Reprint of: Effect of fermentation parameters, elicitors and precursors on camptothecin production from the endophyte Fusarium solani

Contribution of endophytes towards improving plant bioactive metabolites: a rescue option against red-taping of medicinal plants

Medicinal plants remain a valuable source for natural drug bioprospecting owing to their multi-target spectrum. However, their use as raw materials for novel drug synthesis has been greatly limited by unsustainable harvesting leading to decimation of their wild populations coupled with inherent low concentrations of constituent secondary metabolites per unit mass. Thus, adding value to the medicinal plants research dynamics calls for adequate attention. In light of this, medicinal plants harbour endophytes which are believed to be contributing towards the host plant survival and bioactive metabolites through series of physiological interference. Stimulating secondary metabolite production in medicinal plants by using endophytes as plant growth regulators has been demonstrated to be one of the most effective methods for increasing metabolite syntheses. Use of endophytes as plant growth promotors could help to ensure continuous supply of medicinal plants, and mitigate issues with fear of extinction. Endophytes minimize heavy metal toxicity in medicinal plants. It has been hypothesized that when medicinal plants are exposed to harsh conditions, associated endophytes are the primary signalling channels that induce defensive reactions. Endophytes go through different biochemical processes which lead to activation of defence mechanisms in the host plants. Thus, through signal transduction pathways, endophytic microorganisms influence genes involved in the generation of secondary metabolites by plant cells. Additionally, elucidating the role of gene clusters in production of secondary metabolites could expose factors associated with low secondary metabolites by medicinal plants. Promising endophyte strains can be manipulated for enhanced production of metabolites, hence, better probability of novel bioactive metabolites through strain improvement, mutagenesis, co-cultivation, and media adjustment.

Enhanced podophyllotoxin production of endophyte Fusarium proliferatum TQN5T by host extract and phenylalanine

Fermentation technology using endophytes is considered a potential alternative approach for producing pharmaceutical compounds like podophyllotoxin (PTOX). In this study, fungus TQN5T (VCCM 44284) was selected from endophytic fungi isolated from Dysosma versipellis in Vietnam for PTOX production through TLC. The presence of PTOX in TQN5T was further confirmed by HPLC. Molecular identification indicated TQN5T as Fusarium proliferatum with 99.43% identity. This result was asserted by morphological characteristics such as white cottony, filamentous colony, layer and branched mycelium, and clear hyphae septa. Cytotoxic assay indicated both biomass extract and culture filtrate of TQN5T presented strong cytotoxicity on LU-1 and HepG2 with IC50 of 0.11, 0.20, 0.041, and 0071, respectively, implying anti-cancer compounds were accumulated in the mycelium and secreted into the medium. Further, the production of PTOX in TQN5T was investigated in the fermentation condition supplemented with 10 µg/ml of host plant extract or phenylalanine as elicitors. The results revealed a significantly higher amount of PTOX in the PDB + PE and PDB + PA at all studied time points in comparison with PDB (control). Especially, after 168 h of culture, PTOX content in the PDB with plant extract reached the peak with 314 µg/g DW which is 10% higher than the best yield of PTOX in previous studies, denoting F. proliferatum TQN5T as a promising PTOX producer. This is the first study on enhancing the PTOX production in endophytic fungi by supplementing phenylalanine-a precursor for PTOX biosynthesis in plants into fermented media, suggesting a common PTOX biosynthetic pathway between host plant and endophytes. KEY POINTS: • Fusarium proliferatum TQN5T was proven for PTOX production. • Both mycelia extract and spent broth extract of Fusarium proliferatum TQN5T presented strong cytotoxicity on cancer cell lines LU-1 and HepG2. • The supplementation of 10 µg/ml host plant extract and phenylalanine into fermentation media of F. proliferatum TQN5T improved the yield of PTOX.

Improved Chrysin Production by a Combination of Fermentation Factors and Elicitation from Chaetomium globosum

