The study strongly supports the potential of W. anomalus WC 1501 for efficient glycerol-to-arabitol conversion using immobilized cells. While the yeast shows promise by remaining viable and active for extended periods, further optimization is required, especially regarding mixing and oxygenation. Improving the stability of the immobilization process is also crucial for reusing pre-grown cells in multiple cycles, reducing dead times, biomass production costs, and enhancing the economic feasibility of the process.

Screening of Secondary Metabolites Produced by Nigrospora sphaerica Associated with the Invasive Weed Cenchrus ciliaris Reveals Two New Structurally Related Compounds

In the search for new alternative biocontrol strategies, phytopathogenic fungi could represent a new frontier for weed management. In this respect, as part of our ongoing work aiming at using fungal pathogens as an alternative to common herbicides, the foliar pathogen Nigrospora sphaerica has been evaluated to control buffelgrass (Cenchrus ciliaris). In particular, in this work, the isolation and structural elucidation of two new biosynthetically related metabolites, named nigrosphaeritriol (3-(hydroxymethyl)-2-methylpentane-1,4-diol) and nigrosphaerilactol (3-(1-hydroxyethyl)-4-methyltetrahydrofuran-2-ol), from the phytotoxic culture filtrate extract were described, along with the identification of several known metabolites. Moreover, the absolute stereochemistry of (3R,4S,5S)-nigrosphaerilactone, previously reported as (3S,4R,5R)-4-hydroxymethyl-3,5-dimethyldihydro-2-furanone, was determined for the first time by X-ray diffraction analysis. Considering their structural relationship, the determination of the absolute stereochemistry of nigrosphaerilactone allowed us to hypothesize the absolute stereochemistry of nigrosphaeritriol and nigrosphaerilactol.

Preliminary Findings on the Salivary Metabolome of Hookah and Cigarette Smokers

The aim of the study was to evaluate the salivary metabolomic profile of patients who habitually smoke hookah and cigarettes. The groups consisted of 33 regular and exclusive hookah smokers, 26 regular and exclusive cigarette smokers, and 30 nonsmokers. Unstimulated whole saliva was collected for the measurement of salivary metabolites by gas chromatography coupled with tandem mass spectrometry (GC-MS/MS). The MetaboAnalyst software was used for statistical analysis and evaluation of biomarkers. 11 smoking salivary biomarkers were identified using the area under receiving-operator curver criterion and threshold of 0.9. Xylitol and octadecanol were higher in cigarette smokers compared to controls; arabitol and maltose were higher in controls compared to cigarette smokers; octadecanol and tyramine were higher in hookah smokers compared to controls; phenylalanine was higher in controls compared to hookah smokers; and fructose, isocitric acid, glucuronic acid, tryptamine, maltose, tyramine, and 3-hydroxyisolvaleric acid were higher in hookah smokers compared to cigarettes smokers. Conclusions: The evaluation of the salivary metabolome of hookah smokers, showing separation between the groups, especially between the control versus hookah groups and cigarette versus hookah groups, and it seems to demonstrate that the use of hookah tobacco is more damaging to health.

Non-canonical D-xylose and L-arabinose metabolism via D-arabitol in the oleaginous yeast Rhodosporidium toruloides

R. toruloides is an oleaginous yeast, with diverse metabolic capacities and high tolerance for inhibitory compounds abundant in plant biomass hydrolysates. While R. toruloides grows on several pentose sugars and alcohols, further engineering of the native pathway is required for efficient conversion of biomass-derived sugars to higher value bioproducts. A previous high-throughput study inferred that R. toruloides possesses a non-canonical L-arabinose and D-xylose metabolism proceeding through D-arabitol and D-ribulose. In this study, we present a combination of genetic and metabolite data that refine and extend that model. Chiral separations definitively illustrate that D-arabitol is the enantiomer that accumulates under pentose metabolism. Deletion of putative D-arabitol-2-dehydrogenase (RTO4_9990) results in > 75% conversion of D-xylose to D-arabitol, and is growth-complemented on pentoses by heterologous xylulose kinase expression. Deletion of putative D-ribulose kinase (RTO4_14368) arrests all growth on any pentose tested. Analysis of several pentose dehydrogenase mutants elucidates a complex pathway with multiple enzymes mediating multiple different reactions in differing combinations, from which we also inferred a putative L-ribulose utilization pathway. Our results suggest that we have identified enzymes responsible for the majority of pathway flux, with additional unknown enzymes providing accessory activity at multiple steps. Further biochemical characterization of the enzymes described here will enable a more complete and quantitative understanding of R. toruloides pentose metabolism. These findings add to a growing understanding of the diversity and complexity of microbial pentose metabolism.

