A Mixed Culture of Endophytic Fungi Increases Production of Antifungal Polyketides

An Update of Fungal Endophyte Diversity and Strategies for Augmenting Therapeutic Potential of their Potent Metabolites: Recent Advancement

Endophytic fungi represent a significant renewable resource for the discovery of pharmaceutically important compounds, offering substantial potential for new drug development. Their ability to address the growing issue of drug resistance has drawn attention from researchers seeking novel, nature-derived lead molecules that can be produced on a large scale to meet global demand. Recent advancements in genomics, metabolomics, bioinformatics, and improved cultivation techniques have significantly aided the identification and characterization of fungal endophytes and their metabolites. Current estimates suggest there are approximately 1.20 million fungal endophytes globally, yet only around 16% (190,000) have been identified and studied in detail. This underscores the vast untapped potential of fungal endophytes in pharmaceutical research. Research has increasingly focused on the transformation of bioactive compounds by fungal endophytes through chemical and enzymatic processes. A notable example is the anthraquinone derivative 6-O-methylalaternin, whose cytotoxic potential is enhanced by the addition of a hydroxyl group, sharing structural similarities with its parent compound macrosporin. These structure-bioactivity studies open up new avenues for developing safer and more effective therapeutic agents by synthesizing targeted derivatives. Despite the immense promise, challenges remain, particularly in the large-scale cultivation of fungal endophytes and in understanding the complexities of their biosynthetic pathways. Additionally, the genetic manipulation of endophytes for optimized metabolite production is still in its infancy. Future research should aim to overcome these limitations by focusing on more efficient cultivation methods and deeper exploration of fungal endophytes' genetic and metabolic capabilities to fully harness their therapeutic potential.

A mass spectrometry-based strategy for investigating volatile molecular interactions in microbial consortia: unveiling a Fusarium-specific induction of an antifungal compound

Co-cultivation of microorganisms has emerged as a promising methodology for deciphering the intricate molecular interactions between species. This approach facilitates the replication of natural niches of ecological or clinical relevance where microbes consistently interact. In this context, increasing attention has been addressed toward elucidating the molecular crosstalk within fungal co-cultures. However, a major challenge in this area of research is determining the fungal origin of metabolites induced in co-cultivation systems. Molecules elicited in co-cultures may not be detectable in the individual cultures, making it challenging to establish which microorganism is responsible for their induction. For agar-diffused metabolites, imaging mass spectrometry can help overcome this obstacle by localizing the induced molecules during fungal confrontations. For volatile metabolites, however, this remains an open problem. To address this issue, in this study, a three-head-to-head co-culture strategy was developed, specifically focusing on the exploration of volatile interactions between fungi via headspace solid-phase microextraction combined with gas chromatography mass spectrometry. This methodology was applied to study the volatile molecular interactions of three fungal species: Fusarium culmorum, Aspergillus amstelodami, and Cladosporium cladosporioides. The adopted strategy revealed a Fusarium-specific induction of three volatile molecules: γ-terpinene and two unidentified sesquiterpene compounds. Interestingly, γ-terpinene showed antifungal activity in a bioassay against the other two fungal species: Aspergillus amstelodami and Cladosporium cladosporioides. The proposed methodology could help to investigate volatile molecular interactions and highlight metabolite induction specific to a particular fungus involved in in vitro fungal confrontations. This is relevant for a better understanding of the complex biosynthetic responses of fungi in consortia and for identifying volatile molecules with antifungal activity.

Endophytic Fungi Co-Culture: An Alternative Source of Antimicrobial Substances

Antimicrobial resistance is becoming a critical issue due to the widespread and indiscriminate use of antibiotics and antifungals to treat common infections, leading to a growing shortage of effective drugs. Moreover, the increase in antimicrobial resistance is enhancing the pathogenicity and virulence of various pathogens. Microorganisms are key sources of chemically diverse specialized metabolites, which are produced in the final stages of their growth cycle. These metabolites hold significant value in chemical, pharmaceutical, and agrochemical industries. One of the major challenges researchers face in this field is the frequent isolation of already-known substances when classical protocols are used. To address this, several innovative strategies have been developed. The co-culture approach is a powerful tool for activating silent biosynthetic gene clusters, as it simulates natural microbial environments by creating artificial microbial communities. This method has shown promising results, with new compounds being isolated and the yields of target substances being improved. In this context, this review provides examples of antimicrobial compounds obtained from co-cultures of endophytic fungi, conducted in both liquid and solid media. Additionally, the review discusses the advantages and challenges of the co-culture technique. Significance and Impact of the Study: Microbial co-culture is a valuable strategy for discovering new natural products with antimicrobial activity, as well as for scaling up the production of target substances. This review aims to summarize important examples of endophyte co-cultures and highlights the potential of endophytic fungi co-culture for pharmacological applications.

Untargeted Metabolomic to Access Chemical Differences Induced by Dual Endophyte Cultures Isolated from Euphorbia Umbellata

Endophytic fungi live asymptomatically inside vegetal tissues, and such uncommon habitat contributes to their exceptional chemical diversity. Isolating natural products from endophytic fungi could fail due to silent biosynthetic gene clusters under ordinary in vitro culture conditions, and co-culturing has been assayed to trigger their metabolism. We carried out single and dual cultures with 13 endophyte strains isolated from Euphorbia umbellata leaves. Multivariate statistics applied to untargeted metabolomics compared the chemical profiles of all endophyte cultures. PCA analysis guided the selection of the Aspergillus pseudonomiae J1 - Porogramme brasiliensis J9 dual culture for its most significant chemical differentiation: Five compounds were putatively annotated in the J1-J9 culture according to UHPLC-HRMS data, kojic acid, haliclonol and its diastereoisomer, caffeic acid, and 2-(3,4-dihydroxyphenyl)acetaldehyde. Analysis by PLS-DA using VIP score showed that kojic acid displayed the most significative importance in discriminating single and dual J1-J9 cultures.

