In situ high-valued utilization and transformation of sugars from Dioscorea zingiberensis C.H. Wright for clean production of diosgenin

Identification of genetic variants controlling diosgenin content in Dioscorea zingiberensis tuber by genome-wide association study

BACKGROUND

Diosgenin is an important steroidal precursor renowned for its diverse medicinal uses. It is predominantly sourced from Dioscorea species, particularly Dioscorea zingiberensis. Dioscorea zingiberensis has an ability to accumulate 2-16% diosgenin in its rhizomes. In this study, a diverse population of 180 D. zingiberensis accessions was used to evaluate the genomic regions associated with diosgenin biosynthesis by the genome wide association study approach (GWAS).

RESULTS

The whole population was characterized for diosgenin contents from tubers by gas chromatography mass spectrometry. The individuals were genotyped by the genotyping-by-sequencing approach and 10,000 high-quality SNP markers were extracted for the GWAS. The highest significant marker-trait-association was observed as an SNP transversion (G to T) on chromosome 10, with 64% phenotypic variance explained. The SNP was located in the promoter region of CYP94D144 which is a member of P450 gene family involved in the independent biosynthesis of diosgenin from cholesterol. The transcription factor (TF) binding site enrichment analysis of the promoter region of CYP94D144 revealed NAC TF as a potential regulator. The results were further validated through expression profiling by qRT-PCR, and the comparison of high and low diosgenin producing hybrids obtained from a bi-parental population.

CONCLUSIONS

This study not only enhanced the understanding of the genetic basis of diosgenin biosynthesis but also serves as a valuable reference for future genomic investigations on CYP94D144, with the aim of augmenting diosgenin production in yam tubers.

Research progress of diosgenin extraction from Dioscorea zingiberensis C. H. Wright: Inspiration of novel method with environmental protection and efficient characteristics

Diosgenin was the starting materials to synthesize various hormone drugs and mainly generated from Dioscorea zingiberensis C. H. Wright by acidolysis, enzymolysis, microbiological fermentation, and integrated manner. Only acidic hydrolysis with strong acid such as hydrochloric acid or sulfuric acid was used in practice in diosgenin enterprises due to their feasibility and simplicity, nevertheless finally resulting in a great deal of unmanageable wastewater and severely polluted the surrounding environment. Aiming to provide a comprehensive and up-to date information of researches on diosgenin production from this plant, 151 cases were collected from scientific databases including Web of Science, Pubmed, Science Direct, Wiley, Springer, and China Knowledge Resource Integrated (CNKI). Their advantages and disadvantages with different production methods were analyzed based on these available data in this review paper. Considering the fact that nearly all of diosgenin enterprises were closed for the environmental protection and the life health of the people, this review paper was beneficial for providing useful guidelines to develop novel technologies with environmentally-friendly and cleaner features for diosgenin production or facilitate the transformation of other methods like enzymolysis, microbiological fermentation, or integrated methods from laboratory scale to industry scale.

Effect of exogenous jasmonic acid on physiology and steroidal saponin accumulation in Dioscorea zingiberensis

Dioscorea zingiberensis is a valuable medicinal herb rich in steroidal saponins. To reveal the role of jasmonic acid (JA) on physiology and steroidal saponins accumulation, D. zingiberensis were treated with different concentrations of JA. The antioxidant capacity, photosynthetic parameters, fatty acids and metabolites related to steroidal saponins biosynthesis (phytosterols, diosgenin and steroidal saponins) were examined under JA treatment. The results demonstrated that JA treatment caused a great reduction in MDA, stomatal width, photosynthetic rate and photosynthetic pigment, induced a considerable increase in proline, soluble sugar, soluble protein and antioxidant enzymes (CAT, POD and SOD), and leaded to a significant up-regulation in the expression of genes related to antioxidant system and chlorophyll degradation. Specialized metabolites displayed various changes under different concentrations of JA. The majority of fatty acids exhibited negative responses to JA treatment in leaf and rhizome. In leaf, JA treatment enhanced the accumulation of phytosterols and diosgenin, but decreased the accumulation of steroidal saponins. However, steroidal saponins were mainly accumulated in rhizome and were highly increased by JA treatment. Redundancy analysis illustrated that fatty acids were strongly associated with metabolites related to steroidal saponins. Among all fatty acids, C16:0, C18:1, C18:3, C22:0 and C24:0 contributed most to the variation in metabolites related to steroidal saponin biosynthesis. Overall, JA treatment leaded to an increase in steroidal saponins, but an inhibition of plant growth. Thus, the negative effects of JA application on plant physiology should be carefully assessed before being utilized to increase the production of steroidal saponins in D. zingiberensis.

