Recent Advances in Yeast Recombinant Biosynthesis of the Triterpenoid Protopanaxadiol and Glycosylated Derivatives Thereof

Plant natural products are a seemingly endless resource for novel chemical structures. However, their extraction often results in high prices, fluctuation in both quantity and quality, and negative environmental impact. The latter might result from the extraction procedure but more often from the high amount of plant biomass required. With the advent of synthetic biology, producing natural plant products in large quantities using yeasts as hosts has become possible. Here, we focus on the recent advances in metabolic engineering of the yeasts species Saccharomyces cerevisiae and Yarrowia lipolytica for the synthesis of ginsenoside triterpenoids, namely, dammarenediol-II, protopanaxadiol, protopanaxatriol, compound K, ginsenoside Rh1, ginsenoside Rh2, ginsenoside Rg3, and ginsenoside F1. A discussion is provided on advanced synthetic biology, bioprocess strategies, and current challenges for the biosynthesis of ginsenoside triterpenoids. Finally, future directions in metabolic and process engineering are summarized and may help reify sustainable ginsenoside production.

Studies on biotransformation mechanism of Fusarium sp. C39 to enhance saponin content of Paridis Rhizoma

Paridis Rhizoma is a natural medicine with strong anti-tumor and anti-inflammatory activities. Our previous research have found that Fusarium sp. C39, an endophytic fungus isolated from Dioscorea nipponica which contains the similar chemical components, significantly increased the steroidal saponins content of Paridis Rhizoma by fermentation. In this study, the inhibitory effects of fermentated Paridis Rhizoma extract (PRE) on liver cancer cells (Hepal-6), cervical cancer cells (Hela), and lung cancer cells (A549) were determined to be stronger than that of the unfermented extract. For discovering the fermentation mechanism of PRE with Fusarium sp. C39, 36 components with obviously quantitative variations were screened out by UPLC-Q/TOF-MS and 53 key genes involved in the metabolic pathways of steroidal saponins were identified by transcriptome. On the basis of comprehensively analyzing information from the metabonomics and transcriptome, it can be speculated that the increase of spirostanol saponins and nuatigenin-type saponins enhanced the inhibitory effect of fermented PRE on cancer cell proliferation. Under the action of glycosidase, glycosyltransferase, oxidoreductases, and genes involved in sterol synthesis, strain C39 achieved the synthesis of diosgenin and the alteration of configurations, sugar chain and substituent of steroidal saponins. The research suggested a microbial transformation approach to increase the resource utilization and activity of Paris polyphylla.

Diversity and Ginsenoside Biotransformation Potential of Cultivable Endophytic Fungi Associated With Panax bipinnatifidus var. bipinnatifidus in Qinling Mountains, China

To obtain novel fungi with potent β-glucosidase for minor ginsenoside production, Panax bipinnatifidus var. bipinnatifidus, which is a traditional medicinal plant containing various ginsenosides, was first employed to isolate endophytic fungi in this study. A total of 93 representative morphotype strains were isolated and identified according to ITS rDNA sequence analyses, and they were grouped into three phyla (Ascomycota, Basidiomycota, and Mucoromycota), five classes (Dothideomycetes, Sordariomycetes, Eurotiomycetes, Agaricomycetes, and Mucoromycetes), and 24 genera. Plectosphaerella (RA, 19.35%) was the most abundant genus, followed by Paraphoma (RA, 11.83%) and Fusarium (RA, 9.70%). The species richness index (S, 34) and the Shannon–Wiener index (H’, 3.004) indicated that P. bipinnatifidus harbored abundant fungal resources. A total of 26 endophytic fungal ethyl acetate extracts exhibited inhibitory activities against at least one pathogenic bacterium or fungus. In total, 11 strains showed strong β-glucosidase activities and also presented with the ability of ginsenoside biotransformation with varied glycoside-hydrolyzing pathways. Excitingly, three genera, namely, Ilyonectria, Sarocladium, and Lecanicillium, and all 11 taxa were first found to have the ability to transform ginsenosides in our study. The results indicated that P. bipinnatifidus could be a new fungi resource with potential novel natural compounds with antimicrobial activity and potent β-glucosidase for varied minor ginsenoside production.

Bacterial endophytes from ginseng and their biotechnological application

Ginseng has been well-known as a medicinal plant for thousands of years. Bacterial endophytes ubiquitously colonize the inside tissues of ginseng without any disease symptoms. The identification of bacterial endophytes is conducted through either the internal transcribed spacer region combined with ribosomal sequences or metagenomics. Bacterial endophyte communities differ in their diversity and composition profile, depending on the geographical location, cultivation condition, and tissue, age, and species of ginseng. Bacterial endophytes have a significant effect on the growth of ginseng through indole-3-acetic acid (IAA) and siderophore production, phosphate solubilization, and nitrogen fixation. Moreover, bacterial endophytes can protect ginseng by acting as biocontrol agents. Interestingly, bacterial endophytes isolated from Panax species have the potential to produce ginsenosides and bioactive metabolites, which can be used in the production of food and medicine. The ability of bacterial endophytes to transform major ginsenosides into minor ginsenosides using β-glucosidase is gaining increasing attention as a promising biotechnology. Recently, metabolic engineering has accelerated the possibilities for potential applications of bacterial endophytes in producing beneficial secondary metabolites.