Synthesis of an autochthonous microbial community by analyzing the core microorganisms responsible for the critical flavor of bran vinegar

Traditional bran vinegar brewing unfolds through natural fermentation, a process driven by spontaneous microbial activity. The unique metabolic activities of various microorganisms lead to distinct flavors and qualities in each batch of vinegar, making it challenging to consistently achieve the desired characteristic flavor compounds. Therefore, identifying the critical microbial species responsible for flavor production and designing starter cultures with improved fermentation efficiency and characteristic flavors are effective methods to address this discrepancy. In this study, 11 core functional microbial species affecting the fermentation flavor of Sichuan shai vinegar (Cupei were placed outside solarization and night-dew for more than one year, and vinegar was the liquid leached from Cupei) (SSV), were revealed by combining PacBio full-length diversity sequencing based on previous metagenomics. The effects of environmental factors and microbial interactions on the growth of 11 microorganisms during fermentation were verified using fermentation experiments. Ultimately, the microbial community was strategically synthesized using a 'top-down' approach, successfully replicating the distinctive flavor profile of Sichuan shai vinegar (SSV). The results showed that the interaction between microorganisms and environmental factors affected microorganism growth. Compared with traditional fermentation, the synthetic microbial community's vinegar-fermented grains (Cupei) can reproduce the key flavor of SSV and is conducive to the production of amino acids. In this study, the key flavor of SSV was reproduced through rational design of the synthetic microbial community. This achievement holds profound significance for the broader application of microbiome assembly strategies in the realm of fermented foods.

Way to efficient microbial paclitaxel mass production

The microbial synthesis of paclitaxel is attractive for its short-cycle, cost-effectiveness, and sustainability. However, low paclitaxel productivity, depleted capacity during subculture and storage, and unclear biosynthesis mechanisms restrain industrial microbial synthesis. Along with the isolation of various paclitaxel-producing microorganisms and the development of versatile molecular tools, tremendous promises for microbial paclitaxel synthesis have become increasingly prominent. In this review, we summarize the progress of microbial synthesis of paclitaxel in recent years, focusing on paclitaxel-producing endophytes and representative engineering microorganism hosts that were used as chassis for paclitaxel precursor synthesis. Numerous wide-type microbes can manufacture paclitaxel, and fermentation process optimization and strain improvement can greatly enhance the productivity. Engineered microbes can efficiently synthesize precursors of paclitaxel by introducing exogenous synthetic pathway. Mining paclitaxel synthetic pathways and genetic manipulation of endophytes will accelerate the construction of microbial cell factories, indefinitely contributing to paclitaxel mass production by microbes. This review emphasizes the potential and provides solutions for efficient microbial paclitaxel mass production.

Fungal Duel between Penicillium brasilianum and Aspergillus nomius Results in Dual Induction of Miktospiromide A and Kitrinomycin A

Cocultivation of the fungi Penicillium brasilianum MST-FP1927 and Aspergillus nomius MST-FP2004 resulted in the reciprocal induction of two new compounds, miktospiromide A (1) from A. nomius and kitrinomycin A (2) from P. brasilianum. A third new compound, kitrinomycin B (3), was also identified from an axenic culture of P. brasilianum, along with the previously reported compounds austalide K (4), 17S-dihydroaustalide K (5), verruculogen (6), and fumitremorgin B (7). The structures of 1-3 were elucidated by detailed spectroscopic analysis and DFT calculations, while 4-7 were identified by comparison to authentic standards. The genome of A. nomius MST-FP2004 was sequenced, and a putative biosynthetic gene cluster for 1 was identified. Compound 2 showed activity against murine melanoma NS-1 cells (LD99 7.8 μM) and the bovine parasite Tritrichomonas foetus (LD99 4.8 μM).

Antifungal activity of volatile and non-volatile metabolites of endophytes of Chloranthus elatior Sw

Agriculture crops that have fungal infections suffer significant economic losses and reduced crop output. Chemical fungicides are used to tackle the problem, although this has additional detrimental side effects. There is an urgent need for safe and novel antifungals. Volatiles from plant-beneficial endophytic fungi are considered promising alternatives for the biological control of fungal pathogens as a sustainable approach in an agroecosystem. In the present investigation, a volatile-emitting sterile endophytic fungus, Diaporthe sp. CEL3 with bio-fumigation activity, was isolated from leaves of the ethnomedicinal plant Chloranthus elatior Sw., collected from the Passighat forest of North-East India. The camphor odor volatiles of CEL3 showed an inhibitory effect against eight fungal pathogens in vitro and minimized the infections of Monilinia fructicola, a causal agent of cherry fruit rot, in VOC-exposed cherry fruits. Rhizoctonia solani, Botrytis cinerea, Pythium ultimum, and M. fructicola were maximally inhibited up to 51.5%, 55.8%, 61.9%, and 78.5%, respectively, in comparison to control by the volatiles. Another isolate, CEL7, identified as Curvularia sp., synthesized non-volatile, soluble antifungal metabolites in its cell-free extracts and exhibited antifungal action. Bioassay-guided fractionation revealed the presence of imidazole compounds- (2-aminoethyl)-1H-imidazole-2-carbaldehyde, Pyrazole 4, 5 imidazole, 1-formyl 3-ethyl, phenol compounds-Phenol, 4-[2-(methylamino) ethyl]-, 6-Nitro-3-chlorophenol, Phenol, 2,4,6-tri-tert-butyl-, etc., in the cell-free extracts, with a MIC value of 250-2,000 µg ml-1. Optimum VOC emission was achieved in a modified PDA medium with instantly smashed potato (150 g L-1), dextrose (20 g L-1), wheat husk (20 g L-1), and yeast extract (20 g L-1), with additional salts. Interestingly, endophytic CEL3 emitted different types of volatiles, and trans-verbenol (32.25%), geraniol (30.32%), trans-ocimenol (12.90%), and mentha-4,8-diene (5.16%) were the prime ones. These VOCs cause lethal leakage of protein and necessary intracellular molecules from the fungal pathogens. Thus, CEL3 could potentially be used as a bio-fumigating agent to control post-harvest infections caused by fungal pathogens. This study opens a new approach to the use of endophytic fungi in biocontrol.

Deciphering mechanisms of production of natural compounds using inducer-producer microbial consortia

Living organisms produce a wide range of metabolites. Because of their potential antibacterial, antifungal, antiviral, or cytostatic properties, such natural molecules are of high interest to the pharmaceutical industry. In nature, these metabolites are often synthesized via secondary metabolic biosynthetic gene clusters that are silent under the typical culturing conditions. Among different techniques used to activate these silent gene clusters, co-culturing of "producer" species with specific "inducer" microbes is a particularly appealing approach due to its simplicity. Although several "inducer-producer" microbial consortia have been reported in the literature and hundreds of different secondary metabolites with attractive biopharmaceutical properties have been described as a result of co-cultivating inducer-producer consortia, less attention has been devoted to the understanding of the mechanisms and possible means of induction for production of secondary metabolites in co-cultures. This lack of understanding of fundamental biological functions and inter-species interactions significantly limits the diversity and yield of valuable compounds using biological engineering tools. In this review, we summarize and categorize the known physiological mechanisms of production of secondary metabolites in inducer-producer consortia, and then discuss approaches that could be exploited to optimize the discovery and production of secondary metabolites.

