Bioactive Compounds from Endophytes and their Potential in Pharmaceutical Effect: A Review

Molecular authentication, metabolite profiling and in silico-in vitro cytotoxicity screening of endophytic Penicillium ramusculum from Withania somnifera for breast cancer therapeutics

In the present study, we isolated a potent endophytic fungus from the roots of Withania somnifera. The endophytic fungal strain was authenticated as Penicillium ramusculum SVWS3 based on morphological and molecular sequencing using four gene data and phylogenetic analyses. In vitro cytotoxicity studies unveiled the remarkable cytotoxic potential of the crude extract derived from P. ramusculum, exhibiting dose-dependent effects on MDA-MB-468 and MCF-7 cells. At a concentration of 100 µg/mL, the crude extract resulted in cell viability of 29.78% for MDA-MB-468 cells and 14.61% for MCF-7 cells. The IC50 values were calculated as 62.83 ± 0.93 µg/mL and 17.23 ± 1.43 µg/mL, respectively for MDA-MB-468 and MCF-7 cells. Caspase activation assay established the underlying mechanism of the crude extract depicting the activation of caspases 3 and 7, indicating the induction of apoptosis in MCF-7 cells. Chemotaxonomic profiling elucidated the ability of P. ramusculum to synthesize a diverse array of bioactive compounds, including Fasoracetam, Tryprostatin B, Odorinol, Thyronine, Brevianamide F, Proglumide, Perlolyrine, Tyrphostin B48, Baptifoline, etc. Molecular docking studies inferred that Baptifoline, Brevianamide F, Odorinol, Perlolyrine, Thyronine, Tryphostin B48, and Tryprostatin B were the lead compounds that could effectively interact with the five selected target receptors of breast cancer, further surpassing the positive controls analyzed. Pharmacokinetic profiling revealed that Baptifoline, Odorinol, and Thyronine depicted an excellent therapeutic profile of druggability. These findings collectively substantiate the anticancer activity of bioactive metabolites synthesized by P. ramusculum SVWS3. Hence, the endophytic P. ramusculum SVWS3 can be an authentic source for developing novel chemotherapeutic drug formulations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03906-3.

Molecular Identification of Fungal Endophytes of Medicinal Plant Citrullus colocynthis (L.) Schrad as a Medicinal Plant: Role of Tissue Type and Sampling Location on the Diversity

Endophytic fungi are an important group of organisms in association with plants which are able to colonize all plant internal tissues and improve their fitness. The present research aims to isolate and identify endophytic fungi of Citrullus colocynthis plant and then investigate the effects of sampling location and tissue type on the fungal endophyte diversity of this plant. To do so, a sampling program was done in 11 geographically isolated C. colocynthis growing areas of Hormozgan province, Iran. For molecular identification of endophytic fungi of C. colocynthis, the internal transcribed spacer region (ITS1-5.8S-ITS4), as a universal DNA barcode marker for fungi, was amplified using primer sets. Totally, 12 taxa (Alternaria solani, Cladosporium halotolerans, Setosphaeria rostrata, Aspergillus niger, A. allahabadii, A. terreus, A. occultus, A. cristatus, Penicillium chrysogenum, Talaromyces purpureogenus, Fusarium sp., and Pseudozyma flocculosa) were isolated. Our findings also showed that the diversity of fungal endophytes isolated from C. colocynthis was affected by the tissue type and sampling site. Accordingly, the leaves and seeds were found to have the highest and lowest rates of endophyte colonization and richness in all sampling seasons, respectively. Simpson's diversity index of 0.8165 in root tissue indicated the high diversity of endophytes in this organ. In addition, Shannon's diversity index in the root (1.846) was higher than that in the other organs. The highest Shannon's and Simpson's indices were observed in Khoon Sorkh and Minab regions. Generally, at least two factors (region and type of tissue) played the most important roles in determining the composition of fungal endophytes in C. colocynthis.