Comparison of the Main Constituents in Two Varieties of Proso Millet Using GC-MS

Proso millet (Panicum miliaceum) is neglected in human nutrition. Thanks to the composition of the grains, millet is suitable for people with celiac disease and it is also useful in the prevention of cardiovascular diseases. For screening the substances in all plant parts of millet via GC-MS, two varieties, Hanacká Mana and Unicum, were used. Substances from the group saccharides, amino acids, fatty acids, carboxylic acids, phytosterols and others were identified in the roots, leaves, stems, and seeds. The highest level of saccharides was found in the stems (83%); amino acids in the roots (6.9%); fatty acids in the seeds (24.6%); carboxylic acids in the roots (3%), phytosterols in the seeds (10.51%); other substances, such as tetramethyl-2-hexadecenol (1.84%) and tocopherols (2.15%), in the leaves; retinal in the roots (1.30%) and squalene in the seeds (1.29%). Saccharides were the dominant group in all plant parts of proso millet followed by fatty acids. The dominant saccharides in all parts of the millet plant were sucrose, fructose and psicose. On the contrary, turanose, trehalose, glucose and cellobiose belonged to the least represented sugars. Additionally, amyrin, miliacin, campesterol, stigmasterol, β-sitosterol, and others were identified. Varietal variability can be assumed, e.g., in retinal, miliacin or amyrin content.

Comparison of Phenolic and Volatile Compounds in MD2 Pineapple Peel and Core

The peel and core discarded from the processing of MD2 pineapple have the potential to be valorized. This study evaluated the functional and volatile compounds in the extracts of MD pineapple peel and core (MD2-PPC). The total soluble solids, pH, titratable acidity, sweetness index, and astringency index were 9.34 °Brix, 4.00, 0.74%, 12.84, and 0.08, respectively, for the peel and 12.00 °Brix, 3.96, 0.32%, 37.66, and 0.03, respectively, for the core. The fat and protein contents of the peel and core were found to be significantly different (p < 0.05). The total phenolic (TPC) and flavonoid contents (TFC) were significantly higher in the peel. The peel also showed better antioxidant activity, with a half-maximal inhibitory concentration (IC₅₀) of 0.63 mg/mL for DPPH free radical activity compared with the core. The TPC of different phenolic fractions from peel extract was highest in the glycosylated fraction, followed by the esterified, insoluble-bound, and free phenolic fractions. GC-MS analysis identified 38 compounds in the peel and 23 in the core. The primary volatile compounds were 2-furan carboxaldehyde, 5-(hydroxymethyl), and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP). The identification of phenolics and volatile compounds provides important insights into the valorization of (MD2-PPC) waste.

Identification of an l-Arabitol Transporter from Aspergillus niger

l-arabitol is an intermediate of the pentose catabolic pathway in fungi but can also be used as a carbon source by many fungi, suggesting the presence of transporters for this polyol. In this study, an l-arabitol transporter, LatA, was identified in Aspergillus niger. Growth and expression profiles as well as sugar consumption analysis indicated that LatA only imports l-arabitol and is regulated by the arabinanolytic transcriptional activator AraR. Moreover, l-arabitol production from wheat bran was increased in a metabolically engineered A. niger mutant by the deletion of latA, indicating its potential for improving l-arabitol-producing cell factories. Phylogenetic analysis showed that homologs of LatA are widely conserved in fungi.

d-Arabitol Ameliorates Obesity and Metabolic Disorders via the Gut Microbiota-SCFAs-WAT Browning Axis

d-Arabitol, which is typically found in mushrooms, lichens, and higher fungi, might play an effective role in alleviating visceral fat accumulation and insulin resistance particularly for its low calorie and glycemic index. However, the regulatory mechanisms of d-arabitol for alleviating obesity and associated metabolic disorders remain poorly understood. This study aimed to investigate and analyze the underlying relationship between d-arabitol-mediated gut microbiota and obesity. The results showed that d-arabitol dramatically ameliorated body weight gain, fat accumulation, and insulin resistance in HFD-fed rats. Likewise, d-arabitol remarkably increased the relative abundance of the genera Blautia, Anaerostipes, and Phascolarctobacterium and decreased the genera Romboutsia and Clostridium_sensu_stricto_1. Furthermore, these alterations in gut microflora increased SCFAs, which in turn indirectly promoted AMPK-PGC-1α-related white adipose tissue (WAT) browning. Therefore, d-arabitol would have the potential to alleviate obesity through the gut microbiota-SCFAs-WAT browning axis. It could be considered as a sugar substitute for the obese population and diabetic patients.

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.