The Potential Use of Fungal Co-Culture Strategy for Discovery of New Secondary Metabolites

Fungi are an important and prolific source of secondary metabolites (SMs) with diverse chemical structures and a wide array of biological properties. In the past two decades, however, the number of new fungal SMs by traditional monoculture method had been greatly decreasing. Fortunately, a growing number of studies have shown that co-culture strategy is an effective approach to awakening silent SM biosynthetic gene clusters (BGCs) in fungal strains to produce cryptic SMs. To enrich our knowledge of this approach and better exploit fungal biosynthetic potential for new drug discovery, this review comprehensively summarizes all fungal co-culture methods and their derived new SMs as well as bioactivities on the basis of an extensive literature search and data analysis. Future perspective on fungal co-culture study, as well as its interaction mechanism, is supplied.

Enhancing chemical and biological diversity by co-cultivation

In natural product research, microbial metabolites have tremendous potential to provide new therapeutic agents since extremely diverse chemical structures can be found in the nearly infinite microbial population. Conventionally, these specialized metabolites are screened by single-strain cultures. However, owing to the lack of biotic and abiotic interactions in monocultures, the growth conditions are significantly different from those encountered in a natural environment and result in less diversity and the frequent re-isolation of known compounds. In the last decade, several methods have been developed to eventually understand the physiological conditions under which cryptic microbial genes are activated in an attempt to stimulate their biosynthesis and elicit the production of hitherto unexpressed chemical diversity. Among those, co-cultivation is one of the most efficient ways to induce silenced pathways, mimicking the competitive microbial environment for the production and holistic regulation of metabolites, and has become a golden methodology for metabolome expansion. It does not require previous knowledge of the signaling mechanism and genome nor any special equipment for cultivation and data interpretation. Several reviews have shown the potential of co-cultivation to produce new biologically active leads. However, only a few studies have detailed experimental, analytical, and microbiological strategies for efficiently inducing bioactive molecules by co-culture. Therefore, we reviewed studies applying co-culture to induce secondary metabolite pathways to provide insights into experimental variables compatible with high-throughput analytical procedures. Mixed-fermentation publications from 1978 to 2022 were assessed regarding types of co-culture set-ups, metabolic induction, and interaction effects.

Naturally Occurring Partially Reduced Perylenequinones from Fungi

This Review provides a critical analysis of the literature covering the naturally occurring partially reduced perylenequinones (PQs) from fungi without carbon substituents (which can be named class A perylenequinones) and discusses their structures, stereochemistry, biosynthesis, and biological activities as appropriate. Perylenequinones are natural pigments with a perylene skeleton produced by certain fungi, aphids, some plants, and animal species. These compounds display several biological activities, e.g., antimicrobial, anti-HIV, photosensitizers, cytotoxic, and phytotoxic. It describes 36 fungal PQs and cites 81 references, covering from 1956 to August 2022.

Fungal-fungal co-culture: a primer for generating chemical diversity

Covering: 2002 to 2020In their natural environment, fungi must compete for resources. It has been hypothesized that this competition likely induces the biosynthesis of secondary metabolites for defence. In a quest to discover new chemical diversity from fungal cultures, a growing trend has been to recapitulate this competitive environment in the laboratory, essentially growing fungi in co-culture. This review covers fungal-fungal co-culture studies beginning with the first literature report in 2002. Since then, there has been a growing number of new secondary metabolites reported as a result of fungal co-culture studies. Specifically, this review discusses and provides insights into (1) rationale for pairing fungal strains, (2) ways to grow fungi for co-culture, (3) different approaches to screening fungal co-cultures for chemical diversity, (4) determining the secondary metabolite-producing strain, and (5) final thoughts regarding the fungal-fungal co-culture approach. Our goal is to provide a set of practical strategies for fungal co-culture studies to generate unique chemical diversity that the natural products research community can utilize.

Improvement of beauvericin production by Fusarium oxysporum AB2 under solid-state fermentation using an optimised liquid medium and co-cultures

The production of beauvericin (BEA) by Fusarium oxysporum AB2 in liquid medium (SmF) was compared to that on solid medium (SSF) on inert support (polyurethane foam or PUF), using a previously optimised medium. The analysis included two different concentrations of the medium (1 × and 3 ×). Under SSF, the production of BEA (22.8 mg·L^-1) was higher relative to SmF (0.8 mg·L^-1). The production increased proportionally in the concentrated medium (3 ×) (65.3 mg·L^-1); using the concentrated medium in SmF, the production of BEA was completely inhibited, although more biomass was produced. The peak of BEA production was reached on day 7 and remained stable until day 11; sustained production after several days has not been achieved in similar reports. The presence of BEA was corroborated by high-performance liquid chromatography (HPLC) and mass spectrometry. The BEA production profile is shown performing mixed cultures of Fusarium oxysporum AB2 and Epicoccum nigrum TORT using the same system, increasing the production of BEA up to 84.6 mg·L^-1. We propose SSF using polyurethane foam (PUF) as a solid support as a new culture system for obtaining secondary metabolites such as BEA.

Promotion of the Hypocrellin Yield by a Co-Culture of Shiraia bambusicola (GDMCC 60438) with Arthrinium sp. AF-5 Fungus

Hypocrellin is a natural 3,10-xylene-4,9-anthracene derivative compound that originates from the stroma of Shiraia bambusicola (S. bambusicola) and Hypocrella bambusae with excellent photobiological activities. Submerged fermentation with the mycelia of S. bambusicola is generally regarded as an ideal technology for hypocrellin production. This study developed a co-cultivation strategy for an obvious promotion of the hypocrellin yield by incubating S. bambusicola (GDMCC 60438) with the endophyte fungus Arthrinium sp. AF-5 isolated from the bamboo tissue. The results indicated that the yield of hypocrellin A (HA) reached a 66.75 mg/g carbon source after an 84-h co-cultivation of the two strains, which was a four-time increase of that by the fermentation only with the S. bambusicola. The microscope observation found that the mycelia of the two strains were intertwined with each other to form the mycelium pellets during the co-cultivation. Moreover, the mycelium pellets of the co-culture showed a contracted and slightly damaged morphology. The addition of H2O2 in the fermentation media could further increase the HA production by 18.31%.