Endophytic fungi as a potential source of anti-cancer drug

Endophytes are considered one of the major sources of bioactive compounds used in different aspects of health care including cancer treatment. When colonized, they either synthesize these bioactive compounds as a part of their secondary metabolite production or augment the host plant machinery in synthesising such bioactive compounds. Hence, the study of endophytes has drawn the attention of the scientific community in the last few decades. Among the endophytes, endophytic fungi constitute a major portion of endophytic microbiota. This review deals with a plethora of anti-cancer compounds derived from endophytic fungi, highlighting alkaloids, lignans, terpenes, polyketides, polyphenols, quinones, xanthenes, tetralones, peptides, and spirobisnaphthalenes. Further, this review emphasizes modern methodologies, particularly omics-based techniques, asymmetric dihydroxylation, and biotic elicitors, showcasing the dynamic and evolving landscape of research in this field and describing the potential of endophytic fungi as a source of anticancer drugs in the future.

Screening of Anti-Inflammatory Activity and Metabolomics Analysis of Endophytic Fungal Extracts; Identification and Characterization of Perylenequinones and Terpenoids from the Interesting Active Alternaria Endophyte

Patients suffering from inflammatory chronic diseases are classically treated with anti-inflammatory drugs but unfortunately are highly susceptible to becoming resistant to their treatment. Finding new drugs is therefore crucial and urgent and research on endophytic fungi is a promising way forward. Endophytic fungi are microorganisms that colonize healthy plants and live within their intercellular tissues. They are able to produce a large variety of secondary metabolites while allowing their host to stay healthy. A number of these molecules are endowed with antioxidant or antimicrobial as well as cytotoxic properties, making them very interesting/promising in the field of human therapy. The aim of our study was to investigate whether extracts from five endophytic fungi isolated from plants are endowed with anti-inflammatory activity. Extracts of the endophytic fungi Alternaria alternata from Calotropis procera leaves and Aspergillus terreus from Trigonella foenum-graecum seeds were able to counteract the lipopolysaccharide (LPS) pro-inflammatory effect on THP-1 cells differentiated into macrophages. Moreover, they were able to induce an anti-inflammatory state, rendering them less sensitive to the LPS pro-inflammatory stimulus. Taken together, these results show that these both endophytic fungi could be interesting alternatives to conventional anti-inflammatory drugs. To gain more detailed knowledge of their chemical richness, phytochemical analysis of the ethyl acetate extracts of the five endophytic fungi studied was performed using HPTLC, GC-MS and LC-MS with the Global Natural Products Social (GNPS) platform and the MolNetEnhancer tool. A large family of metabolites (carboxylic acids and derivatives, steroid derivatives, alkaloids, hydroxyanthraquinones, valerolactones and perylenequinones) were detected. The purification of endophytic fungus extract of Alternaria alternate, which diminished TNF-α production of 66% at 20 µg/mL, incubated one hour before LPS addition, led to the characterization of eight pure compounds. These molecules are altertoxins I, II, III, tricycloalternarenes 3a, 1b, 2b, anthranilic acid, and o-acetamidobenzoic acid. In the future, all these pure compounds will be evaluated for their anti-inflammatory activity, while altertoxin II has been shown in the literature as the most active mycotoxin in terms of anti-inflammatory activity.

Seeds of Stevia rebaudiana Bertoni as a Source of Plant Growth-Promoting Endophytic Bacteria with the Potential to Synthesize Rebaudioside A

In this study, a new strain of Pantoea vagans, SRS89, was isolated from surface-sterilized stevia seeds. The isolate was evaluated using morphological, molecular, and biochemical methods. The bacterium was 1.5 μm long, yellowish in color, and classified as Gram-negative. Whole genome sequencing of our strain revealed the presence of a 4,610,019 bp chromosome, and genome annotation resulted in the detection of 4283 genes encoding 4204 putative coding sequences. Phylogenic analysis classified the genome of our strain close to the MP7 and LMG 24199 strains of P. vagans. Functional analysis showed that the highest number of genes within the analyzed bacterium genome were involved in transcription, amino acid transport and metabolism, and carbohydrate transport and metabolism. We also identified genes for enzymes involved in the biosynthesis of carotenoids and terpenoids. Furthermore, we showed the presence of growth regulators, with the highest amount noted for gibberellic acid A₃, indole-3-acetic acid, and benzoic acid. However, the most promising property of this strain is its ability to synthesize rebaudioside A; the estimated amount quantified using reversed-phase (RP)-HPLC was 4.39 mg/g of the dry weight of the bacteria culture. The isolated endophytic bacterium may be an interesting new approach to the production of this valuable metabolite.

