Production of arabitol from enzymatic hydrolysate of soybean flour by Debaryomyces hansenii fermentation

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.

Isolation of Zygosaccharomyces siamensis kiy1 as a novel arabitol-producing yeast and its arabitol production

Arabitol is gaining attention in the food industry as an alternative sweetener owing to its low-caloric and non-cariogenic characteristics. The yeast strain kiy1 was newly isolated from unpasteurized honey for arabitol production. Based on internal transcribed spacer sequence analysis, the isolated strain was identified as Zygosaccharomyces siamensis. In this study, the effects of different substrates and sugar concentrations on arabitol production were investigated. When three types of carbon sources (glycerol, fructose, and glucose) were used, glucose was the most suitable substrate for arabitol production (68.7 g/L). Maximum arabitol production (101.4 g/L) was observed at a glucose concentration of 30%, and the highest arabitol production yield was 0.34 g/g of initial glucose. In the time-course production of sugar alcohols by strain kiy1, glucose was completely consumed for 8 days. The concentration of arabitol exceeded that of glycerol after 3 days, and the final arabitol concentration reached 83.6 g/L after 10 days. The maximum production rate was 16.7 g/L/day. The yeast produced glycerol as an intracellular sugar alcohol in the early stage of culture and switched its metabolism to arabitol production after the middle stage. Z. siamensis kiy1 possessed an NADP⁺-dependent arabitol dehydrogenase, which indicated that it probably produces arabitol via ribulose from glucose. These results suggest that the novel yeast strain, Z. siamensis kiy1, is promising for arabitol production. The proposed arabitol production approach can contribute toward its production at the industrial scale.

Advanced strategies for production of soy-processing enzyme

Enzyme production is critical and often costly for biorefinery. It is challenging to produce enzymes with not only high titers but also proper combinations of all required activities in a single fermentation. This work aimed at improving productivity and composition of the multiple enzyme activities required for hydrolysis of complex soybean carbohydrate in a single fermentation. A previously selected Aspergillus niger strain was used for its high carbohydrases and low protease production. Strategies of fed-batch substrate addition and programmed pH-decrease rates were evaluated. Cheap soybean hull (SH) was confirmed to induce production of all necessary carbohydrases. Surprisingly, fed-batch SH addition, originally thought to sustain substrate-inducer availability and reduce feedback repression by sugars, did not increase pectinase and cellulase production significantly and even lowered the α-galactosidase production, when compared with batch fermentation having the same total SH amount (all added initially). On the other hand, the pH-decrease rate could be effectively optimized for production of complex enzyme mixtures. The best fermentation was programmed to lower pH from 7 to 4 in 84 h, at a drop rate of .0357 per h. It produced the highest pectinase (19.1 ± .04 U/mL), α-galactosidase (15.7 ± .4 U/mL), and cellulase (.88 ± .06 FPU/mL). Producing these high enzyme activities in a single fermentation significantly improves the effectiveness and economics of enzymatic soy processing, which, e.g., can hydrolyze the 30%-35% carbohydrate in soybean meal to sugars, with minimal protein degradation, to generate high-value protein-rich products and a hydrolysate as fermentation feedstock.

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.

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.

High value-added products derived from crude glycerol via microbial fermentation using Yarrowia clade yeast

BACKGROUND

Contemporary biotechnology focuses on many problems related to the functioning of developed societies. Many of these problems are related to health, especially with the rapidly rising numbers of people suffering from civilization diseases, such as obesity or diabetes. One factor contributing to the development of these diseases is the high consumption of sucrose. A very promising substitute for this sugar has emerged: the polyhydroxy alcohols, characterized by low caloric value and sufficient sweetness to replace table sugar in food production.

RESULTS

In the current study, yeast belonging to the Yarrowia clade were tested for erythritol, mannitol and arabitol production using crude glycerol from the biodiesel and soap industries as carbon sources. Out of the 13 tested species, Yarrowia divulgata and Candida oslonensis turned out to be particularly efficient polyol producers. Both species produced large amounts of these compounds from both soap-derived glycerol (59.8-62.7 g dm-3) and biodiesel-derived glycerol (76.8-79.5 g dm-3). However, it is equally important that the protein and lipid content of the biomass (around 30% protein and 12% lipid) obtained after the processes is high enough to use this yeast in the production of animal feed.

CONCLUSIONS

The use of waste glycerol for the production of polyols as well as utilization of the biomass obtained after the process for the production of feed are part of the development of modern waste-free technologies.

Enhanced Cadaverine Production by Engineered Escherichia coli Using Soybean Residue Hydrolysate (SRH) as a Sole Nitrogen Source

An economical source of nitrogen is one of the major limiting factors for sustainable cadaverine production. The utilization potential of soybean residue for enhanced cadaverine production by engineered Escherichia coli DFC1001 was investigated in this study. The SRH from soybean residue could get the protein extraction rate (PE) of 67.51% and the degree of protein hydrolysis (DH) of 22.49%. The protein molecular weights in SRH were mainly distributed in 565 Da (72.28%) and 1252 Da (17.11%). These proteins with small molecular weights and concentrated molecular weight distribution were favorable to be transformed by engineered E. coli DFC1001, and then SRH replaced completely yeast powder as an only nitrogen source for cadaverine production. The maximum cadaverine productivity was 0.52 g/L/h, achieved with a constant speed feeding strategy in the optimized SRH fermentation medium containing an initial total sugar concentration of 30 g/L and exogenous added minerals, which indicated that soybean residue could be a potential feedstock for economic cadaverine production.