Fungal social influencers: secondary metabolites as a platform for shaping the plant-associated community

Fungal secondary metabolites (FSMs) are capable of manipulating plant community dynamics by inhibiting or facilitating the establishment of co-habitating organisms. Although production of FSMs is not crucial for survival of the producer, their absence can indirectly impair growth and/or niche competition of these fungi on the plant. The presence of FSMs with no obvious consequence on the fitness of the producer leaves questions regarding ecological impact. This review investigates how fungi employ FSMs as a platform to mediate fungal-fungal, fungal-bacterial and fungal-animal interactions associated with the plant community. We discuss how the biological function of FSMs may indirectly benefit the producer by altering the dynamics of surrounding organisms. We introduce several instances where FSMs influence antagonistic- or alliance-driven interactions. Part of our aim is to decipher the meaning of the FSM 'language' as it is widely noted to impact the surrounding community. Here, we highlight the contribution of FSMs to plant-associated interaction networks that affect the host either broadly or in ways that may have previously been unclear.

Improvement of the Biosynthesis of Resveratrol in Endophytic Fungus (Alternaria sp. MG1) by the Synergistic Effect of UV Light and Oligomeric Proanthocyanidins

Resveratrol, a natural polyphenol compound with multiple bioactivities, is widely used in food and pharmaceutical industry. Endophytic fungus Alternaria sp. MG1, as a native producer of resveratrol, shows increasing potential application. However, strategies for improvement of the biosynthesis of resveratrol in this species are still scarce. In this study, different elicitors were used to investigate their effect on the biosynthesis of resveratrol in MG1 and the induction mechanism. Ultrasound and sodium butyrate had no effect and slight inhibition on the resveratrol production and related gene expression, respectively. UV radiation and co-culture with Phomopsis sp. XP-8 significantly promoted the biosynthesis of resveratrol with the highest production (240.57μg/l) coming from UV 20min. Co-culture altered the profiles of secondary metabolites in MG1 by promoting and inhibiting the synthesis of stilbene and lignin compounds, respectively, and generating new flavonoids ((+/-)-taxifolin, naringin, and (+)-catechin). Oligomeric proanthocyanidins (OPC) also showed an obviously positive influence, leading to an increase in resveratrol production by 10 to 60%. Two calcium-dependent protein kinases (CDPK) were identified, of which CDPK1 was found to be an important regulatory factor of OPC induction. Synergistic treatment of UV 20min and 100μm OPC increased the production of resveratrol by 70.37% compared to control and finally reached 276.31μg/l.

Evaluation of the Antibacterial Activity of Crude Extracts Obtained From Cultivation of Native Endophytic Fungi Belonging to a Tropical Montane Rainforest in Colombia

Bioactive secondary metabolite production from endophytic fungi has gained a recurring research focus in recent decades as these microorganisms represent an unexplored biological niche for their diverse biotechnological potential. Despite this focus, studies involving tropical endophytes remain scarce, particularly those isolated from medicinal plants of these ecosystems. In addition, the state of the art of the pharmaceutical industry has experienced stagnation in the past 30years, which has pushed pathogenic infections to get one step ahead, resulting in the development of resistance to existing treatments. Here, five fungal endophytes were isolated from the medicinal plant Otoba gracilipes (Myristicaceae), which corresponded to the genera Xylaria and Diaporthe, and screened to demonstrate the promissory potential of these microorganisms for producing bioactive secondary metabolites with broad-spectrum antibacterial activities. Thus, the evaluation of crude organic extracts obtained from the mycelia and exhaust medium allowed the elucidation of Xylaria sp. and Diaporthe endophytica potential toward providing crude extracellular extracts with promising bioactivities against reference strains of Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923), according to the determined half-maximum inhibitory concentration (IC₅₀) with values down to 3.91 and 10.50mg/ml against each pathogen, respectively. Follow-up studies provided insights into the polarity nature of bioactive compounds in the crude extracts through bioactivity guided fractionation using a polymeric resin absorbent alternative extraction procedure. In addition, evaluation of the co-culturing methods demonstrated how this strategy can enhance endophytes biosynthetic capacity and improve their antibacterial potential with a 10-fold decrease in the IC₅₀ values against both pathogens compared to the obtained values in the preliminary evaluations of Xylaria sp. and D. endophytica crude extracts. These results support the potential of Colombian native biodiversity to provide new approaches concerning the global emergence of antibiotics resistance and future production of undiscovered compounds different from the currently used antibiotics classes and simultaneously call for the value of preserving native habitats due to their promising ecosystemic applications in the biotechnological and pharmaceutical industries.

Chemical Ecology in Insect-microbe Interactions in the Neotropics

Small molecules frequently mediate symbiotic interactions between microorganisms and their hosts. Brazil harbors the highest diversity of insects in the world; however, just recently, efforts have been directed to deciphering the chemical signals involved in the symbioses of microorganisms and social insects. The current scenario of natural products research guided by chemical ecology is discussed in this review. Two groups of social insects have been prioritized in the studies, fungus-farming ants and stingless bees, leading to the identification of natural products involved in defensive and nutritional symbioses. Some of the compounds also present potential pharmaceutical applications as antimicrobials, and this is likely related to their ecological roles. Microbial symbioses in termites and wasps are suggested promising sources of biologically active small molecules. Aspects related to public policies for insect biodiversity preservation are also highlighted.

Dynamics of Chemical Diversity during Co-Cultures: An Integrative Time-Scale Metabolomics Study of Fungal Endophytes Cophinforma mamane and Fusarium solani

A rapid and efficient metabolomic study of Cophinforma mamane and Fusarium solani co-cultivation in time-series based analysis was developed to study metabolome variations during their fungal interactions. The fungal metabolomes were studied through the integration of four metabolomic tools: MS-DIAL, a chromatographic deconvolution of liquid-chromatography-mass spectrometry (LC/MS); MS-FINDER, a structure-elucidation program with a wide range metabolome database; GNPS, an effective method to organize MS/MS fragmentation spectra, and MetaboAnalyst, a comprehensive web application for metabolomic data analysis and interpretation. Co-cultures of C. mamane and F. solani induced different patterns of metabolite production over 10 days of incubation and induced production of five de novo compounds not occurring in monocultures. These results emphasize that co-culture in time-frame analysis is an interesting method to unravel hidden metabolome in the investigation of fungal chemodiversity.