The Multifunctions and Future Prospects of Endophytes and Their Metabolites in Plant Disease Management

Endophytes represent a ubiquitous and magical world in plants. Almost all plant species studied by different researchers have been found to harbor one or more endophytes, which protect host plants from pathogen invasion and from adverse environmental conditions. They produce various metabolites that can directly inhibit the growth of pathogens and even promote the growth and development of the host plants. In this review, we focus on the biological control of plant diseases, aiming to elucidate the contribution and key roles of endophytes and their metabolites in this field with the latest research information. Metabolites synthesized by endophytes are part of plant disease management, and the application of endophyte metabolites to induce plant resistance is very promising. Furthermore, multi-omics should be more fully utilized in plant–microbe research, especially in mining novel bioactive metabolites. We believe that the utilization of endophytes and their metabolites for plant disease management is a meaningful and promising research direction that can lead to new breakthroughs in the development of more effective and ecosystem-friendly insecticides and fungicides in modern agriculture.

Bioinformatic comparison of three Embleya species and description of steffimycins production by Embleya sp. NF3

The Embleya genus is a new member of the Streptomycetaceae family formed by only two species isolated from soil (Embleya scabrispora and Embleya hyalina). Strain NF3 is an endophytic actinobacterium obtained from the medicinal tree Amphipterygium adstringens. By 16S rRNA gene analysis, NF3 strain was identified as Embleya sp., closely related to E. hyalina. In our interest to deep into the NF3 strain features, a bioinformatic study was performed on the Embleya genus based on their genome information to produce secondary metabolites. A comparative analysis of the biosynthetic gene clusters (BGCs) of NF3 with the two released Embleya genomes revealed that NF3 has 49 BGCs, E. scabrispora DSM41855 has 50 BGCs, and E. hyalina NBRC13850 has 46 BGCs. Although bearing similar cluster numbers, the three strains shared only 25% of the BGCs information. NF3 encoded the nybomycin cluster detected in E. hyalina NBRC13850 and lacked the hitachimycin cluster present in E. scabrispora DSM41855. On the contrary, strain NF3 contained a cluster for the anthracycline steffimycin, neither encoded by E. hyalina NBRC13850 nor by E. scabrispora DSM41855. Our results and previous characterization studies supported strain NF3 as a new member of the genus Embleya. The chemical analysis of the steffimycins produced by strain NF3 showed the production of eight compounds of the steffimycins and steffimycinone families. Four of these molecules have already been described: steffimycin B, steffimycin C, 8-demethoxy-10-deoxysteffimycinone, and 7-deoxiesteffimycinone, and four are new natural products: 8-demethoxysteffimycin B, 8-demethoxy-10-deoxysteffimycin B, 7-deoxy-8-demethoxysteffimycinone, and 7-deoxy-10-deoxysteffimycinone. With this information, we proposed an alternative pathway to produce StefB. Among steffimycins, StefB was the main compound produced by this strain (29.8%) and showed the best cytotoxic activity. KEY POINTS: • The Embleya genus and its biosynthetic potential • An alternative biosynthetic pathway for steffimycins biosynthesis • Four new natural products of the steffimycin family.

Comoclathrin, a novel potent skin-whitening agent produced by endophytic Comoclathris strains associated with Andalusia desert plants

As part of our screening program for the discovery of molecules of microbial origin with skin-whitening activity, 142 diverse fungal endophytes from a wide variety of Andalusia arid plants were screened, applying the OSMAC approach. The fungal strains CF-090361 and CF-090766, isolated from xerophytic plants, were selected as the most promising, while phylogenetic analysis revealed that both strains could represent a new species within the genus Comoclathris. The effect of different fermentation conditions on the production of tyrosinase inhibitory activity was examined, in order to identify the optimum cultivation conditions. LCMS based metabolomics was applied to determine significant differences between the strains and fermentation conditions, and to identify potential bioactive secondary metabolites. Bioassay-guided purification of the main active components led to the isolation of three new compounds (1–3), along with the known compounds graphostrin B (4) and brevianamide M (5). Compound 1 (Comoclathrin) demonstrated the strongest anti-tyrosinase activity (IC₅₀ 0.16 μΜ), which was 90-times higher than kojic acid (IC₅₀ 14.07 μΜ) used as positive control. Additionally, comoclathrin showed no significant cytotoxicity against a panel of cancer cell lines (HepG2, A2058, A549, MCF-7 and MIA PaCa-2) and normal BJ fibroblasts. These properties render comoclathrin an excellent development candidate as whitening agent.