Improved fed-batch processes with Wickerhamomyces anomalus WC 1501 for the production of D-arabitol from pure glycerol

BACKGROUND

D-Arabitol, a five-carbon sugar alcohol, represents a main target of microbial biorefineries aiming to valorize cheap substrates. The yeast Wickerhamomyces anomalus WC 1501 is known to produce arabitol in a glycerol-based nitrogen-limited medium and preliminary fed-batch processes with this yeast were reported to yield 18.0 g/L arabitol.

RESULTS

Fed-batch fermentations with W. anomalus WC 1501 were optimized using central composite design (CCD). Dissolved oxygen had not a significant effect, while optimum values were found for glycerol concentration (114.5 g/L), pH (5.9), and temperature (32.5 °C), yielding 29 g/L D-arabitol in 160 h, a conversion yield of 0.25 g of arabitol per g of consumed glycerol, and a volumetric productivity of 0.18 g/L/h. CCD optimal conditions were the basis for further improvement, consisting in increasing the cellular density (3✕), applying a constant feeding of glycerol, and increasing temperature during production. The best performing fed-batch fermentations achieved 265 g/L D-arabitol after 325 h, a conversion yield of 0.74 g/g, and a volumetric productivity of 0.82 g/L/h.

CONCLUSION

W. anomalus WC 1501 confirmed as an excellent producer of D-arabitol, exhibiting a remarkable capability of transforming pure glycerol. The study reports among the highest values ever reported for microbial transformation of glycerol into D-arabitol, in terms of arabitol titer, conversion yield, and productivity.

The Effect of Different Substrates on the Morphological Features and Polyols Production of Endomyces magnusii Yeast during Long-Lasting Cultivation

The study on the influence of different glucose concentrations (2%, 0.5%, and 0.2%) and glycerol (1%) on the morphological and physiological features, as well as the composition of soluble carbohydrates, was performed using Endomyces magnusii yeast. Two-factor analysis of variance with repetitions to process the data of the cell size changes showed that the substrate type affected cell size the most. The cells with 2% glucose were 30–35% larger than those growing on glycerol. The decrease in the initial glucose concentration up to 0.5–0.2% slightly changed the cell length. However, even in the logarithmic growth phase pseudo-mycelium of two to four cells appeared in the cultures when using low glucose, unlike those using glycerol. Throughout the whole experiment, more than 90% of the populations remained viable on all of the substrates tested. The ability for colony formation decreased during aging. Nevertheless, at the three-week stage, upon substrate restriction (0.2% glucose), it was twice higher than those under the other conditions. The respiration rate also decreased and exceeded not more than 10% of that in the logarithmic phase. By the end of the experiment, the cyanide-sensitive respiration share decreased up to 40% for all types of substrates. The study of soluble cytosol carbohydrates showed that the cultures using 2% glucose and 1% glycerol contained mainly arabitol and mannitol, while at low glucose concentrations they were substituted for inositol. The formation of inositol is supposed to be related to pseudo-mycelium formation. The role of calorie restriction in the regulation of carbohydrate synthesis and the composition in the yeast and its biotechnological application is under consideration.

Saccharides in atmospheric particulate and sedimentary organic matter: Status overview and future perspectives

Saccharides are omnipresent compounds in terrestrial and marine ecosystems. Since the 2000s, their role in environmental and geochemical studies has significantly increased, but only anhydrosaccharides (mainly levoglucosan) have been reviewed. Here we present the wider knowledge about saccharides in organic matter of aerosols, bottom sediments, soils, dust, and sedimentary rocks. The main purpose here is to characterize the possible sources of saccharides, as well as sacharol formation, seasonal variability, and the possible applications in environmental and paleoenvironmental interpretations. Different saccharide sources were designated, including biomass burning, and particulate matter such as pollen, spores, lichen, and fungi, as well as polysaccharide decomposition as possible inputs of monosaccharides. The main focus was on the most common saccharides encountered in environmental samples and sedimentary rocks. These are the mono- and disaccharides glucose, fructose, sucrose, and trehalose, and sacharols arabitol and mannitol. The anhydrosaccharides levoglucosan, mannosan, and galactosan were evaluated as ancient wildfire indicators and industrialization tracers found in lacustrine sediments starting from Pleistocene to contemporary deposits. However, other anhydrosaccharides like xylosan and arabinosan were also found as products of fossil wood burning. These anhydrosaccharides have the potential to be further tracers of hemicellulose burning. Additional recommendations are proposed for future research, including environmental and paleoenvironmental topics that need to be addressed.