Multifarious Elicitors: Invoking Biosynthesis of Various Bioactive Secondary Metabolite in Fungi

Natural products are considered to be the lifeline treatment for several diseases where their structural complexity makes them a source of potential lead molecules. As a producer of antibiotics, food colorants, enzymes, and nutritious food, fungi are beneficial to humans. Fungi, as a source of novel natural products, draw attention of scientists. However, redundant isolation of metabolite retards the rate of discovery. So, apart from the standard conditions for the production of secondary metabolites, certain induction strategies are used to trigger biosynthetic genes in fungi. Advancement in the computational tools helps in connecting gene clusters and their metabolite production. Therefore, modern analytical tools and the genomic era in hand leads to the identification of manifold of cryptic metabolites. The cryptic biosynthetic gene cluster (BGC) has become a treasure hunt for new metabolites representing biosynthetic pathways, regulatory mechanisms, and other factors. This review includes the use of chemical inducers/epigenetic modifiers and co-culture (species interaction) techniques to induce these BGCs. Furthermore, it cites a detailed representation of molecules isolated using these strategies. Since the induction occurs on the genomic molecular DNA and histones, this together brings a significant exploration of the biosynthetic pathways.Graphical Abstract.

Chemical Diversity of Secondary Metabolites Produced by Brazilian Endophytic Fungi

Endophytes are microorganisms that live inside vegetal tissues without causing any loss to the host plant. They display wide biosynthetic capacity when producing several bioactive secondary metabolites, whose induction could be related to activation of genes, which might be silent or expressed depending on the geographic characteristics from where the endophytic was isolated. The extraordinary richness of the Brazilian biodiversity has encouraged several research groups in the endophytic bioprospecting. This review covers natural products reported by studies on from the Brazilian endophytic fungi cultures and classified them into three chemical classes (terpenes, phenolic, and nitrogen-containing compounds). For discussion purposes, Principal Component Analysis (PCA) was used as an unsupervised explorative method to evaluate the chemical variation in the Brazilian endophyte dataset. In addition, the dendrogram from the Hierarchical Clustering Analysis (HCA) confirmed the PCA results, and HCA could identify some main endophytic clusters. Our analysis clarified how the secondary metabolites were distributed in the different Brazilian endophyte strains, and this information will be a reliable guide that will support researchers to design microbial culture strategies.

Applications of microbial co-cultures in polyketides production

Polyketides are a large group of natural biomolecules that are normally produced by bacteria, fungi and plants. These molecules have clinical importance due to their anti-cancer, anti-microbial, anti-oxidant and anti-inflammatory properties. Polyketides are biosynthesized from units of acyl-CoA by different polyketide synthases (PKSs), which display wide diversity of functional domains and mechanisms of action between fungi and bacteria. Co-culture of different micro-organisms can produce novel products distinctive from those produced during single cultures. This study compared the new polyketides produced in such co-culture systems and discusses aspects of the cultivation systems, product structures and identification techniques. Current results indicate that the formation of new polyketides may be the result of activation of previously silent PKSs genes induced during co-culture. This review indicated a potential way to produce pure therapeutic polyketides by microbial fermentation and a potential way to develop functional foods and agricultural products using co-co-culture of different micro-organisms. It also pointed out a new perspective for studies on the process of functional foods, especially those involving multiple micro-organisms.

Plant Endophytes and Epiphytes: Burgeoning Sources of Known and "Unknown" Cytotoxic and Antibiotic Agents?

In the last 20 or so years, the influence of endophytes and, quite recently, epiphytes of plants upon the compounds found in those plants, which were usually assumed to be phytochemicals produced by the plant for a variety of reasons, often as a defense against predators, is becoming more evident, in particular in the case of antitumor agents originally isolated from plant sources, though antibiotic agents might also be found, particularly from epiphytes. In this review, we started with the first report in 1993 of a taxol-producing endophyte and then expanded the compounds discussed to include camptothecin, the vinca alkaloids, podophyllotoxin, and homoharringtonine from endophytic microbes and then the realization that maytansine is not a plant secondary metabolite at all, and that even such a well-studied plant such as Arabidopsis thaliana has a vast repertoire of potential bioactive agents in its leaf epiphytic bacteria. We have taken data from a variety of sources, including a reasonable history of these discoveries that were not given in recent papers by us, nor in other papers covering this topic. The sources included the Scopus database, but we also performed other searches using bibliographic tools, thus, the majority of the papers referenced are the originals, though we note some very recent papers that have built on previous results. We concluded with a discussion of the more modern techniques that can be utilized to "persuade" endophytes and epiphytes to switch on silent biosynthetic pathways and how current analytical techniques may aid in evaluating such programs. We also comment at times on some findings, particularly in the case of homoharringtonine, where there are repetitious data reports differing by a few years claiming the same endophyte as the producer.

Antibiotic drug discovery: Challenges and perspectives in the light of emerging antibiotic resistance

Amid a rising threat of antimicrobial resistance in a global scenario, our huge investments and high-throughput technologies injected for rejuvenating the key therapeutic scaffolds to suppress these rising superbugs has been diminishing severely. This has grasped world-wide attention, with increased consideration being given to the discovery of new chemical entities. Research has now proven that the relatively tiny and simpler microbes possess enhanced capability of generating novel and diverse chemical constituents with huge therapeutic leads. The usage of these beneficial organisms could help in producing new chemical scaffolds that govern the power to suppress the spread of obnoxious superbugs. Here in this review, we have explicitly focused on several appealing strategies employed for the generation of new chemical scaffolds. Also, efforts on providing novel insights on some of the unresolved questions in the production of metabolites, metabolic profiling and also the serendipity of getting "hit molecules" have been rigorously discussed. However, we are highly aware that biosynthetic pathway of different classes of secondary metabolites and their biosynthetic route is a vast topic, thus we have avoided discussion on this topic.

Expanding the chemical diversity through microorganisms co-culture: Current status and outlook

Natural products (NPs) are considered as a cornerstone for the generation of bioactive leads in drug discovery programs. However, one of the major limitations of NP drug discovery program is "rediscovery" of known compounds, thereby hindering the rate of drug discovery efficiency. Therefore, in recent years, to overcome these limitations, a great deal of attention has been drawn towards understanding the role of microorganisms' co-culture in inducing novel chemical entities. Such induction could be related to activation of genes which might be silent or expressed at very low levels (below detection limit) in pure-strain cultures under normal laboratory conditions. In this review, chemical diversity of compounds isolated from microbial co-cultures, is discussed. For this purpose, chemodiversity has been represented as a chemical-structure network based on the "Tanimoto Structural Similarity Index". This highlights the huge structural diversity induced by microbial co-culture. In addition, the current trends in microbial co-culture research are highlighted. Finally, the current challenges (1 - induction monitoring, 2 - reproducibility, 3 - growth time effect and 4 - up-scaling for isolation purposes) are discussed. The information in this review will support researchers to design microbial co-culture strategies for future research efforts. In addition, guidelines for co-culture induction reporting are also provided to strengthen future reporting in this NP field.

