Metabolic correlation between polyol and energy-storing carbohydrate under osmotic and oxidative stress condition in Moniliella megachiliensis

Research progress on biosynthesis of erythritol and multi-dimensional optimization of production strategies

Erythritol, as a new type of natural sweetener, has been widely used in food, medical, cosmetics, pharmaceutical and other fields due to its unique physical and chemical properties and physiological functions. In recent years, with the continuous development of strategies such as synthetic biology, metabolic engineering, omics-based systems biology and high-throughput screening technology, people's understanding of the erythritol biosynthesis pathway has gradually deepened, and microbial cell factories with independent modification capabilities have been successfully constructed. In this review, the cheap feedstocks for erythritol synthesis are introduced in detail, the environmental factors affecting the synthesis of erythritol and its regulatory mechanism are described, and the tools and strategies of metabolic engineering involved in erythritol synthesis are summarized. In addition, the study of erythritol derivatives is helpful in expanding its application field. Finally, the challenges that hinder the effective production of erythritol are discussed, which lay a foundation for the green, efficient and sustainable production of erythritol in the future and breaking through the bottleneck of production.

Transcriptome analysis reveals multiple targets of erythritol-related transcription factor EUF1 in unconventional yeast Yarrowia Lipolytica

BACKGROUND

Erythritol is a four-carbon polyol with an unclear role in metabolism of some unconventional yeasts. Its production has been linked to the osmotic stress response, but the mechanism of stress protection remains unclear. Additionally, erythritol can be used as a carbon source. In the yeast Yarrowia lipolytica, its assimilation is activated by the transcription factor Euf1. The study investigates whether this factor can link erythritol to other processes in the cell.

RESULTS

The research was performed on two closely related strains of Y. lipolytica: MK1 and K1, where strain K1 has no functional Euf1. Cultures were carried out in erythritol-containing and erythritol-free media. Transcriptome analysis revealed the effect of Euf1 on the regulation of more than 150 genes. Some of these could be easily connected with different aspects of erythritol assimilation, such as: utilization pathway, a new potential isoform of transketolase, or polyol transporters. However, many of the upregulated genes have never been linked to metabolism of erythritol. The most prominent examples are the degradation pathway of branched-chain amino acids and the glyoxylate cycle. The high transcription of genes affected by Euf1 is still dependent on the erythritol concentration in the medium. Moreover, almost all up-regulated genes have an ATGCA motif in the promoter sequence.

CONCLUSIONS

These findings may be particularly relevant given the increasing use of erythritol-induced promoters in genetic engineering of Y. lipolytica. Moreover, use of this yeast in biotechnological processes often takes place under osmotic stress conditions. Erythritol might be produce as a by-product, thus better understanding of its influence on cell metabolism could facilitate processes optimization.

Symbiotic bacteria and fungi proliferate in diapause and may enhance overwintering survival in a solitary bee

Host-microbe interactions underlie the development and fitness of many macroorganisms, including bees. Whereas many social bees benefit from vertically transmitted gut bacteria, current data suggests that solitary bees, which comprise the vast majority of species diversity within bees, lack a highly specialized gut microbiome. Here, we examine the composition and abundance of bacteria and fungi throughout the complete life cycle of the ground-nesting solitary bee Anthophora bomboides standfordiana. In contrast to expectations, immature bee stages maintain a distinct core microbiome consisting of Actinobacterial genera (Streptomyces, Nocardiodes) and the fungus Moniliella spathulata. Dormant (diapausing) larval bees hosted the most abundant and distinctive bacteria and fungi, attaining 33 and 52 times their initial copy number, respectively. We tested two adaptive hypotheses regarding microbial functions for diapausing bees. First, using isolated bacteria and fungi, we found that Streptomyces from brood cells inhibited the growth of multiple pathogenic filamentous fungi, suggesting a role in pathogen protection during overwintering, when bees face high pathogen pressure. Second, sugar alcohol composition changed in tandem with major changes in fungal abundance, suggesting links with bee cold tolerance or overwintering biology. We find that A. bomboides hosts a conserved core microbiome that may provide key fitness advantages through larval development and diapause, which raises the question of how this microbiome is maintained and faithfully transmitted between generations. Our results suggest that focus on microbiomes of mature or active insect developmental stages may overlook stage-specific symbionts and microbial fitness contributions during host dormancy.