Fungal Endophytes and Their Role in Agricultural Plant Protection against Pests and Pathogens

Virtually all examined plant species harbour fungal endophytes which asymptomatically infect or colonize living plant tissues, including leaves, branches, stems and roots. Endophyte-host interactions are complex and span the mutualist-pathogen continuum. Notably, mutualist endophytes can confer increased fitness to their host plants compared with uncolonized plants, which has attracted interest in their potential application in integrated plant health management strategies. In this review, we report on the many benefits that fungal endophytes provide to agricultural plants against common non-insect pests such as fungi, bacteria, nematodes, viruses, and mites. We report endophytic modes of action against the aforementioned pests and describe why this broad group of fungi is vitally important to current and future agricultural practices. We also list an extensive number of plant-friendly endophytes and detail where they are most commonly found or applied in different studies. This review acts as a general resource for understanding endophytes as they relate to potential large-scale agricultural applications.

Therapeutic prospects of endophytic Bacillus species from Berberis lycium against oxidative stress and microbial pathogens

Endophytes are microorganisms residing within plant tissues. Bacterial endophytes are important sources for production of pharmaceutically important metabolites. Berberis lycium is an important medicinal plant and there exist no report regarding isolation and determination of bioactive potential of its bacterial endophytes. Therefore the present study was aimed to isolate and identify bacterial endophytes from Berberis lycium. The study resulted in isolation of 20 strains of bacterial endophytes. Based on their antibacterial activity three strains were identified as Bacillus cereus (LBL6), Bacillus thuringiensis (SBL3) and Bacillus anthracis (SBL4) on basis of 16SrRNA gene using universal primers. Crude ethyl acetate extracts of LBL6, SBL3 and SBL4 were further evaluated for antioxidant and antifungal activities. Moderate antioxidant activity (56 %) at a concentration of 1000 µg/mL was observed for LBL6 followed by 45 and 43 % activity by SBL4 and SBL3 respectively. Significant antifungal activity was observed against Aspergillus niger (60 %) and Aspergillus flavus (56 %) at concentration of 4 mg/mL of SBL3 and SBL4 respectively. GCMS analysis of extract (LBL6) exhibited presence of 12 bioactive secondary metabolites corresponding to antimicrobial, antifungal, antioxidant, antitumor and anticancer activities. In conclusion, present study highlighted the importance of Berberis lycium to host diverse bacterial endophytes of pharmaceutical importance.

General Limitations to Endophytic Entomopathogenic Fungi Use as Plant Growth Promoters, Pests and Pathogens Biocontrol Agents

The multiple roles of fungal entomopathogens in host plants' growth promotion, pest and pathogen management have drawn huge attention for investigation. Endophytic species are known to influence various activities of their associated host plants, and the endophyte-colonized plants have been demonstrated to gain huge benefits from these symbiotic associations. The potential application of fungal endophytes as alternative to inorganic fertilizers for crop improvement has often been proposed. Similarly, various strains of insect pathogenic fungi have been formulated for use as mycopesticides and have been suggested as long-term replacement for the synthetic pesticides that are commonly in use. The numerous concerns about the negative effects of synthetic chemical pesticides have also driven attention towards developing eco-friendly pest management techniques. However, several factors have been underlined to be militating the successful adoption of entomopathogenic fungi and fungal endophytes as plant promoting, pests and diseases control bio-agents. The difficulties in isolation and characterization of novel strains, negative effects of geographical location, vegetation type and human disturbance on fungal entomopathogens, are among the numerous setbacks that have been documented. Although, the latest advances in biotechnology and microbial studies have provided means of overcoming many of these problems. For instance, studies have suggested measures for mitigating the negative effects of biotic and abiotic stressors on entomopathogenic fungi in inundative application on the field, or when applied in the form of fungal endophytes. In spite of these efforts, more studies are needed to be done to achieve the goal of improving the overall effectiveness and increase in the level of acceptance of entomopathogenic fungi and their products as an integral part of the integrated pest management programs, as well as potential adoption as an alternative to inorganic fertilizers and pesticides.

