New derivatives of the iridoid specioside from fungal biotransformation

De novo biosynthesis of mogroside V by multiplexed engineered yeasts

High sugar intake has become a global health concern due to its association with various diseases. Mogroside V (MG-V), a zero-calorie sweetener with multiple medical properties, is emerging as a promising sugar substitute. However, its application is hindered by low natural abundance and the inefficiency of conventional plant extraction methods. In this study, two glycosyltransferases were introduced into an engineered mogrol-producing Saccharomyces cerevisiae strain to enable the first de novo MG-V biosynthesis. Then, MG-V titer increased by 2.3 × 104-fold through a series of efficient metabolic engineering strategies, including the enhancement of precursors, inhibition of the competitive pathway, and prevention of MG-V degradation. The challenges of enzyme spatial separation and high protein folding stress were addressed through lipid droplet (LD) compartmentalization and endoplasmic reticulum expansion, respectively. The ty1 transposon was employed to increase the copies of LD-targeted fusion protein AtCPR2-CYP87D18, which possessed higher CYP450 catalytic efficiency, resulting in an MG-V titer of 10.25 mg/L in shake flasks and 28.62 mg/L in a 5-L bioreactor. Overall, this study realized de novo MG-V synthesis in S. cerevisiae for the first time and provided a valuable reference for constructing microbial factories for triterpenoid saponin synthesis.

Metabolomic Strategies to Improve Chemical Information from OSMAC Studies of Endophytic Fungi

Metabolomics strategies are important tools to get holistic chemical information from a system, but they are scarcely applied to endophytic fungi to understand their chemical profiles of biosynthesized metabolites. Here Penicillium sp. was cultured using One Strain Many Compounds (OSMAC) conditions as a model system to demonstrate how this strategy can help in understanding metabolic profiles and determining bioactive metabolites with the application of metabolomics and statistical analyses, as well as molecular networking. Penicillium sp. was fermented in different culture media and the crude extracts from mycelial biomass (CEm) and broth (CEb) were obtained, evaluated against bacterial strains (Staphylococcus aureus and Pseudomonas aeruginosa), and the metabolomic profiles by LC-DAD-MS were obtained and chemometrics statistical analyses were applied. The CEm and CEb extracts presented different chemical profiles and antibacterial activities; the highest activities observed were against S. aureus from CEm (MIC = 16, 64, and 128 µg/mL). The antibacterial properties from the extracts were impacted for culture media from which the strain was fermented. From the Volcano plot analysis, it was possible to determine statistically the most relevant features for the antibacterial activity, which were also confirmed from biplots of PCA as strong features for the bioactive extracts. These compounds included 75 (13-oxoverruculogen isomer), 78 (austalide P acid), 87 (austalide L or W), 88 (helvamide), 92 (viridicatumtoxin A), 96 (austalide P), 101 (dihydroaustalide K), 106 (austalide k), 110 (spirohexaline), and 112 (pre-viridicatumtoxin). Thus, these features included diketopiperazines, meroterpenoids, and polyketides, such as indole alkaloids, austalides, and viridicatumtoxin A, a rare tetracycline.

Efficient Synthesis and In Vitro Hypoglycemic Activity of Rare Apigenin Glycosylation Derivatives

Apigenin is a natural flavonoid with significant biological activity, but poor solubility in water and low bioavailability limits its use in the food and pharmaceutical industries. In this paper, apigenin-7-O-β-(6″-O)-d-glucoside (AG) and apigenin-7-O-β-(6″-O-succinyl)-d-glucoside (SAG), rare apigenin glycosyl and succinyl derivatives formed by the organic solvent-tolerant bacteria Bacillus licheniformis WNJ02 were used in a 10.0% DMSO (v/v) system. The water solubility of SAG was 174 times that of apigenin, which solved the application problem. In the biotransformation reaction, the conversion rate of apigenin (1.0 g/L) was 100% at 24 h, and the yield of SAG was 94.2%. Molecular docking showed that the hypoglycemic activity of apigenin, apigenin-7-glucosides (AG), and SAG was mediated by binding with amino acids of α-glucosidase. The molecular docking results were verified by an in vitro anti-α-glucosidase assay and glucose consumption assay of active compounds. SAG had significant anti-α-glucosidase activity, with an IC₅₀ of 0.485 mM and enhanced glucose consumption in HepG2 cells, which make it an excellent α-glucosidase inhibitor.

N-acetylation of toxic aromatic amines by fungi: Strain screening, cytotoxicity and genotoxicity evaluation, and application in bioremediation of 3,4-dichloroaniline

Aromatic amines (AA) are one of the most commonly used classes of compounds in industry and the most common pollutants found in both soil and water. 3,4-Dichloaniline (3,4-DCA) is a persistent residue of the phenylurea herbicide in the environment. In this study, we used a colorimetric method as a new approach to screen 12 filamentous fungal strains of the genera Aspergillus, Chaetomium, Cladosporium, and Mucor to assess their capacity to perform AA N-acetylation since it is considered a potential tool in environmental bioremediation. Subsequently, the selected strains were biotransformed with different AA substrates to evaluate the product yield. The strains Aspergillus niveus 43, Aspergillus terreus 31, and Cladosporium cladosporioides showed higher efficiencies in the biotransformation of 3,4-DCA at 500 µM into its N-acetylated product. These fungal strains also showed great potential to reduce the phytotoxicity of 3,4-DCA in experiments using Lactuca sativa seeds. Furthermore, N-acetylation was shown to be effective in reducing the cytotoxic and genotoxic effects of 3,4-DCA and other AA in the immortalized human keratinocyte (HaCaT) cell line. The isolated products after biotransformation showed that fungi of the genera Aspergillus and Cladosporium appeared to have N-acetylation as the first and main AA detoxification mechanism. Finally, A. terreus 31 showed the highest 3,4-DCA bioremediation potential, and future research can be carried out on the application of this strain to form microbial consortia with great potential for the elimination of toxic AA from the environment.

De novo biosynthesis of rubusoside and rebaudiosides in engineered yeasts

High-sugar diet causes health problems, many of which can be addressed with the use of sugar substitutes. Rubusoside and rebaudiosides are interesting molecules, considered the next generation of sugar substitutes due to their low-calorie, superior sweetness and organoleptic properties. However, their low abundance in nature makes the traditional plant extraction process neither economical nor environmental-friendly. Here we engineer baker's yeast Saccharomyces cerevisiae as a chassis for the de novo production of rubusoside and rebaudiosides. In this process, we identify multiple issues that limit the production, including rate-liming steps, product stress on cellular fitness and unbalanced metabolic networks. We carry out a systematic engineering strategy to solve these issues, which produces rubusoside and rebaudiosides at titers of 1368.6 mg/L and 132.7 mg/L, respectively. The rubusoside chassis strain here constructed paves the way towards a sustainable, large-scale fermentation-based manufacturing of diverse rebaudiosides.