Construction of a xylose metabolic pathway in Trichosporonoides oedocephalis ATCC 16958 for the production of erythritol and xylitol

PURPOSE

Erythritol is a valuable compound as sweetener and chemical material however cannot be fermented from the abundant substrate xylose.

METHODS

The strain Trichosporonoides oedocephalis ATCC 16958 was employed to produce polyols including xylitol and erythritol by metabolic engineering approaches.

RESULTS

The introduction of a substrate-specific ribose-5-phosphate isomerase endowed T. oedocephalis with xylose-assimilation activity to produce xylitol, and eliminated glycerol production simultaneously. A more value-added product, erythritol was produced by further introducing a homologous xylulose kinase. The carbon flux was redirected from xylitol to erythritol by adding high osmotic pressure. The production of erythritol was improved to 46.5 g/L in flasks by fermentation adjustment, and the process was scaled up in a 5-L fermentor, with a 40 g/L erythritol production after 120 h, and a time-space yield of 0.56 g/L/h.

CONCLUSION

This study demonstrated the potential of T. oedocephalis in the synthesis of multiple useful products from xylose.

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.

Hyperosmolarity adversely impacts recombinant protein synthesis by Yarrowia lipolytica-molecular background revealed by quantitative proteomics

Abstract

In this research, we were interested in answering a question whether subjecting a Yarrowia lipolytica strain overproducing a recombinant secretory protein (rs-Prot) to pre-optimized stress factors may enhance synthesis of the rs-Prot. Increased osmolarity (3 Osm kg⁻¹) was the primary stress factor implemented alone or in combination with decreased temperature (20 °C), known to promote synthesis of rs-Prots. The treatments were executed in batch bioreactor cultures, and the cellular response was studied in terms of culture progression, gene expression and global proteomics, to get insight into molecular bases underlying an awaken reaction. Primarily, we observed that hyperosmolarity executed by high sorbitol concentration does not enhance synthesis of the rs-Prot but increases its transcription. Expectedly, hyperosmolarity induced synthesis of polyols at the expense of citric acid synthesis and growth, which was severely limited. A number of stress-related proteins were upregulated, including heat-shock proteins (HSPs) and aldo–keto reductases, as observed at transcriptomics and proteomics levels. Concerted downregulation of central carbon metabolism, including glycolysis, tricarboxylic acid cycle and fatty acid synthesis, highlighted redirection of carbon fluxes. Elevated abundance of HSPs and osmolytes did not outbalance the severe limitation of protein synthesis, marked by orchestrated downregulation of translation (elongation factors, several aa-tRNA synthetases), amino acid biosynthesis and ribosome biogenesis in response to the hyperosmolarity. Altogether we settled that increased osmolarity is not beneficial for rs-Prots synthesis in Y. lipolytica, even though some elements of the response could assist this process. Insight into global changes in the yeast proteome under the treatments is provided.

Key points

• Temp enhances, but Osm decreases rs-Prots synthesis by Y. lipolytica.

• Enhanced abundance of HSPs and osmolytes is overweighted by limited translation.

• Global proteome under Osm, Temp and Osm Temp treatments was studied.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11731-y.

Thermal treatment improves a process of crude glycerol valorization for the production of a heterologous enzyme by Yarrowia lipolytica

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A crude glycerol valorization process to enzymatic preparation was developed.

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Impact of thermal treatment on the protein production by Y. lipolytica is studied.

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Pilot-scale processes with laboratory and technical substrates were simulated.