Utilizing yeasts for the conversion of renewable feedstocks to sugar alcohols - a review

Sugar alcohols are widely marketed compounds. They are useful building block chemicals and of particular value as low- or non-calorigenic sweeteners, serving as sugar substitutes in the food industry. To date most sugar alcohols are produced by chemical routes using pure sugars, but a transition towards the use of renewable, non-edible feedstocks is anticipated. Several yeasts are naturally able to convert renewable feedstocks, such as lignocellulosic substrates, glycerol and molasses, into sugar alcohols. These bioconversions often face difficulties to obtain sufficiently high yields and productivities necessary for industrialization. This review provides insight into the most recent studies on utilizing yeasts for the conversion of renewable feedstocks to diverse sugar alcohols, including xylitol, erythritol, mannitol and arabitol. Moreover, metabolic approaches are highlighted that specifically target shortcomings of sugar alcohol production by yeasts from these renewable substrates.

Bioconversions of Biodiesel-Derived Glycerol into Sugar Alcohols by Newly Isolated Wild-Type Yarrowia lipolytica Strains

The utilization of crude glycerol, generated as a by-product from the biodiesel production process, for the production of high value-added products represents an opportunity to overcome the negative impact of low glycerol prices in the biodiesel industry. In this study, the biochemical behavior of Yarrowia lipolytica strains FMCC Y-74 and FMCC Y-75 was investigated using glycerol as a carbon source. Initially, the effect of pH value (3.0–7.0) was examined to produce polyols, intracellular lipids, and polysaccharides. At low pH values (initial pH 3.0–5.0), significant mannitol production was recorded. The highest mannitol production (19.64 g L−1) was obtained by Y. lipolytica FMCC Y-74 at pH = 3.0. At pH values ranging between 5.0 and 6.0, intracellular polysaccharides synthesis was favored, while polyols production was suppressed. Subsequently, the effect of crude glycerol and its concentration on polyols production was studied. Y. lipolytica FMCC Y-74 showed high tolerance to impurities of crude glycerol. Initial substrate concentrations influence polyols production and distribution with a metabolic shift toward erythritol production being observed when the initial glycerol concentration (Gly0) increased. The highest total polyols production (=56.64 g L−1) was obtained at Gly0 adjusted to ≈120 g L−1. The highest polyols conversion yield (0.59 g g−1) and productivity (4.36 g L−1 d−1) were reached at Gly0 = 80 g L−1. In fed-batch intermittent fermentation with glycerol concentration remaining ≤60 g L−1, the metabolism was shifted toward mannitol biosynthesis, which was the main polyol produced in significant quantities (=36.84 g L−1) with a corresponding conversion yield of 0.51 g g−1.

Beetroot juice - a suitable post-marathon metabolic recovery supplement?

BACKGROUND

Red beetroot (Beta vulgaris L.) is a multifunctional functional food that reportedly exhibits potent anti-inflammatory, antioxidant, vasodilation, and cellular regulatory properties. This vegetable has gained a fair amount of scientific attention as a possible cost-effective supplement to enhance performance and expedite recovery after physical exercise. To date, no study has investigated the effects of incremental beetroot juice ingestion on the metabolic recovery of athletes after an endurance race. Considering this, as well as the beneficial glucose and insulin regulatory roles of beetroot, this study investigated the effects of beetroot juice supplementation on the metabolic recovery trend of athletes within 48 h after completing a marathon.

METHODS

By employing an untargeted two-dimensional gas chromatography time-of-flight mass spectrometry approach, serum samples (collected pre-, post-, 24 h post-, and 48 h post-marathon) of 31 marathon athletes that ingested a series (n = 7; 250 ml) of either beetroot juice (n = 15 athletes) or isocaloric placebo (n = 16 athletes) supplements within 48 h post-marathon, were analysed and statistically compared.

RESULTS

The metabolic profiles of the beetroot-ingesting cohort recovered to a pre-marathon-related state within 48 h post-marathon, mimicking the metabolic recovery trend observed in the placebo cohort. Since random inter-individual variation was observed immediately post-marathon, only metabolites with large practical significance (p-value ≤0.05 and d-value ≥0.5) within 24 h and 48 h post-marathon were considered representative of the effects of beetroot juice on metabolic recovery. These (n = 4) mainly included carbohydrates (arabitol and xylose) and odd-chain fatty acids (nonanoate and undecanoate). The majority of these were attributed to beetroot content and possible microbial fermentation thereof.

CONCLUSION

Apart from the global metabolic recovery trends of the two opposing cohorts, it appears that beetroot ingestion did not expedite metabolic recovery in athletes within 48 h post-marathon.