Identification and a phased pH control strategy of diosgenin bio-synthesized by an endogenous Bacillus licheniformis Syt1 derived from Dioscorea zingiberensis C. H. Wright

Diosgenin is widely used as one precursor of steroidal drugs in pharmaceutical industry. Currently, there is no choice but to traditionally extract diosgenin from Dioscorea zingiberensis C. H. Wright (DZW) or other plants. In this work, an environmentally friendly approach, in which diosgenin can be bio-synthesized by the endophytic bacterium Bacillus licheniformis Syt1 isolated from DZW, is proposed. Diosgenin produced by the strain was identified by high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FTIR). The thermal gravimetric analysis (TGA) showed that the melting point of the diosgenin product was 204 °C. The optical rotation measurement exhibited that the optical rotation was α²⁰₅₈₉ =  - 126.1° ± 1.5° (chloroform, c = 1%): negative sign means that the product is left-handed, which is very important to further produce steroid hormone drugs. Cholesterol may be the intermediate product in the diosgenin biosynthesis pathway. In the batch fermentation process to produce diosgenin using the strain, pH values played an important role. A phased pH control strategy from 5.5 to 7.5 was proved to be more effective to improve production yield than any single pH control, which could get the highest diosgenin yield of 85 ± 8.6 mg L^-1. The proposed method may replace phyto-chemistry extraction to produce diosgenin in the industry in the future.Key points• An endophytic Bacillus licheniformis Syt1 derived from host can produce diosgenin.• A dynamic pH industrial control strategy is better than any single pH control.• Proposed diosgenin-produced method hopefully replaces phyto-chemistry extraction.

High-value utilization of the waste hydrolysate of Dioscorea zingiberensis for docosahexaenoic acid production in Schizochytrium sp

The starch saccharification liquid of Dioscorea zingiberensis tubers (SSLD) is a glucose-rich agro-industrial waste. Herein, SSLD was used as a novel potential carbon source for the biosynthesis of docosahexaenoic acid (DHA) in Schizochytrium sp. to achieve waste recycling and high-value utilization. Component analysis showed that SSLD contains abundant nutrients, such as glucose, amino acids, phenolics and flavonoids. When the total sugar concentration in SSLD was optimized to 90 g/L, the biomass and DHA yield reached 44.85 and 6.60 g/L, respectively, which were 32.1% and 36.92% higher than that at pure glucose culture condition. Fermentation characteristics and gene expression analysis showed that SSLD could remarkably improve cell antioxidant capacity, which is beneficial to scavenge intracellular reactive oxygen species and increase the gene expression of antioxidant enzymes in Schizochytrium sp. Hence, SSLD is an effective and economic carbon source for DHA production in Schizochytrium sp.