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Techno-economic analysis of a pilot-scale waste-free process was conducted.

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Comprehensive stream analysis and identification of bottlenecks is provided.

Valorization of crude glycerol requires a potent bifunctional biocatalyst, such as Yarrowia lipolytica, capable of high-density growth on this substrate, and having i.a. high propensity for heterologous protein synthesis. Increasing evidence suggests that controlled administration of stress, i.a. thermal treatment, has a positive impact on bioprocess performance. In this study, we systematically adjusted thermal treatment conditions (20 to 42 °C) in order to maximize heterologous protein production by Y. lipolytica growing in crude glycerol-based medium. Our results showed nearly 30% enhancement in the enzyme production triggered by temporary exposure to decreased temperature. Here developed mathematical model indicated optimal treatment conditions (20 °C, 153′) that were later applied to a process with biodiesel-derived glycerol and technical substrates. Techno-economic analysis of a pilot-scale-waste-free process was conducted. Quantitative description of the associated costs and economic gain due to exploitation of industrial substrates, as well as indication of current bottlenecks of the process, are also provided.

HOG-Independent Osmoprotection by Erythritol in Yeast Yarrowia lipolytica

Erythritol is a polyol produced by Yarrowia lipolytica under hyperosmotic stress. In this study, the osmo-sensitive strain Y. lipolytica yl-hog1Δ was subjected to stress, triggered by a high concentration of carbon sources. The strain thrived on 0.75 M erythritol medium, while the same concentrations of glucose and glycerol proved to be lethal. The addition of 0.1 M erythritol to the medium containing 0.75 M glucose or glycerol allowed the growth of yl-hog1Δ. Supplementation with other potential osmolytes such as mannitol or L-proline did not have a similar effect. To examine whether the osmoprotective effect might be related to erythritol accumulation, we deleted two genes involved in erythritol utilization, the transcription factor Euf1 and the enzyme erythritol dehydrogenase Eyd1. The strain eyd1Δ yl hog1Δ, which lacked the erythritol utilization enzyme, reacted to the erythritol supplementation significantly better than yl-hog1Δ. On the other hand, the strain euf1Δ yl-hog1Δ became insensitive to supplementation, and the addition of erythritol could no longer improve the growth of this strain in hyperosmotic conditions. This indicates that Euf1 regulates additional, still unknown genes involved in erythritol metabolism.

Erythritol: Another C4 Platform Chemical in Biomass Refinery

The potential of erythritol as a platform chemical in biomass refinery is discussed in terms of erythritol production and utilization. Regarding erythritol production, fermentation of sugar or starch has been already commercialized. The shift of the carbon source from glucose to inexpensive inedible waste glycerol is being investigated, which will decrease the price of erythritol. The carbon-based yield of erythritol from glycerol is comparable to or even higher than that from glucose. The metabolic pathway of erythritol biosynthesis has become clarified: erythrose-4-phosphate, which is one of the intermediates in the pentose phosphate pathway, is dephosphorylated and reduced to erythritol. The information about the metabolic pathway may give insights to improve the productivity by bleeding. Regarding erythritol utilization, chemical conversions of erythritol, especially deoxygenation, have been investigated in these days. Erythritol is easily dehydrated to 1,4-anhydroerythritol, which can be also used as the substrate for production of useful C4 chemicals. C-O hydrogenolysis and deoxydehydration using heterogeneous catalysts are effective reactions for erythritol/1,4-anhydroerythritol conversion.