Fungal Endophyte-Mediated Crop Improvement: The Way Ahead

Endophytes are non-disease causing microbes (bacteria and fungi) surviving in living tissues of plants. Their intimate association and possible coevolution with their plant partners have resulted in them contributing to an array of plant growth benefits ranging from enhanced growth and biomass accumulation, tolerance to abiotic and biotic stresses and in nutrient acquisition. The last couple of decades have witnessed a burgeoning literature on the role of endophytes (Class 3 type) in regulating plant growth and development and their adaptation to abiotic and biotic stresses. Though the underlying mechanisms of plant-endophyte interactions are far from clear, several studies have raised the hope of their potential application in agriculture, especially in mitigating abiotic and biotic stresses. The use of endophytes is envisaged as a route to reduce the production cost and burden on the environment by lessening the dependence on breeding for crop improvement and agrochemicals. Unfortunately, save a few well documented examples of their use, a little of these insights has been translated into actual agricultural applications. Here, we reflect on this paucity and elaborate on some of the important bottlenecks that might stand in way of fully realizing the potential that endophytes hold for crop improvement. We stress the need to study various facets of the endophyte-plant association for their gainful application in agriculture.

Protoilludane-type sesquiterpenoids from Armillaria sp. by co-culture with the endophytic fungus Epicoccumsp. associated with Gastrodia elata

An investigation of a co-culture of the Armillaria sp. and endophytic fungus Epicoccum sp. YUD17002 associated with Gastrodia elata led to the isolation of eight new compounds, including five protoilludane-type sesquiterpenes (1-5) and three aryl esters (6-8), together with six known analogues (9-14). The assignments of their structures were conducted via extensive analyses of the spectroscopic data and comparison of experimental and calculatedelectronic circular dichroism(ECD)data. Notably, these new compounds were not present in the pure culture controls and were only detected in the co-cultures. Compound 4 is the first example of an ent-protoilludane sesquiterpenoid scaffold bearing a five-membered lactone. Compound 6 exhibited moderate in vitro cytotoxic activities against five human cancer cell lines (HL-60, A549, MCF-7, SMMC-7721, and SW480) with IC₅₀ values ranging from 15.80 to 23.03 μM. Moreover, 6 showed weak acetylcholinesterase inhibitory activity (IC₅₀ value of 23.85 μM).

Antifungal potential of secondary metabolites involved in the interaction between citrus pathogens

Numerous postharvest diseases have been reported that cause substantial losses of citrus fruits worldwide. Penicillium digitatum is responsible for up to 90% of production losses, and represent a problem for worldwide economy. In order to control phytopathogens, chemical fungicides have been extensively used. Yet, the use of some artificial fungicides cause concerns about environmental risks and fungal resistance. Therefore, studies focusing on new approaches, such as the use of natural products, are getting attention. Co-culture strategy can be applied to discover new bioactive compounds and to understand microbial ecology. Mass Spectrometry Imaging (MSI) was used to screen for potential antifungal metabolites involved in the interaction between Penicillium digitatum and Penicillium citrinum. MSI revealed a chemical warfare between the fungi: two tetrapeptides, deoxycitrinadin A, citrinadin A, chrysogenamide A and tryptoquialanines are produced in the fungi confrontation zone. Antimicrobial assays confirmed the antifungal activity of the investigated metabolites. Also, tryptoquialanines inhibited sporulation of P. citrinum. The fungal metabolites reported here were never described as antimicrobials until this date, demonstrating that co-cultures involving phytopathogens that compete for the same host is a positive strategy to discover new antifungal agents. However, the use of these natural products on the environment, as a safer strategy, needs further investigation. This paper aimed to contribute to the protection of agriculture, considering health and ecological risks.

Microbial small molecules - weapons of plant subversion

Covering: up to 2018 Plants live in close association with a myriad of microbes that are generally harmless. However, the minority of microbes that are pathogens can severely impact crop quality and yield, thereby endangering food security. By contrast, beneficial microbes provide plants with important services, such as enhanced nutrient uptake and protection against pests and diseases. Like pathogens, beneficial microbes can modulate host immunity to efficiently colonize the nutrient-rich niches within and around the roots and aerial tissues of a plant, a phenomenon mirroring the establishment of commensal microbes in the human gut. Numerous ingenious mechanisms have been described by which pathogenic and beneficial microbes in the plant microbiome communicate with their host, including the delivery of immune-suppressive effector proteins and the production of phytohormones, toxins and other bioactive molecules. Plants signal to their associated microbes via exudation of photosynthetically fixed carbon sources, quorum-sensing mimicry molecules and selective secondary metabolites such as strigolactones and flavonoids. Molecular communication thus forms an integral part of the establishment of both beneficial and pathogenic plant-microbe relations. Here, we review the current knowledge on microbe-derived small molecules that can act as signalling compounds to stimulate plant growth and health by beneficial microbes on the one hand, but also as weapons for plant invasion by pathogens on the other. As an exemplary case, we used comparative genomics to assess the small molecule biosynthetic capabilities of the Pseudomonas genus; a genus rich in both plant pathogenic and beneficial microbes. We highlight the biosynthetic potential of individual microbial genomes and the population at large, providing evidence for the hypothesis that the distinction between detrimental and beneficial microbes is increasingly fading. Knowledge on the biosynthesis and molecular activity of microbial small molecules will aid in the development of successful biological agents boosting crop resiliency in a sustainable manner and could also provide scientific routes to pathogen inhibition or eradication.

Natural trypanocidal product produced by endophytic fungi through co-culturing

Endophytic fungi live inside vegetal tissues without causing damage to the host plant and may provide lead compounds for drug discovery. The co-culture of two or more endophytic fungi can trigger silent gene clusters, which could lead to the isolation of bioactive compounds. In this study, two endophytic strains isolated from Handroanthus impetiginosus leaves, identified as Talaromyces purpurogenus H4 and Phanerochaete sp. H2, were grown in mixed and axenic cultures. The meroterpenoid austin was detected only in the extracts from the mixed culture. Once isolated, austin displayed very interesting trypanocidal activity, with an IC₅₀ value of 36.6 ± 1.2 μg/mL against Trypanosoma cruzi in the epimastigote form. The results obtained highlight the importance of the co-culturing of endophytic fungi to obtain natural bioactive products. The findings also enhance our understanding of the ecological relationships between endophytic fungi.