A plant endophyte Staphylococcus hominis strain MBL_AB63 produces a novel lantibiotic, homicorcin and a position one variant

Here we report a jute endophyte Staphylococcus hominis strain MBL_AB63 isolated from jute seeds which showed promising antimicrobial activity against Staphylococcus aureus SG511 when screening for antimicrobial substances. The whole genome sequence of this strain, annotated using BAGEL4 and antiSMASH 5.0 to predict the gene clusters for antimicrobial substances identified a novel antimicrobial peptide cluster that belongs to the class I lantibiotic group. The predicted lantibiotic (homicorcin) was found to be 82% similar to a reported peptide epicidin 280 having a difference of seven amino acids at several positions of the core peptide. Two distinct peaks obtained at close retention times from a RP-HPLC purified fraction have comparable antimicrobial activities and LC-MS revealed the molecular mass of these peaks to be 3046.5 and 3043.2 Da. The presence of an oxidoreductase (homO) similar to that of epicidin 280- associated eciO or epilancin 15X- associated elxO in the homicorcin gene cluster is predicted to be responsible for the reduction of the first dehydrated residue dehydroalanine (Dha) to 2-hydroxypropionate that causes an increase of 3 Da mass of homicorcin 1. Trypsin digestion of the core peptide and its variant followed by ESI-MS analysis suggests the presence of three ring structures, one in the N-terminal and other two interlocking rings at the C-terminal region that remain undigested. Homicorcin exerts bactericidal activity against susceptible cells by disrupting the integrity of the cytoplasmic membrane through pore formation as observed under FE-SEM.

Endophytic Microbial Diversity: A New Hope for the Production of Novel Anti-tumor and Anti-HIV Agents as Future Therapeutics

Cancer is a collective name for a variety of diseases that can begin in virtually every organ or body tissue as abnormal cells develop uncontrollably and ten million new cancer cases are diagnosed all over the world at present. Whereas HIV is a virus that makes people susceptible to infection and contributes to the condition of acquired immune deficiency syndrome (AIDS). Almost 37 million people are currently diagnosed with HIV and 1 million people die every year, which is the worst-case scenario. Potential medicinal compounds have played a crucial role in the production of certain clinically beneficial novel anti-cancer and anti-HIV agents that are produced from natural sources especially from plants. These include Taxol, Vinblastine, Podophyllotoxin, Betulinic acid, Camptothecin, and Vincristine, etc. In the past decades, bioactive compounds were extracted directly from the plant sources which was more time consuming, led to low yield productivity, high cost, and bad impact on biodiversity. Endophytes, the microorganisms that reside inside the host plant by not causing any kind of harm to them and have potential applications in agriculture, medicine, pollution, and food industries. Therefore, by isolating and characterizing novel endophytes from medicinal plants and extracting their secondary metabolites to produce useful bioactive compounds can be beneficial for well-being and society as a future therapeutics. This approach is not harmful to biodiversity economical, timesaving, low cost, and can lead to the discovery of various industrial and commercially important novel anti-tumor and anti-HIV agents in the future. The Himalayas are home to several medicinal plants and the endophytic microbial biodiversity of the Himalayan region is also not much explored yet. However, the effect of compounds from these endophytes on anticancer and antiviral activity, especially anti-HIV has been largely unexplored. Hence, the present review is designed to the exploration of endophytic microbial diversity that can give rise to the discovery of various novel potential industrially valuable bioactive compounds that can lessen the rate of such type of pandemic diseases in the future by providing low-cost future therapeutics in future.

Applications of endophytic microbes in agriculture, biotechnology, medicine, and beyond

Endophytes are emerging as integral components of plant microbiomes. Some of them play pivotal roles in plant development and plant responses to pathogens and abiotic stresses, whereas others produce useful and/or interesting secondary metabolites. The appreciation of their abilities to affect plant phenotypes and produce useful compounds via genetic and molecular interactions has paved the way for these abilities to be exploited for health and welfare of plants, humans and ecosystems. Here we comprehensively review current and potential applications of endophytes in the agricultural, pharmaceutical, and industrial sectors. In addition, we briefly discuss the research objectives that should be focused upon in the coming years in order for endophytes and their metabolites to be fully harnessed for potential use in diverse areas.