Soluble Sugar and Lipid Readjustments in the Yarrowia lipolytica Yeast at Various Temperatures and pH

Microorganisms cope with a wide range of environmental challenges using different mechanisms. Their ability to prosper at extreme ambient pH and high temperatures has been well reported, but the adaptation mechanism often remains unrevealed. In this study, we addressed the dynamics of lipid and sugar profiles upon different cultivation conditions. The results showed that the cells grown at various pH and optimal temperature contained mannitol as the major cytosol sugar alcohol. The elevated temperature of 38 °C led to a two- to three-fold increase in total cytosol sugars with concurrent substitution of mannitol for trehalose. Lipid composition in the cells at optimal temperature changed insignificantly at any pH tested. The increase in the temperature caused some drop in the storage and membrane lipid levels, remarkable changes in their composition, and the degree of unsaturated fatty acids. It was shown that the fatty acid composition of some membrane phospholipids varied considerably at changing pH and temperature values. The data showed a pivotal role and flexibility of the sugar and lipid composition of Y. lipolytica W29 in adaptation to unfavorable environmental conditions.

Metabolites analysis for cold-resistant yeast (Wickerhamomyces anomalus) strains own antioxidant activity on cold stored fish mince

The effect of eight cold-resistant yeast strains (J3, J7, J8, J9, J12, J15, J18, and J25) of Wickerhamomyces anomalus on the lipid oxidation of cold stored fish mince (4 °C) were investigated. And the metabolites of these yeast were determined with gas chromatography-mass spectrometry. These strains could effectively inhibit the increase of hydroperoxides value (p < 0.05), and the inhibiting rate was positively correlated with the content of isolongifolene, xylitol, turanose, thymol-glucoside, and uridine. Especially, the J3, J7, J8, J9, J12, and J18 could eliminate a large part of thiobarbituric acid reactive substances (TBARS) (p < 0.05), the eliminating rate was proportionate to the aldehyde dehydrogenase activity. Several bacteriostatic metabolites were detected: thymol-glucoside, 2-phenylethanol, cedro, and 2,4-bis (1,1-dimethylethyl) phenol. In addition, W. anomalus produced many metabolites with fruit and floral notes. In conclusion, cold-resistant W. anomalus strains own antioxidant activity were potential new bio-preservatives in the cold storage of muscle products.

Combined Transcriptome and Proteome Analysis of RpoS Regulon Reveals Its Role in Spoilage Potential of Pseudomonas fluorescens

Microbial contamination is considered the main cause of food spoilage. Pseudomonas fluorescens is a typical spoilage bacterium contributing to a large extent to the spoilage process of proteinaceous foods. RpoS is known as an alternative sigma factor controlling stress resistance and virulence in many pathogens. Our previous work revealed that RpoS contributes to the spoilage activities of P. fluorescens by regulating resistance to different stress conditions, extracellular acylated homoserine lactone (AHL) levels, extracellular protease and total volatile basic nitrogen (TVB-N) production. However, RpoS-dependent genes in P. fluorescens remained undefined. RNA-seq transcriptomics analysis combined with quantitative proteomics analysis based on multiplexed isobaric tandem mass tag (TMT) labeling was performed in the P. fluorescens wild-type strain UK4 and its derivative carrying an rpoS mutation. A total of 375 differentially expressed coding sequences (DECs) and 212 differentially expressed proteins (DEPs) were identified. The DECs were further verified by qRT-PCR. The combined transcriptome and proteome analyses revealed the involvement of this regulator in several cellular processes, mainly including polysaccharide metabolism, intracellular secretion, extracellular structures, cell wall biogenesis, stress responses, and amino acid and biogenic amine metabolism, which may contribute to the biofilm formation, stress resistance, and spoilage activities of P. fluorescens. Moreover, we indeed observed that RpoS contributed to the production of the macrocolony biofilm's matrix. Our results provide insights into the regulatory network of RpoS and expand the knowledge about the role of RpoS in the functioning of P. fluorescens in food spoilage.