Inducing Secondary Metabolite Production by Co-culture of the Endophytic Fungus Phoma sp. and the Symbiotic Fungus Armillaria sp

Co-culturing the endophytic fungus Phoma sp. YUD17001 from Gastrodia elata with Armillaria sp. in liquid nutrient medium resulted in the production of five new secondary metabolites, including two phenolic compounds, phexandiols A and B (1 and 2), three aliphatic ester derivatives, phomesters A-C (3-5), and a known fatty acid (6). The structures and absolute configurations of these compounds were elucidated by the interpretation of data from detailed spectroscopic analysis, Mosher's method, and electronic circular dichroism spectra, together with consideration of the biogenetic origins. None of the five new compounds were detected in single-strain cultures under identical fermentation conditions. The results of this work indicated that the production of 1-5 involved a complicated interaction process. None of the new compounds possessed significant cytotoxicity or antimicrobial activities.

A novel experimental system using the liverwort Marchantia polymorpha and its fungal endophytes reveals diverse and context-dependent effects

Fungal symbioses are ubiquitous in plants, but their effects have mostly been studied in seed plants. This study aimed to assess the diversity of fungal endophyte effects in a bryophyte and identify factors contributing to the variability of outcomes in these interactions. Fungal endophyte cultures and axenic liverwort clones were isolated from wild populations of the liverwort, Marchantia polymorpha. These collections were combined in a gnotobiotic system to test the effects of fungal isolates on the growth rates of hosts under laboratory conditions. Under the experimental conditions, fungi isolated from M. polymorpha ranged from aggressively pathogenic to strongly growth-promoting, but the majority of isolates caused no detectable change in host growth. Growth promotion by selected fungi depended on nutrient concentrations and was inhibited by coinoculation with multiple fungi. The M. polymorpha endophyte system expands the resources for this model liverwort. The experiments presented here demonstrate a wealth of diversity in fungal interactions even in a host reported to lack standard mycorrhizal symbiosis. In addition, they show that some known pathogens of vascular plants live in M. polymorpha and can confer benefits to this nonvascular host. This highlights the importance of studying endophyte effects across the plant tree of life.

Strategies to enhance the production of pinoresinol and its glucosides by endophytic fungus (Phomopsis sp. XP-8) isolated from Tu-chung bark

To improve the production yield of (+)-pinoresinol (Pin), (+)-pinoresinol monoglucoside (PMG), and (+)-pinoresinol diglucoside (PDG), different methods were conducted, including co-culture with resveratrol-producing Alternaria sp. MG1 spores and addition of Tu-chung in a medium at the start of cultivation, ultrasound treatment (40 kHZ, 10 min) on 5-day culture, and addition of ethanol and sodium butyrate on Day 3, followed by cultivation for an additional period of 2 days. At the end of the cultivation period (5 days), the liquid phase was collected for product analysis. Cells were collected for the determination of gene expression levels and then used in bioconversion using resting cells for another period of 2 days. The liquid phase was measured to determine the output of the target products and the expression levels of the key genes related to the biosynthesis of these compounds. Consequently, co-culture with Alternaria MG1 and addition of Tu-chung bark in the medium efficiently increased Pin, PMG, and PDG production yield in the biosynthesis systems using potato dextrose broth medium and resting cells of Phomopsis sp. XP-8. The key genes related to the biosynthesis of these compounds were significantly upregulated. However, in the majority of cases, the addition of ethanol and sodium butyrate, and ultrasound treatment decreased the production yield of Pin, PMG, and PDG. The change in production yield was not consistently accompanied by a change in gene expression.

Inducing Secondary Metabolite Production by Combined Culture of Talaromyces aculeatus and Penicillium variabile

Four new polyketides, penitalarins A-C (1-3) and nafuredin B (4), together with the known biogenetically related nafuredin A (5) were isolated from a mixed culture of a deep-sea-derived fungus Talaromyces aculeatus and a mangrove-derived fungus Penicillium variabile. Liquid chromatography/mass spectrometry analysis showed that none of compounds 1-5 was produced by either of the two fungi when cultured alone under the same condition. The structures of 1-4, including absolute configurations, were deduced based on the interpretation of MS, NMR data, and time-dependent density functional theory calculations of specific electronic circular dichroism spectra. Compounds 1-3 possess a 3,6-dioxabicyclo[3.1.0]hexane ring, and 4 showed cytotoxicity with IC₅₀ values ranging from 1.2 to 9.8 μM against a panel of human cancer cell lines.

Conditions and Regulation of Mixed Culture to Promote Shiraia bambusicola and Phoma sp. BZJ6 for Laccase Production

Mixing cultures induces the biosynthesis of laccase in mixed cells, produces signal molecules, and regulates the production of mixed-cell metabolites. The fungal strain, which promotes laccase production, has been isolated and screened from the host bamboos of endophytic fungi and identified as Phoma sp. BZJ6. When the culture medium is mainly composed of soluble starch, yeast extract, and Phoma sp., the laccase output can reach 4,680 U/L. Nitric oxide (NO) and reactive oxygen species (ROS) were found to promote the regulation of laccase synthesis. Plasma membrane NAD(P)H oxidase inhibitors and NO-specific quenchers can inhibit not only the accumulation of ROS induced and NO synthesis but also the biosynthesis of laccase. The results indicate that the accumulation of superoxide anion radical (O2-) and hydrogen peroxide (H2O2) induced by the mixed culture was partially dependent on NO. The mixed culture can also reduce the biomass, increase the synthesis of total phenolics and flavonoids, and enhance the activity of phenylalanine ammonia-lyase and chalcone isomerase. This phenomenon is probably the result of the activated phenylpropanoids-flavonoid pathway. Results confirmed that the mixture culture is advantageous for laccase production and revealed that NO, O2-, and H2O2 are necessary signal molecules to induce laccase synthesis.

Molecular inter-kingdom interactions of endophytes isolated from Lychnophora ericoides

The importance of microbial natural products has been widely demonstrated in the search for new antibiotics. However, the functional role of microbial metabolites in nature remains to be deciphered. Several natural products are known to mediate microbial interactions through metabolic exchange. One approach to investigate metabolic exchange in the laboratory is through microbial interactions. Here, we describe the chemical study of selected endophytes isolated from the Brazilian medicinal plant Lychnophora ericoides by pairwise inter-kingdom interactions in order to correlate the impact of co-cultivation to their metabolic profiles. Combining mass spectrometry tools and NMR analyses, a total of 29 compounds were identified. These compounds are members of polyene macrocycles, pyrroloindole alkaloids, angucyclines, and leupeptins chemical families. Two of the identified compounds correspond to a new fungal metabolite (29) and a new actinobacterial angucycline-derivative (23). Our results revealed a substantial arsenal of small molecules induced by microbial interactions, as we begin to unravel the complexity of microbial interactions associated with endophytic systems.