High D-arabitol production with osmotic pressure control fed-batch fermentation by Yarrowia lipolytica and proteomic analysis under nitrogen source perturbation

D-arabitol, a five-carbon sugar alcohol, is widely used in food and pharmacy industry as a lower calorie sweetener or intermediate. Appropriate osmotic pressure was confirmed to facilitate polyol production by an osmophilic yeast strain of Yarrowia lipolytica with glycerol. In this study, an osmotic pressure control fed-batch fermentation strategy was used for high D-arabitol producing by Y. lipolytica ARA9 with crude glycerol. Glycerol was added to the broth quantitatively not only as a substrate but also as an osmotic agent. Meanwhile, NH₃·H₂O was fed as a nitrogen source and pH regulator. The maximum D-arabitol production reached 118.5 g/L at 108 h with the yield of 0.49 g/g and productivity of 1.10 g/L/h, respectively. Furthermore, a comparative proteomic analysis was used to study the cellular responses under excess and deficient nitrogen sources. Thirty-one differentially expressed protein spots belonging to seven different biological processes were identified. Excess nitrogen source enhanced gluconeogenesis and pentose phosphate pathways, both of which were involved in arabitol synthesis. In addition, cell growth was facilitated by increased expression of nucleotide and structural proteins. Enhanced energy and NADPH biosynthesis were employed to create a reductive environment and quell reactive oxygen species, improving D-arabitol production. Nitrogen deficiency resulted in cell rescue and stress response mechanisms such as reactive oxygen species elimination and heat shock protein response. The identified differentially expressed proteins provide information to reveal the mechanisms of the cellular responses under nitrogen source perturbation, and also provide guidance to improve D-arabitol production in metabolic engineering or process optimization methodologies.

Antifungal activity of polymethyl methacrylate/Si3N4 composites against Candida albicans

Previous studies using gram-positive and -negative bacteria demonstrated that hydrolysis of silicon nitride (Si₃N₄) in aqueous suspensions elutes nitrogen and produces gaseous ammonia while buffering pH. According to immunochemistry assays, fluorescence imaging, and in situ Raman spectroscopy, we demonstrate here that the antipathogenic surface chemistry of Si₃N₄ can be extended to polymethylmethacrylate (PMMA) by compounding it with a minor fraction (~8 vol.%) of Si₃N₄ particles without any tangible loss in bulk properties. The hydrolytic products, which were eluted from partly exposed Si₃N₄ particles at the composite surface, exhibited fungicidal action against Candida albicans. Using a specific nitrative stress sensing dye and highly resolved fluorescence micrographs, we observed in situ congestion of peroxynitrite (ONOO^-) radicals in the mitochondria of the Candida cells exposed to the PMMA/Si₃N₄ composite, while these radicals were absent in the mitochondria of identical cells exposed to monolithic PMMA. These in situ observations suggest that the surface chemistry of Si₃N₄ mimics the antifungal activity of macrophages, which concurrently produce NO radicals and superoxide anions (O₂•^-) resulting in the formation of candidacidal ONOO^-. The fungicidal properties of PMMA/Si₃N₄ composites could be used in dental appliances to inhibit the uncontrolled growth of Candida albicans and ensuing candidiasis while being synergic with chemoprophylaxis. STATEMENT OF SIGNIFICANCE: In a follow-up of previous studies of gram-positive and gram-negative bacteria, we demonstrate here that the antipathogenic surface chemistry of Si₃N₄ could be extended to polymethylmethacrylate (PMMA) containing a minor fraction (~8 vol.%) of Si₃N₄ particles without tangible loss in bulk properties. Hydrolytic products eluted from Si₃N₄ particles at the composite surface exhibited fungicidal action against Candida albicans. Highly resolved fluorescence microscopy revealed congestion of peroxynitrite (ONOO^-) radicals in the mitochondria of the Candida cells exposed to the PMMA/Si₃N₄ composite, while radicals were absent in the mitochondria of identical cells exposed to monolithic PMMA. The fungicidal properties of PMMA/Si₃N₄ composites could be used in dental appliances to inhibit uncontrolled growth of Candida albicans and ensuing candidiasis in synergy with chemoprophylaxis.

GC-MS-Based Metabolomics Study of Single- and Dual-Species Biofilms of Candida albicans and Klebsiella pneumoniae

Candida albicans and Klebsiella pneumoniae frequently co-exist within the human host as a complex biofilm community. These pathogens are of interest because their association is also related to significantly increased morbidity and mortality in hospitalized patients. With the aim of highlighting metabolic shifts occurring in the dual-species biofilm, an untargeted GC-MS-based metabolomics approach was applied to single and mixed biofilms of C. albicans and K. pneumoniae. Metabolomic results showed that among the extracellular metabolites identified, approximately 40 compounds had significantly changed relative abundance, mainly involving central carbon, amino acid, vitamin, and secondary metabolisms, such as serine, leucine, arabitol, phosphate, vitamin B6, cyclo-(Phe-Pro), trehalose, and nicotinic acid. The results were related to the strict interactions between the two species and the different microbial composition in the early and mature biofilms.