Cordyceps sinensis-mediated biotransformation of notoginsenoside R1 into 25-OH-20(S/R)-R2 with elevated cardioprotective effect against DOX-induced cell injury

Notoginsenoside R1 is a dammarane saponin in Panax notoginseng with promising cardioprotective effects. The bioactivity–structure relationship of such saponins suggested that the presence of a hydroxyl group at C25 could elevate its performance. To fulfill that goal, bioconversion of notoginsenoside R1 was mediated by a biocatalytic system of Cordyceps sinensis that had successfully produced multiple 25-OH derivatives from ginsenoside Re and Rg1. The major metabolic products of notoginsenoside R1 were identified as 25-OH-20(S/R)-R2 via the techniques of HRMS, ¹³C-NMR, ¹H-NMR, HSQC and HMBC. Time-course experiments were designed to monitor the reaction process, establishing a biocatalytic pathway of “R1→20(S/R)-R2→25-OH-20(S/R)-R2”. The bioconversion rate of these 25-OH derivatives added up to 69.87% which greatly precedes the previous report. Afterwards, the effect of these biocatalytic products against doxorubicin-induced cardiotoxicity was evaluated, indicating a significant increase in efficacy after the hydration of the C24–C25 double bond on the dammarane skeleton. In conclusion, the biocatalytic system employed in this paper is able to harvest 25-OH-20(S/R)-R2 in high yield from notoginsenoside R1, which will provide lead compounds or drug candidates to alleviate myocardial injury caused by doxorubicin.

The biocatalytic system in this paper preferably yielded 25-OH notoginsenoside R2 from R1 in a regioselective manner. Such a process significantly elevated the effects of these 25-OH derivatives against DOX-induced cardiomyocyte injury.

Chitinophaga chungangae sp. nov., isolated from a Korean grape garden and its potential to biosynthesize ginsenoside Rg2

A ginsenoside Rg2-producing, Gram stain-negative, aerobic, catalase and oxidase-positive, rod-shaped, non-motile and orange pigmented novel bacterium designated strain MAH-28 ^T was isolated from soil sample of a grape garden. Strain MAH-28 ^T hydrolyzed aesculin, casein and DNA. Flexirubin-type pigments are present. Phylogenetic analysis based on 16S rRNA gene sequence showed that strain MAH-28 ^T formed a cluster within the genus Chitinophaga and the most close relatives were Chitinophaga alhagiae T22^T (98.9% 16S rRNA gene sequence similarity), Chitinophaga humicola Ktm-2 ^T (98.8%), Chitinophaga barathri YLT18^T (98.3%) and Chitinophaga lutea ZY74^T (97.4%). The novel strain MAH-28 ^T has a draft genome size of 6,043,180 bp (14 contigs), annotated with 4,863 protein-coding genes, 53 tRNA and 6 rRNA genes. The ANI and dDDH values between strain MAH-28 ^T and the closely related type strains were in the range of 76.0-83.4% and 20.3-26.7%, respectively. The novel strain MAH-28 ^T was able to synthesize ginsenoside Rg2 from major ginsenoside Re. The genome annotation revealed 152 carbohydrate genes which may involve with the synthesis of ginsenoside Rg2. The respiratory quinone of strain MAH-28 ^T was MK-7 and the dominant cellular fatty acids were C_{15:0 iso}, C_16:1 ω5c and C_{17:0 iso} 3-OH. The DNA G + C content of strain MAH-28 ^T was 53.3 mol%. Based on the phenotypic, chemotaxonomic and phylogenetic studies, strain MAH-28 ^T represents a new member of genus Chitinophaga for which the name Chitinophaga chungangae sp. nov. is proposed with type strain MAH-28 ^T (= KACC 19968 ^T = CGMCC 1.16605 ^T).

Synthesis, Anti-Tumor Activity and Apoptosis-Inducing Effect of Novel Dimeric Keggin-Type Phosphotungstate

A dimeric Keggin-type phosphotungstate (ODA)₁₀[(PW₁₁FeO₃₉)₂O]·9H₂O (abbreviated as ODA₁₀[(PW₁₁Fe)₂], ODA = octadecyltrimethylammonium bromide) was synthesized and investigated comprehensively its antitumor activity on MCF-7 and A549 cells. The dimeric structure and amorphous morphology were characterized by FT-IR, UV-vis-DRS, SEM and XRD. The in vitro MTT assay of ODA₁₀[(PW₁₁Fe)₂] showed anticancer activity on MCF-7 and A549 cells in a dose- and time-dependent manner, and the IC₅₀ values for MCF-7 and A549 cells at 48 h were 5.83 μg/ml and 3.23 μg/ml, respectively. The images of the ODA₁₀[(PW₁₁Fe)₂]-treated cells observed by inverted biological microscope exhibited the characteristic morphology of apoptosis. Flow cytometric analysis showed cell apoptosis and cycle arrested at S phase induced by ODA₁₀[(PW₁₁Fe)₂]. The above results illuminated the main mechanism of the antitumor action of ODA₁₀[(PW₁₁Fe)₂] on MCF-7 and A549 cells, indicating that this dimeric phosphotungstate is a promising anticancer drug.