Endophytic microbes from Nigerian ethnomedicinal plants: a potential source for bioactive secondary metabolites-a review

BACKGROUND

Endophytes are highly beneficial species of microbes that live in symbiosis with plant tissues in the setting. Endophytes are difficult to isolate in their natural environment, and they are understudied despite being a rich source of bioactive molecules. There are varieties of new infectious diseases emerging across the world, necessitating a constant and expanded search for newer and more efficient bioactive molecules. Nigeria is known for its biodiversity in ethnomedicinal plants, yet these plants are understudied for endophytic microbes harbouring novel bioactive molecules.

MAIN BODY

Endophytes are a source of novel organic natural molecules and are thought to be drug discovery frontiers. Endophyte research has contributed to the discovery of possible anticancer agents following the discovery of taxol. Endophyte research has contributed to the discovery of possible drug compounds with antimicrobial, antioxidant, antiviral, antidiabetic, anti-Alzheimers disease and immunosuppressive properties among others. These breakthroughs provide hope for combating incurable diseases, drug resistance, the emergence of new infectious diseases, and other human health issues. Finding new medicines that may be effective candidates for treating newly emerging diseases in humans has a lot of promise. Most studies have been on fungi endophytes, with just a few reports on bacterial endophytes. The biology of endophytic bacteria and fungi, as well as endophytic microbes isolated from Nigerian medicinal plants, their isolation methods, identification by morphological and molecular methods, fermentation, purification, identification of bioactive compounds and biosynthetic gene clusters are all covered in this study.

CONCLUSION

In Nigeria, the sourcing and isolation of endophytes harboring biosynthetic gene clusters are still understudied, necessitating a rigorous quest for bioactive molecules in endophytes inhabiting various ethnomedicinal plants.

Fungal endophytes from leaves of Avicennia marina growing in semi-arid environment as a promising source for bioactive compounds

Endophytic fungi are broadly dispersed residing inside plant tissues and have been demonstrated as a treasure for bioactive natural products. Unexplored harsh and heavy metal contaminant habitat of Avicennia marina may have diverse and potential fungal association. Therefore, this work aimed to isolate the culturable fungal endophytes associated with leaves of A. marina and to evaluate their medical potentialities. Seventeen isolates of endophyte fungi were isolated from healthy leaves and their antimicrobial activities were evaluated. Results showed that isolates had activity against micro-organisms in addition to their antioxidant activity produced a variety of phenolic compounds, besides exhibited a lowest cytotoxicity against ATCC-CCL-81 cell line. Consequently, selected endophytic fungal isolates were identified genetically as Chaetomium sp., Chaetomium madrasense, Chaetomium sp., Chaetomium globosum, Aspergillus hiratsukae, Aspergillus ochraceus, Alternaria tenuissima and Curvularia lunata with gene bank accession numbers MT089951, MT089952, MT089953, MT089954, MT089955, MT089956, MT089957 and MT089958 respectively. The most potent fungus extract was analysed using Gas chromatography-mass spectrometry which verified the presence of numerous bioactive compounds. These findings confirmed that new endophytic fungal strains derived from A. marina thrive in harsh ecosystem produce bioactive metabolites which can be recommended as a novel source for drug discovery.

Exploring the potentialities of beneficial endophytes for improved plant growth

Pathogen affects plant growth, host health and productivity. Endophytes, presumed to live inside the plant tissues, might be helpful in sustaining the future of agriculture. Although recent studies have proven that endophytes can be pathogenic, commensal, non-pathogenic, and/or beneficial, this review will focus on the beneficial category only. Beneficial endophytes produce a number of compounds which are useful for protecting plants from environmental conditions, enhancing plant growth and sustainability, while living conveniently inside the hosts. The population of endophytes is majorly controlled by location, and climatic conditions where the host plant grows. Often the most frequently isolated endophytes from the tissues of the plant are fungi, but sometimes greater numbers of bacteria are isolated. Beneficial endophytes stand a chance to replace the synthetic chemicals currently being used for plant growth promotion if carefully explored by researchers and embraced by policymakers. However, the roles of endophytes in plant growth improvement and their behavior in the host plant have not been fully understood. This review presents the current development of research into beneficial endophytes and their effect in improving plant growth.