Bioreactor production of 2,3-butanediol by Pantoea agglomerans using soybean hull acid hydrolysate as substrate

Production of 2,3-butanediol (2,3-BD) by Pantoea agglomerans strain BL1 was investigated using soybean hull hydrolysate as substrate in batch reactors. The cultivation media consisted of a mixture of xylose, arabinose, and glucose, obtained from the hemicellulosic fraction of the soybean hull biomass. We evaluated the influence of oxygen supply, pH control, and media supplementation on the growth kinetics of the microorganism and on 2,3-BD production. P. agglomerans BL1 was able to simultaneously metabolize all three monosaccharides present in the broth, with average conversions of 75% after 48 h of cultivation. The influence of aeration conditions employed demonstrated the mixed acid pathway of 2,3-BD formation by enterobacteria. Under fully aerated conditions (2 vvm of air), up to 14.02 g L-1 of 2.3-BD in 12 h of cultivation were produced, corresponding to yields of 0.53 g g-1 and a productivity of 1.17 g L-1 h-1, the best results achieved. These results suggest the production potential of 2,3-BD by P. agglomerans BL1, which has been recently isolated from an environmental consortium. The present work proposes a solution for the usage of the hemicellulosic fraction of agroindustry biomasses, carbohydrates whose utilization are not commonly addressed in bioprocess.

Valorisation of pectin-rich agro-industrial residues by yeasts: potential and challenges

Pectin-rich agro-industrial residues are feedstocks with potential for sustainable biorefineries. They are generated in high amounts worldwide from the industrial processing of fruits and vegetables. The challenges posed to the industrial implementation of efficient bioprocesses are however manyfold and thoroughly discussed in this review paper, mainly at the biological level. The most important yeast cell factory platform for advanced biorefineries is currently Saccharomyces cerevisiae, but this yeast species cannot naturally catabolise the main sugars present in pectin-rich agro-industrial residues hydrolysates, in particular d-galacturonic acid and l-arabinose. However, there are non-Saccharomyces species (non-conventional yeasts) considered advantageous alternatives whenever they can express highly interesting metabolic pathways, natively assimilate a wider range of carbon sources or exhibit higher tolerance to relevant bioprocess-related stresses. For this reason, the interest in non-conventional yeasts for biomass-based biorefineries is gaining momentum. This review paper focuses on the valorisation of pectin-rich residues by exploring the potential of yeasts that exhibit vast metabolic versatility for the efficient use of the carbon substrates present in their hydrolysates and high robustness to cope with the multiple stresses encountered. The major challenges and the progresses made related with the isolation, selection, sugar catabolism, metabolic engineering and use of non-conventional yeasts and S. cerevisiae-derived strains for the bioconversion of pectin-rich residue hydrolysates are discussed. The reported examples of value-added products synthesised by different yeasts using pectin-rich residues are reviewed.

Key Points • Review of the challenges and progresses made on the bioconversion of pectin-rich residues by yeasts. • Catabolic pathways for the main carbon sources present in pectin-rich residues hydrolysates. • Multiple stresses with potential to affect bioconversion productivity. • Yeast metabolic engineering to improve pectin-rich residues bioconversion.

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.

Aspergillus niger production of pectinase and α-galactosidase for enzymatic soy processing

Soybean is a most promising sustainable protein source for feed and food to help meet the protein demand of the rapidly rising global population. To enrich soy protein, the environment-friendly enzymatic processing requires multiple carbohydrases including cellulase, xylanase, pectinase, α-galactosidase and sucrase. Besides enriched protein, the processing adds value by generating monosaccharides that are ready feedstock for biofuel/bioproducts. Aspergillus could produce the required carbohydrases, but with deficient pectinase and α-galactosidase. Here we address this critical technological gap by focused evaluation of the suboptimal productivity of pectinase and α-galactosidase. A carbohydrases-productive strain A. niger (NRRL 322) was used with soybean hull as inducing substrate. Temperatures at 20 °C, 25 °C and 30 °C were found to affect cell growth on sucrose with an Arrhenius-law activation energy of 28.7 kcal/mol. The 30 °C promoted the fastest cell growth (doubling time = 2.1 h) and earliest enzyme production, but it gave lower final enzyme yield due to earlier carbon-source exhaustion. The 25 °C gave the highest enzyme yield. pH conditions also strongly affected enzyme production. Fermentations made with initial pH of 6 or 7 were most productive, e.g., giving 1.9- to 2.3-fold higher pectinase and 2.2- to 2.3-fold higher α-galactosidase after 72 h, compared to the fermentation with a constant pH 4. Further, pH must be kept above 2.6 to avoid limitation in pectinase production and, in the later substrate-limiting stage, kept below 5.5 to avoid pectinase degradation. α-Galactosidase production always followed the pectinase production with a 16-24 h lag; presumably, the former relied on pectin hydrolysis for inducers generation. Optimal enzyme production requires controlling the transient availability of inducers.