Symbiosis-inspired approaches to antibiotic discovery

Covering: 2010 up to 2017Life on Earth is characterized by a remarkable abundance of symbiotic and highly refined relationships among life forms. Defined as any kind of close, long-term association between two organisms, symbioses can be mutualistic, commensalistic or parasitic. Historically speaking, selective pressures have shaped symbioses in which one organism (typically a bacterium or fungus) generates bioactive small molecules that impact the host (and possibly other symbionts); the symbiosis is driven fundamentally by the genetic machineries available to the small molecule producer. The human microbiome is now integral to the most recent chapter in animal-microbe symbiosis studies and plant-microbe symbioses have significantly advanced our understanding of natural products biosynthesis; this also is the case for studies of fungal-microbe symbioses. However, much less is known about microbe-microbe systems involving interspecies interactions. Microbe-derived small molecules (i.e. antibiotics and quorum sensing molecules, etc.) have been shown to regulate transcription in microbes within the same environmental niche, suggesting interspecies interactions whereas, intraspecies interactions, such as those that exploit autoinducing small molecules, also modulate gene expression based on environmental cues. We, and others, contend that symbioses provide almost unlimited opportunities for the discovery of new bioactive compounds whose activities and applications have been evolutionarily optimized. Particularly intriguing is the possibility that environmental effectors can guide laboratory expression of secondary metabolites from "orphan", or silent, biosynthetic gene clusters (BGCs). Notably, many of the studies summarized here result from advances in "omics" technologies and highlight how symbioses have given rise to new anti-bacterial and antifungal natural products now being discovered.

Expanding the Chemical Repertoire of the Endophyte Streptomyces albospinus RLe7 Reveals Amphotericin B as an Inducer of a Fungal Phenotype

During an investigation of the chemistry of the endophytic actinobacterium Streptomyces albospinus RLe7, which was isolated from the roots of the Brazilian medicinal plant Lychnophora ericoides, three new natural products, (2R*,4S*)-2-((1'S*)-hydroxy-4'-methylpentyl)-4-(hydroxymethyl)butanolide (1), (3R*,4S*,5R*,6S*)-tetrahydro-4-hydroxy-3,5,6-trimethyl-2-pyranone (2), and 1-O-(phenylacetyl)glycerol (3), together with known secondary metabolites (S)-4-benzyl-3-oxo-3,4-dihydro-1H-pyrrolo[2,1-c][1,4]oxazine-6-carbaldehyde (4), (S)-4-isobutyl-3-oxo-3,4-dihydro-1H-pyrrolo[2,1-c][1,4]oxazine-6-carbaldehyde (5), and the diketopiperazines cyclo(l-Tyr-l-Pro) (6) and cyclo(l-Val-l-Pro) (7), were isolated. The role of isolated natural products in the interaction between S. albospinus RLe7 and the fungus Coniochaeta sp. FLe4, an endophyte from the same plant, was investigated. None of these isolated actinobacterial compounds were able to inhibit the fungus or induce the fungal red pigmentation observed when both endophytes interact. Further investigation using mass spectrometry approaches enabled identifying the well-known antifungal compound amphotericin B (9) as a microbial metabolite of S. albospinus RLe7. Finally, compound 9 was demonstrated as at least one of the agents responsible for both the antifungal activity and induction of red-pigmented fungal phenotype.

Predominately Uncultured Microbes as Sources of Bioactive Agents

In this short review, I am discussing the relatively recent awareness of the role of symbionts in plant, marine-invertebrates and fungal areas. It is now quite obvious that in marine-invertebrates, a majority of compounds found are from either as yet unculturable or poorly culturable microbes, and techniques involving “state of the art” genomic analyses and subsequent computerized analyses are required to investigate these interactions. In the plant kingdom evidence is amassing that endophytes (mainly fungal in nature) are heavily involved in secondary metabolite production and that mimicking the microbial interactions of fermentable microbes leads to involvement of previously unrecognized gene clusters (cryptic clusters is one name used), that when activated, produce previously unknown bioactive molecules.

Camptothecine production by mixed fermentation of two endophytic fungi from Nothapodytes nimmoniana

Two endophytic fungi isolated from the endangered plant Nothapodytes nimmoniana (Grah.) Mabb. were found to effectively synthesize CPT independent of their host plant under submerged fermentation conditions. Molecular characterization of fungi revealed their identity as Colletotrichum fructicola SUK1 (F1) and Corynespora cassiicola SUK2 (F2). Mixed fermentation experiments were carried out to study the effect of microbial signalling between the two fungal species on camptothecine production. Effect of culture parameters on CPT production was studied for both mono-cultures (F1 and F2) separately as well as for the mixed fermentation (F1 + F2). Further the most influencing ones were optimized statistically using response surface methodology. Statistical model based optimized parameters were whey (70 %), agitation rate (110 rpm), temperature (30 °C), and incubation period (7 d) for the mixed fermentation. Monocultures of the two fungal species F1 and F2 yielded CPT up to 33 ± 1.1 mg l(-1)and 69 ± 1.1 mg l(-1), respectively; while their mixed fermentation under the optimized conditions yielded up to 146 ± 0.2 mg l(-1). HPLC and LC-MS/MS techniques were used to analyze the products obtained.

Endophytes as in vitro production platforms of high value plant secondary metabolites

Many reports have been published on bioprospecting of endophytic fungi capable of producing high value bioactive molecules like, paclitaxel, vincristine, vinblastine, camptothecin and podophyllotoxin. However, commercial exploitation of endophytes for high value-low volume plant secondary metabolites remains elusive due to widely reported genomic instability of endophytes in the axenic culture. While most of the endophyte research focuses on screening endophytes for novel or existing high value biomolecules, very few reports seek to explore the possible mechanisms of production of host-plant associated or novel secondary metabolites in these organisms. With an overview of host-endophyte relationship and its possible impact on the secondary metabolite production potential of endophytes, the review highlights the evidence reported for and against the presence of host-independent biosynthetic machinery in endophytes. The review aims to address the question, why should and how can endophytes be exploited for large scale in vitro production of high value phytochemicals? In this regard, various bioprocess optimization strategies that have been applied to sustain and enhance the product yield from the endophytes have also been described in detail. Further, techniques like mixed fermentation/co-cultivation and use of epigenetic modifiers have also been discussed as potential strategies to activate cryptic gene clusters in endophytes, thereby aiding in novel metabolite discovery and overcoming the limitations associated with axenic culture of endophytes.