Engineering xylose metabolism in yeasts to produce biofuels and chemicals

Xylose is the second most abundant sugar in lignocellulosic biomass. Efficient and rapid xylose utilization is essential for the economic bioconversion of lignocellulosic biomass into value-added products. Building on previous pathway engineering efforts to enable xylose fermentation in Saccharomyces cerevisiae, recent work has focused on reprogramming regulatory networks to enhance xylose utilization by engineered S. cerevisiae. Also, potential benefits of using xylose for the production of various value-added products have been demonstrated. With increasing needs of lipid-derived bioproducts, activation and enhancement of xylose metabolism in oleaginous yeasts have been attempted. This review highlights recent progress of metabolic engineering to achieve efficient and rapid xylose utilization by S. cerevisiae and oleaginous yeasts, such as Yarrowia lipolytica, Rhodosporidium toruloides, and Lipomyces starkeyi.

The Urine Metabolome of Young Autistic Children Correlates with Their Clinical Profile Severity

Autism diagnosis is moving from the identification of common inherited genetic variants to a systems biology approach. The aims of the study were to explore metabolic perturbations in autism, to investigate whether the severity of autism core symptoms may be associated with specific metabolic signatures; and to examine whether the urine metabolome discriminates severe from mild-to-moderate restricted, repetitive, and stereotyped behaviors. We enrolled 57 children aged 2–11 years; thirty-one with idiopathic autism and twenty-six neurotypical (NT), matched for age and ethnicity. The urine metabolome was investigated by gas chromatography-mass spectrometry (GC-MS). The urinary metabolome of autistic children was largely distinguishable from that of NT children; food selectivity induced further significant metabolic differences. Severe autism spectrum disorder core deficits were marked by high levels of metabolites resulting from diet, gut dysbiosis, oxidative stress, tryptophan metabolism, mitochondrial dysfunction. The hierarchical clustering algorithm generated two metabolic clusters in autistic children: 85–90% of children with mild-to-moderate abnormal behaviors fell in cluster II. Our results open up new perspectives for the more general understanding of the correlation between the clinical phenotype of autistic children and their urine metabolome. Adipic acid, palmitic acid, and 3-(3-hydroxyphenyl)-3-hydroxypropanoic acid can be proposed as candidate biomarkers of autism severity.

Exploiting new biorefinery models using non-conventional yeasts and their implications for sustainability

Feasible bioprocessing of lignocellulosic biomass requires the use of microbial strains with tolerance to inhibitor compounds and osmotic pressure, able to provide high product yield and productivity. In this sense, this study evaluated the potential of two non-conventional yeasts, Hansenula polymorpha CBS 4732 and Debaryomyces hansenii CBS 767, for use on biomass conversion in a biorefinery perspective. The ability of the strains to consume pentose and hexose sugars, to resist the toxic compounds present in hydrolysates, as well as to produce sugar alcohols and ethanol, was investigated. H. polymorpha showed highlighted resistance to toxic compounds and relevant ability to consume xylose and produce xylitol and ethanol under these conditions, at 37 °C. D. hansenii was a great producer of arabitol from glucose. The implications for sustainability due to the use of these yeasts in biorefineries was discussed. These results open up new perspectives for the development of the biorefinery sector.

The Improvement of Bioethanol Production by Pentose-Fermenting Yeasts Isolated from Herbal Preparations, the Gut of Dung Beetles, and Marula Wine

Efficient conversion of pentose sugars to ethanol is important for an economically viable lignocellulosic bioethanol process. Ten yeasts fermenting both D-xylose and L-arabinose were subjected to an adaptation process with L-arabinose as carbon source in a medium containing acetic acid. Four Meyerozyma caribbica-adapted strains were able to ferment L-arabinose to ethanol in the presence of 3 g/L acetic acid at 35°C. Meyerozyma caribbica Mu 2.2f fermented L-arabinose to produce 3.0 g/L ethanol compared to the parental strain with 1.0 g/L ethanol in the absence of acetic acid. The adapted M. caribbica Mu 2.2f strain produced 3.6 and 0.8 g/L ethanol on L-arabinose and D-xylose, respectively, in the presence of acetic acid while the parental strain failed to grow. In a bioreactor, the adapted M. caribbica Mu 2.2f strain produced 5.7 g/L ethanol in the presence of 3 g/L acetic acid with an ethanol yield and productivity of 0.338 g/g and 0.158 g/L/h, respectively, at a K _L a value of 3.3 h^-1. The adapted strain produced 26.7 g/L L-arabitol with a yield of 0.900 g/g at a K _L a value of 4.9 h^-1.