Flavonoids encompass a heterogeneous group of secondary metabolites with exceptional health benefits. Chrysin, a natural dihydroxyflavone, possesses numerous bioactive properties, such as anticancer, antioxidative, antidiabetic, anti-inflammatory, etc. However, using traditional sources of chrysin involves extracting honey from plants, which is non-scalable, unsustainable, and depends on several factors, including geography, climatic conditions, and the season, which limits its production at a larger scale. Recently, microbial production of desirable metabolites has garnered attention due to the cost-effectiveness, easy scale-up, sustainability, and low emission of waste. We previously reported for the first time the chrysin-producing marine endophytic fungus Chaetomium globosum, associated with a marine green alga. To extend our understanding of chrysin biosynthesis in C. globosum, in the present study, we have assessed the presence of flavonoid pathway intermediates in C. globosum extracts using LC-MS/MS. The presence of several key metabolites, such as dihydrokaempferol, chalcone, galangin, baicalein, chrysin, p-Coumaroyl-CoA, and p-Cinnamoyl-CoA, indicates the role of flavonoid biosynthesis machinery in the marine fungus. Further, we have aimed to enhance the production of chrysin with three different strategies: (1) optimizing the fermentation parameters, namely, growth medium, incubation time, pH, and temperature; (2) feeding key flavonoid pathway intermediates, i.e., phenylalanine and cinnamic acid; (3) elicitation with biotic elicitors, such as polysaccharide, yeast extract, and abiotic elicitors that include UV radiation, salinity, and metal stress. The combined effect of the optimized parameters resulted in a 97-fold increase in the chrysin yield, resulting in a fungal cell factory. This work reports the first approach for enhanced production of chrysin and can serve as a template for flavonoid production enhancement using marine endophytic fungi.

In Vitro Efficacy of Extracts and Isolated Bioactive Compounds from Ascomycota Fungi in the Treatment of Colorectal Cancer: A Systematic Review

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths worldwide. Despite the advances and success of current treatments (e.g., chemotherapy), there are multiple serious side effects which require the development of new treatment strategies. In recent years, fungi have gained considerable attention as a source of extracts and bioactive compounds with antitumor capabilities because of their antimicrobial and antioxidant properties and even their anti-inflammatory and antiviral activities. In the present review, a systematic search of the existing literature in four electronic databases was carried out in which the antitumor activity against CRC cells of Ascomycota fungi extracts or compounds was tested. The systematical research in the four databases resulted in a total of 883 articles. After applying exclusion and inclusion criteria, a total of 75 articles were finally studied. The order Eurotiales was the most studied (46% of the articles), and the ethyl acetate extraction was the most used method (49% of the papers). Penicillium extracts and gliotoxin and acetylgliotoxin G bioactive compounds showed the highest cytotoxic activity. This review also focuses on the action mechanisms of the extracts and bioactive compounds of fungi against CRC, which were mediated by apoptosis induction and the arrest of the cell cycle, which induces a notable reduction in the CRC cell proliferation capacity, and by the reduction in cell migration that limits their ability to produce metastasis. Thus, the ability of fungi to induce the death of cancer cells through different mechanisms may be the basis for the development of new therapies that improve the current results, especially in the more advanced stages of the CCR.

Exploiting endophytic microbes as micro-factories for plant secondary metabolite production

Plant secondary metabolites have significant potential applications in a wide range of pharmaceutical, food, and cosmetic industries by providing new chemistries and compounds. However, direct isolation of such compounds from plants has resulted in over-harvesting and loss of biodiversity, currently threatening several medicinal plant species to extinction. With the breakthrough report of taxol production by an endophytic fungus of Taxus brevifolia, a new era in natural product research was established. Since then, the ability of endophytic microbes to produce metabolites similar to those produced by their host plants has been discovered. The plant "endosphere" represents a rich and unique biological niche inhabited by organisms capable of producing a range of desired compounds. In addition, plants growing in diverse habitats and adverse environmental conditions represent a valuable reservoir for obtaining rare microbes with potential applications. Despite being an attractive and sustainable approach for obtaining economically important metabolites, the industrial exploitation of microbial endophytes for the production and isolation of plant secondary metabolites remains in its infancy. The present review provides an updated overview of the prospects, challenges, and possible solutions for using microbial endophytes as micro-factories for obtaining commercially important plant metabolites.Key points• Some "plant" metabolites are rather synthesized by the associated endophytes.• Challenges: Attenuation, silencing of BGCs, unculturability, complex cross-talk.• Solutions: Simulation of in planta habitat, advanced characterization methods.

Extending the Metabolite Diversity of the Endophyte Dimorphosporicola tragani

Fungi are one of the most prolific sources of microbial secondary metabolites. The production of new metabolites can be achieved using multiple fermentation conditions and by adding small-molecule effectors, including epigenetic modifiers. In the framework of our Natural Product screening programme targeting the discovery of new antimicrobial compounds, we applied multiple fermentation conditions and adsorptive polymeric resins on a large collection of fungal endophytes, to increase and stimulate their fungal secondary metabolite production. During this work the endophytic fungus Dimorphosporicola tragani CF-090383 showed antimicrobial activity only when grown in presence of adsorptive polymeric resins. In addition, seven epigenetic modifiers were added to fermentations of this endophytic fungus, in an attempt to activate its cryptic pathways as well as to analyse the metabolites produced under these conditions. D. tragani was seen to produce three different mycotoxin dendrodolides when the epigenetic modifiers 5-azacytidine and valproic acid were added to the fermentations, and these compounds were further characterized. However, the fungus produced the fatty acid synthesis inhibitor cerulenin, a molecule not previously described to be produced by this fungal species, only when cultivated in presence of the XAD-16 resin. We have found that the addition of XAD-16 resin resulted in four-fold higher titers in the production of cerulenin when compared to the best production conditions described in literature for the original fungal producer strain, Cephalosporium caerulens KF-140 (=Sarocladium oryzae), in a zeolite-based fermentation, used as an ammonium ion-trapping agent. The production of cerulenin by this strain of D. tragani, represents an alternative source for the improved production of cerulenin with better yields.