Increased Extracellular Saponin Production after the Addition of Rutin in Truffle Liquid Fermentation and Its Antioxidant Activities

Saponins possess a variety of pharmacological effects and exhibit great potential in the food industry as bioactive substances. In this study, extracellular saponin production via the liquid fermentation of Tuber melanosporum occurred with the addition of rutin. For this purpose, medium composition and culture conditions were optimized using single-factor experiments and an orthogonal experiment design. The optimal medium consisted of glucose (43.5 g/L), peptone (6 g/L), KH2PO4 (1.15 g/L), NaCl (0.2 g/L), vitamin B2 (0.082 g/L), vitamin B6 (0.1 g/L), vitamin C (0.02 g/L), and rutin (4.8 g/L). The culture conditions were as follows: 12.5% (v/v) inoculation, medium volume of 50 mL/250 mL flask, culture temperature of 24 °C, shaker speed of 190 rpm, initial pH of 5.7, and culture time of 96 h. Finally, a maximal extracellular saponin content of 0.413 g/L was obtained, which was 134.7% higher than that in the base medium. Rutin proved to be an excellent promoter, because the saponin production was increased by 50.2% compared to that in the optimized medium without rutin. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity, hydroxyl radical scavenging activity, and ferric reducing antioxidant power of truffle saponins reached 94.13%, 79.26%, and 42.22 mM, respectively. This study provides a useful strategy for fungal bioactive saponin production by liquid fermentation with the addition of flavonoid compounds.

The origin and evolution of the diosgenin biosynthetic pathway in yam

Diosgenin, mainly produced by Dioscorea species, is a traditional precursor of most hormonal drugs in the pharmaceutical industry. The mechanisms that underlie the origin and evolution of diosgenin biosynthesis in plants remain unclear. After sequencing the whole genome of Dioscorea zingiberensis, we revealed the evolutionary trajectory of the diosgenin biosynthetic pathway in Dioscorea and demonstrated the de novo biosynthesis of diosgenin in a yeast cell factory. First, we found that P450 gene duplication and neo-functionalization, driven by positive selection, played important roles in the origin of the diosgenin biosynthetic pathway. Subsequently, we found that the enrichment of diosgenin in the yam lineage was regulated by CpG islands, which evolved to regulate gene expression in the diosgenin pathway and balance the carbon flux between the biosynthesis of diosgenin and starch. Finally, by integrating genes from plants, animals, and yeast, we heterologously synthesized diosgenin to 10 mg/l in genetically-engineered yeast. Our study not only reveals the origin and evolutionary mechanisms of the diosgenin biosynthetic pathway in Dioscorea, but also introduces an alternative approach for the production of diosgenin through synthetic biology.

Genome survey sequencing of Dioscorea zingiberensis

Dioscorea zingiberensis (Dioscoreceae) is the main plant source of diosgenin (steroidal sapogenins), the precursor for the production of steroid hormones in the pharmaceutical industry. Despite its large economic value, genomic information of the genus Dioscorea is currently unavailable. Here, we present an initial survey of the D. zingiberensis genome performed by next-generation sequencing technology together with a genome size investigation inferred by flow cytometry. The whole genome survey of D. zingiberensis generated 31.48 Gb of sequence data with approximately 78.70× coverage. The estimated genome size is 800 Mb, with a high level of heterozygosity based on K-mer analysis. These reads were assembled into 334 288 contigs with a N50 length of 1079 bp, which were further assembled into 92 163 scaffolds with a total length of 173.46 Mb. A total of 4935 genes, 81 tRNAs, 69 rRNAs, and 661 miRNAs were predicted by the genome analysis, and 263 484 repeated sequences were obtained with 419 372 simple sequence repeats (SSRs). Among these SSRs, the mononucleotide repeat type was the most abundant (up to 54.60% of the total SSRs), followed by the dinucleotide (29.60%), trinucleotide (11.37%), tetranucleotide (3.53%), pentanucleotide (0.65%), and hexanucleotide (0.25%) repeat types. The 1C-value of D. zingiberensis was calibrated against Salvia miltiorrhiza and calculated as 0.87 pg (851 Mb) by flow cytometry, which was very close to the result of the genome survey. This is the first report of genome-wide characterization within this taxon.