Sorbitol production and optimization of photosynthetic supply in the cyanobacterium Synechocystis PCC 6803

Biochemicals production is a major theme in the application of photosynthesis to address global warming and organic-resource problems. Among biochemicals, sugar alcohols have attracted research attention because they are directly derived from two photosynthetic products, sugars and reductants. Here, we produced sorbitol photosynthetically by using cyanobacteria and modified the supply of its substrates through genetic engineering. Expression of an NADPH-dependent enzyme that generates sorbitol-6-phosphate, S6PDH, was highly toxic to cyanobacteria likely due to the sorbitol production, whereas expression of an NADH-dependent enzyme, SrlD2, yielded no sorbitol. The toxicity was partly overcome by introducing a theophylline-inducible riboswitch for S6PDH expression and optimizing induction, but sorbitol production was still low and severely inhibited growth. Co-expression of fructose-1,6-bisphosphatase drastically alleviated the growth inhibition, but did not increase short-term sorbitol production. The NADPH/NADP⁺ ratio decreased during sorbitol production. Overexpression of a membrane-bound transhydrogenase for NADPH generation from NADH elevated the short-term sorbitol production, but only partly alleviated the growth inhibition. Notably, a strain overexpressing all three enzymes exhibited sustainable sorbitol production at 312 mg/L, which was nearly 27-fold higher than the yield of the initial S6PDH-overexpressing strain. We discuss these results in relation to the optimization of photosynthetic supply for sorbitol production in cyanobacteria.

Enhancement of erythritol production by Trichosporonoides oedocephalis ATCC 16958 through regulating key enzyme activity and the NADPH/NADP ratio with metal ion supplementation

Erythritol, a well-known natural sweetener, is mainly produced by microbial fermentation. Various metal ions (Al³⁺, Cu²⁺, Mn²⁺, and Ni²⁺) were added to the culture medium of Trichosporonoides oedocephalis ATCC 16958 at 30 mg/L in shake flask cultures. Compared with controls, Cu²⁺ increased the erythritol content by 86% and decreased the glycerol by-product by 31%. After 48 hr of shake flask culture, sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that expression levels of erythrose reductase (ER) in the presence of 30 mg/L CuSO₄ · 5H₂O were higher than those obtained after treatment with other examined metal ions. Furthermore, after 108 hr of batch culture in a 5-L bioreactor, supplementation with 30 mg/L of CuSO₄ · 5H₂O increased the specific erythritol content by 27%. Further studies demonstrated that ER activity under 30 mg/L CuSO₄ · 5H₂O supplementation in a fermentor was overtly increased compared with the control after 60 hr, while glycerol-3-phosphate dehydrogenase activity was clearly reduced in most of the fermentation process. Furthermore, the NADPH/NADP ratio was slightly lower in T. oedocephalis cells treated with Cu²⁺ compared with control cells. These results provide further insights into Cu²⁺ effects on erythritol biosynthesis in T. oedocephalis and should improve the industrial production of erythritol by biological processes.

Synthesis of 2-Butanol by Selective Hydrogenolysis of 1,4-Anhydroerythritol over Molybdenum Oxide-Modified Rhodium-Supported Silica

Rh-MoOx /SiO2 (Mo/Rh=0.13) is an effective catalyst for the hydrogenolysis of 1,4-anhydroerythritol (1,4-AHERY) and provides 2-BuOH in high yield of 51 %. This is the first report of the production of 2-BuOH from 1,4-AHERY by hydrogenolysis. 1,4-AHERY was more suitable as a starting material than erythritol because the 2-BuOH yield from erythritol was low (34 %). Based on the kinetics and comparison of reactivities of the related compounds using Rh-MoOx /SiO2 and Rh/SiO2 catalysts, the modification of Rh/SiO2 with MoOx leads to the high activity and high selectivity to 2-BuOH because of the generation of reactive hydride species and the strong adsorption of 1,4-AHERY on MoOx species. The reaction proceeds by main two routes, (I) the combination of single C-O hydrogenolysis with the desorption of intermediates, a usual route in hydrogenolysis, and (II) multiple C-O hydrogenolysis without the desorption of intermediates from the active site, and the reaction mechanism for Route (II) is proposed.