Bioprospecting endophytic fungi from Fusarium genus as sources of bioactive metabolites

Endophytic fungi became an attractive source for the discovery of new leads, because of the complexity and the structural diversity of their secondary metabolites. The genus Fusarium comprising about 70 species is extremely variable in terms of genetics, biology, ecology, and consequently, secondary metabolism and have been isolated from countless plants genera from diverse habitats. These endophytic microbes may provide protection and survival strategies in their host plants with production of a repertoire of chemically diverse and structurally unprecedented secondary metabolites reported to exhibit an incredible array of biological activities including antimicrobial, anticancer, antiviral, antioxidants, antiparasitics, immunosuppressants, immunomodulatory, antithrombotic, and biocontrol ability against plants pathogens and nematodes. This review comprehensively highlights over the period 1981-2019, the bioactive potential of metabolites produced by endophytes from Fusarium genus. Abbreviations: AIDS: Acquired immune deficiency syndrome; BAPT: C-13 phenylpropanoid side chain-CoA acyltransferase; CaBr2: Calcium bromide; DBAT: 10-deacetylbaccatin III-10-O-acetyl transferase; DNA: Deoxyribonucleic acid; EI-MS: Electron ionization mass spectrometer; EN: Enniatin; ERK: Extracellular regulated protein kinase; EtOAc: Ethyl acetate; FDA: Food and Drug Administration; GAE/g: Gallic acid equivalent per gram; GC-MS: Gas chromatography-mass spectrometry; HA: Hyperactivation; HCV: Hepatitis C Virus; HCVPR: Hepatitis C Virus protease; HeLa: Human cervical cancer cell line; HIV: Human immunodeficiency viruses; HPLC: High Performance Liquid Chromatography; IAA: Indole-3-acetic acid; IARC: International Agency for Research on Cancer; IC50: Half maximal inhibitory concentration; LC50: Concentration of the compound that is lethal for 50% of exposed population; LC-MS: Liquid chromatography-mass spectrometry; MCF-7: Human breast cancer cell line; MDR: Multidrug-resistant; MDRSA: Multidrug-resistant S. aureus; MFC: Minimum fungicidal concentration; MIC: Minimum inhibitory concentration; MRSA: Multidrug-resistant S. aureus; MTCC: Microbial type culture collection; PBMCs: Peripheral blood mononuclear cells; PCR: Polymerase chain reaction; TB: Tuberculosis; TLC: Thin layer chromatography; TNF: Tumor necrosis factor; WHO: World Health Organization http://www.zoobank.org/urn:lsid:zoobank.org:pub:D0A7B2D8-5952-436D-85C8-C79EAAD1013C.

Production of bioproducts by endophytic fungi: chemical ecology, biotechnological applications, bottlenecks, and solutions

Endophytes are microorganisms that colonize the interior of host plants without causing apparent disease. They have been widely studied for their ability to modulate relationships between plants and biotic/abiotic stresses, often producing valuable secondary metabolites that can affect host physiology. Owing to the advantages of microbial fermentation over plant/cell cultivation and chemical synthesis, endophytic fungi have received significant attention as a mean for secondary metabolite production. This article summarizes currently reported results on plant-endophyte interaction hypotheses and highlights the biotechnological applications of endophytic fungi and their metabolites in agriculture, environment, biomedicine, energy, and biocatalysts. Current bottlenecks in industrial development and commercial applications as well as possible solutions are also discussed.

Metabolic engineering of yeast for fermentative production of flavonoids

Yeast Saccharomyces cerevisiae was engineered for de novo production of six different flavonoids (naringenin, liquiritigenin, kaempferol, resokaempferol, quercetin, and fisetin) directly from glucose, without supplementation of expensive intermediates. This required reconstruction of long biosynthetic pathways, comprising up to eight heterologous genes from plants. The obtained titers of kaempferol 26.57±2.66mgL^-1 and quercetin 20.38±2.57mgL^-1 exceed the previously reported titers in yeast. This is also the first report of de novo biosynthesis of resokaempferol and fisetin in yeast. The work demonstrates the potential of flavonoid-producing yeast cell factories.