Ethanol production from mixtures of sugarcane bagasse and Dioscorea composita extracted residue with high solid loading

Various mixing ratios of alkali pretreated sugarcane bagasse and starch-rich waste Dioscorea composita hemls extracted residue (DER) were evaluated via simultaneous saccharification and fermentation (SSF) with 12% (w/w) solid loading, and the mixture ratio of 1:1 achieved the highest ethanol concentration and yield. When the solid loading was increased from 12% to 32%, the ethanol concentration was increased to 72.04 g/L, whereas the ethanol yield was reduced from 84.40% to 73.71%. With batch feeding and the addition of 0.1% (w/v) Tween 80, the final ethanol concentration and yield of SSF at 34% loading were 82.83 g/L and 77.22%, respectively. Due to the integration with existing starch-based ethanol industry, the co-fermentation is expected to be a competitive alternative form for cellulosic ethanol production.

Isolation of endophytic fungi from Dioscorea zingiberensis C. H. Wright and application for diosgenin production by solid-state fermentation

In this study, endophytic fungi were isolated from Dioscorea zingiberensis C.H. Wright (DZW), and a novel clean process to prepare diosgenin from DZW was developed. A total of 123 strains of endophytic fungi were isolated from different plant tissues of DZW. Among them, the strain Fusarium sp. (CPCC 400709) showed the best activity of hydrolyzing steroidal saponins in DZW into diosgenin. Thus, this strain was used to prepare diosgenin from DZW by solid-state fermentation. The fermentation parameters were optimized using response surface methodology, and a high yield of diosgenin (2.16%) was obtained at 14.5% ammonium sulfate, an inoculum size of 12.3%, and 22 days of fermentation. Furthermore, the highest diosgenin yield (2.79%) was obtained by co-fermentation with Fusarium sp. (CPCC 400709) and Curvularia lunata (CPCC 400737), which was 98.9% of that obtained by β-glucosidase pretreated acid hydrolysis (2.82%). This process is acid-free and wastewater-free, and shows promise as an effective and clean way to prepare diosgenin for use in industrial applications from DZW.

A novel glycosylated solution from Dioscorea zingiberensis C.H. Wright significantly improves the solvent productivity of Clostridium beijerinckii

The economics of bio-solvent production are largely dependent on the cost of the fermentation substrate. Dioscorea zingiberensis C.H. Wright (DZW), the main raw material used to produce saponin, contains 13-18% starch which can be directly saccharified to a saccharification liquid of DZW starch (SLDS) that contains abundant nutrients. In this study, the water-soluble micromolecule compounds in SLDS were quantified through ¹H NMR. Using SLDS as the substrate to conduct ABE fermentation by Clostridium beijerinckii, the fermentation cycle was shortened 24h, the maximum biomass and consumption rate of the glucose significantly increased, and the productivity of total solvents were increased by 0.244±0.010g/L/h compared to standard P₂ medium. Expression analysis of genes encoding key enzymes involved in acetone and butanol production and glucose consumption showed that they were induced by SLDS. Taken together, SLDS is a useful and renewable glycosylated solution for ABE fermentation.

Low pressure steam expansion pretreatment as a competitive approach to improve diosgenin yield and the production of fermentable sugar from Dioscorea zingiberensis C.H. Wright

Development of efficient pretreatment methods which can disrupt the peripheral lignocellulose and even the parenchyma cells is of great importance for production of diosgenin from turmeric rhizomes. It was found that low pressure steam expansion pretreatment (LSEP) could improve the diosgenin yield by more than 40% compared with the case without pretreatment, while simultaneously increasing the production of fermentable sugar by 27.37%. Furthermore, little inhibitory compounds were produced in LSEP process which was extremely favorable for the subsequent biotransformation of fermentable sugar to other valuable products such as ethanol. Preliminary study showed that the ethanol yield when using the fermentable sugar as carbon source was comparable to that using glucose. The liquid residue of LSEP treated turmeric tuber after diosgenin production can be utilized as a quality fermentable carbon source. Therefore, LSEP has great potential in industrial application in diosgenin clean production and comprehensive utilization of turmeric tuber.