Combined mutagenesis and metabolic regulation to enhance D-arabitol production from Candida parapsilosis

D-Arabitol is an important pentitol that is widely used in the food, pharmaceutical and chemical industries. It is mainly produced by yeasts during the biotransformation of glucose. To obtain strains with high D-arabitol production, Candida parapsilosis was mutated using atmospheric and room temperature plasma (ARTP). Among the screened mutants, mutant A6 had the highest yield at 32.92 g/L, a 53.98% increase compared with the original strain (21.38 g/L). Furthermore, metabolic regulators were added to the medium to improve D-arabitol production. Pyrithioxin dihydrochloride increased D-arabitol production by 34.4% by regulating glucose-6-phosphate dehydrogenase, and 4-methylpyrazole increased D-arabitol production by 77.4% compared with the control group by inhibiting alcohol dehydrogenase activity. Amphotericin B and Triton X-100 increased D-arabitol production by 23.8% and 42.2% by improving the membrane permeability and dissolved oxygen content, respectively. This study may provide important implications for obtaining high-yield D-arabitol strains.

Sugar Alcohols and Organic Acids Synthesis in Yarrowia lipolytica: Where Are We?

Sugar alcohols and organic acids that derive from the metabolism of certain microorganisms have a panoply of applications in agro-food, chemical and pharmaceutical industries. The main challenge in their production is to reach a productivity threshold that allow the process to be profitable. This relies on the construction of efficient cell factories by metabolic engineering and on the development of low-cost production processes by using industrial wastes or cheap and widely available raw materials as feedstock. The non-conventional yeast Yarrowia lipolytica has emerged recently as a potential producer of such metabolites owing its low nutritive requirements, its ability to grow at high cell densities in a bioreactor and ease of genome edition. This review will focus on current knowledge on the synthesis of the most important sugar alcohols and organic acids in Y. lipolytica.

Occurrence and Molecular Identification of Wild Yeasts from Jimma Zone, South West Ethiopia

Yeasts are common inhabitants of most fruit trees' rhizospheres and phyllospheres. Wild yeasts are the major driving force behind several modern industrial biotechnologies. This study focused on determining the occurrence and frequency of wild yeasts associated with domestic and wild edible tree barks, fruits, and rhizosphere soil samples collected over two seasons (i.e., spring and summer) in South West Ethiopia. A total of 182 yeast strains were isolated from 120 samples. These strains belonged to 16 genera and 27 species as identified based on the sequence analysis of the D1/D2 domain of the large subunit (26S) ribosomal RNA gene. Candida blattae, Pichia kudriavzevii, Candida glabrata, Saccharomyces cerevisiae, and Candida humilis were the most dominant yeast species isolated from the bark samples. Only Pichia kudriavzevii was regularly detected from the bark, rhizosphere, fruit, and sugarcane samples. The retrieval of yeasts from bark samples was more frequent and diverse than that of soil, fruits, and sugarcane. The frequency of detection of yeasts during the spring was significantly higher than in the summer season. However, there was no significant seasonal variation in the frequency of detection of yeast species between the rhizosphere and phyllosphere samples.

Characterization of D-Arabitol as Newly Discovered Carbon Source of Bacillus methanolicus

Bacillus methanolicus is a Gram-positive, thermophilic, methanol-utilizing bacterium. As a facultative methylotroph, B. methanolicus is also known to utilize D-mannitol, D-glucose and, as recently discovered, sugar alcohol D-arabitol. While metabolic pathways for utilization of methanol, mannitol and glucose are known, catabolism of arabitol has not yet been characterized in B. methanolicus. In this work we present the elucidation of this hitherto uncharted pathway. In order to confirm our predictions regarding genes coding for arabitol utilization, we performed differential gene expression analysis of B. methanolicus MGA3 cells grown on arabitol as compared to mannitol via transcriptome sequencing (RNA-seq). We identified a gene cluster comprising eight genes that was up-regulated during growth with arabitol as a sole carbon source. The RNA-seq results were subsequently confirmed via qRT-PCR experiments. The transcriptional organization of the gene cluster identified via RNA-seq was analyzed and it was shown that the arabitol utilization genes are co-transcribed in an operon that spans from BMMGA3_RS07325 to BMMGA3_RS07365. Since gene deletion studies are currently not possible in B. methanolicus, two complementation experiments were performed in an arabitol negative Corynebacterium glutamicum strain using the four genes discovered via RNA-seq analysis as coding for a putative PTS for arabitol uptake (BMMGA3_RS07330, BMMGA3_RS07335, and BMMGA3_RS07340 renamed to atlABC) and a putative arabitol phosphate dehydrogenase (BMMGA3_RS07345 renamed to atlD). C. glutamicum is a natural D-arabitol utilizer that requires arabitol dehydrogenase MtlD for arabitol catabolism. The C. glutamicum mtlD deletion mutant was chosen for complementation experiments. Heterologous expression of atlABCD as well as the arabitol phosphate dehydrogenase gene atlD from B. methanolicus alone restored growth of the C. glutamicum ΔmtlD mutant with arabitol. Furthermore, D-arabitol phosphate dehydrogenase activities could be detected in crude extracts of B. methanolicus and these were higher in arabitol-grown cells than in methanol- or mannitol-grown cells. Thus, B. methanolicus possesses an arabitol inducible operon encoding, amongst others, a putative PTS system and an arabitol phosphate dehydrogenase for uptake and activation of arabitol as growth substrate.

Torulaspora delbrueckii produces high levels of C5 and C6 polyols during wine fermentations

Non-Saccharomyces yeasts impact wine fermentations and can diversify the flavor profiles of wines. However, little information is available on the metabolic networks of most of these species. Here we show that unlike the main wine yeast Saccharomyces cerevisiae, Torulaspora delbrueckii and to a lesser extent Lachancea thermotolerans produce significant concentrations of C5 and C6 polyols under wine fermentation conditions. In particular, D-arabitol, D-sorbitol and D-mannitol were produced at significant levels. Their release into the extracellular matrix started when that of glycerol ceased. The data also show that polyol production is influenced by initial sugar concentration, repressed by acetic acid and induced in ethanol supplemented media. Moreover, unlike glycerol and sorbitol, mannitol was partially re-assimilated when populations started to decline. The findings suggest that polyol synthesis is a physiological adaptation to stressful conditions characteristic of alcoholic fermentation and that these polyols may serve a similar purpose as glycerol production in S. cerevisiae, including osmoadaptation and redox balancing.

Production of galactitol from galactose by the oleaginous yeast Rhodosporidium toruloides IFO0880

BACKGROUND

Sugar alcohols are commonly used as low-calorie sweeteners and can serve as potential building blocks for bio-based chemicals. Previous work has shown that the oleaginous yeast Rhodosporidium toruloides IFO0880 can natively produce arabitol from xylose at relatively high titers, suggesting that it may be a useful host for sugar alcohol production. In this work, we explored whether R. toruloides can produce additional sugar alcohols.

RESULTS

Rhodosporidium toruloides is able to produce galactitol from galactose. During growth in nitrogen-rich medium, R. toruloides produced 3.2 ± 0.6 g/L, and 8.4 ± 0.8 g/L galactitol from 20 to 40 g/L galactose, respectively. In addition, R. toruloides was able to produce galactitol from galactose at reduced titers during growth in nitrogen-poor medium, which also induces lipid production. These results suggest that R. toruloides can potentially be used for the co-production of lipids and galactitol from galactose. We further characterized the mechanism for galactitol production, including identifying and biochemically characterizing the critical aldose reductase. Intracellular metabolite analysis was also performed to further understand galactose metabolism.

CONCLUSIONS

Rhodosporidium toruloides has traditionally been used for the production of lipids and lipid-based chemicals. Our work demonstrates that R. toruloides can also produce galactitol, which can be used to produce polymers with applications in medicine and as a precursor for anti-cancer drugs. Collectively, our results further establish that R. toruloides can produce multiple value-added chemicals from a wide range of sugars.

Continuous enzymatic hydrolysis of sugar beet pectin and l-arabinose recovery within an integrated biorefinery

Sugar beet pulp (SBP) fractionated by steam explosion, released sugar beet pectin (SB-pectin) which was selectively hydrolysed using a novel α-l-arabinofuranosidase (AF), yielding monomeric l-arabinose (Ara) and a galacturonic acid rich backbone (GABB). AF was immobilised on an epoxy-functionalised resin with 70% overall immobilisation yield. Pretreatment of SB-pectin, to remove coloured compounds, improved the stability of the immobilised AF, allowing its reutilisation for up to 10 reaction cycles in a stirred tank reactor. Continuous hydrolysis of SB-pectin was subsequently performed using a packed bed reactor (PBR) with immobilised AF. Reactor performance was evaluated using a Design of Experiment approach. Pretreated SB-pectin hydrolysis was run for 7 consecutive days maintaining 73% of PBR performance. Continuous separation of Ara from GABB was achieved by tangential flow ultrafiltration with 92% Ara recovery. These results demonstrate the feasibility of establishing a continuous bioprocess to obtain Ara from the inexpensive SBP biomass.