Elucidating Mechanisms of Endophytes Used in Plant Protection and Other Bioactivities With Multifunctional Prospects

Endophytes are abundant in plants and studies are continuously emanating on their ability to protect plants from pathogens that cause diseases especially in the field of agriculture. The advantage that endophytes have over other biocontrol agents is the ability to colonize plant's internal tissues. Despite this attributes, a deep understanding of the mechanism employed by endophytes in protecting the plant from diseases is still required for both effectiveness and commercialization. Also, there are increasing cases of antibiotics resistance among most causative agents of diseases in human beings, which calls for an alternative drug discovery using natural sources. Endophytes present themselves as a storehouse of many bioactive metabolites such as phenolic acids, alkaloids, quinones, steroids, saponins, tannins, and terpenoids which makes them a promising candidate for anticancer, antimalarial, antituberculosis, antiviral, antidiabetic, anti-inflammatory, antiarthritis, and immunosuppressive properties among many others, even though the primary function of bioactive compounds from endophytes is to make the host plants resistant to both abiotic and biotic stresses. Endophytes still present themselves as a peculiar source of possible drugs. This study elucidates the mechanisms employed by endophytes in protecting the plant from diseases and different bioactivities of importance to humans with a focus on endophytic bacteria and fungi.

Antimicrobial Exploration Between Counterpart Endosymbiont and Host Plant (Tamarindus indica Linn.)

Background::

Endophytic bacteria produce various bioactive secondary metabolites, which benefit human health. Tamarindus indica L. is well known for its medicinal value in human health care. Several studies have reported on its biological effects from various parts of T. indica, but only a few studies have been devoted to examining the biological activity of endophytes of T. indica.

Objectives:

In the present study, an endophyte was isolated from the leaves of T. indica and screened for its antimicrobial potential.

Methods:

The selected endophyte was identified by 16s rRNA partial genome sequencing and investigated for their antimicrobial potency. The preliminary phytochemical tests were conducted for the affirmation of phytoconstituents in the endophytic crude ethyl acetate extract of T. indica (TIM) and total phenolic content was performed. The antimicrobial potential of TIM was evaluated against human pathogenic ATCC gram-positive and gram-negative bacterial strains.

Results:

TIM exhibited an appreciable amount of gallic acid equivalent phenolic content (21.6 ± 0.04 mg GAE/g of crude extract). TIM showed the Minimum Inhibitory Concentration (MIC) at 250 μg/mL and Minimum Bactericidal Concentration (MBC) at 500 μg/mL among the selected human pathogenic ATCC strains. At MIC of 500 μg/mL, TIM displayed a significant zone of inhibition against P. aeruginosa and N. gonorrhoeae.

Conclusion:

The results from our study highlighted for the first time the antimicrobial potential of endophytic bacterial strain Bacillus velezensis in T. indica leaves and it could be further explored as a source of natural antimicrobial agents.

Novel [6]-gingerol Triazole Derivatives and their Antiproliferative Potential against Tumor Cells

BACKGROUND

Effective cancer treatment is a major public health challenge. The limitations of current therapies and their adverse effects reduce the efficacy of treatment, leading to significant mortality rates worldwide. Moreover, natural product chemistry occupies a prominent role in the search for new treatment alternatives, by contributing a spectrum of chemical structures that may potentially yield new bioactive compounds. The compound [6]-gingerol (1) is the main active substance in ginger (Zingiber officinale) and several studies have shown it to produce beneficial effects, including antitumor activity.

OBJECTIVE

This work aims to obtain new gingerol derivatives with cytotoxic activity.

METHODS

[6]-gingerol was isolated and its derivatives were produced using click chemistry, obtaining eight new compounds. All chemical structures were determined by means of IR, NMR and HRMS data, and cytotoxicity was evaluated in the HCT 116 (colon carcinoma) and MCF-7 (breast carcinoma) cell lines at concentrations of 5 µmol L-1 and 50 µmol L-1.

RESULTS

At 50 µmol L-1, more than 70% inhibition of cell growth was achieved with compounds 2e, 2g against HCT 116, and 2b, 2d, 2e, 2f and 2g against MCF-7.

CONCLUSION

The obtained compounds showed only moderate cytotoxic activity. However, the products with substituents occupying the meta position in relation to the triazole ring showed increased cytotoxic properties. The brominated compound (2g) showed the strongest activity, inhibiting cell proliferation by 87%.

Phyllospheric Microbiomes: Diversity, Ecological Significance, and Biotechnological Applications

The phyllosphere referred to the total aerial plant surfaces (above-ground portions), as habitat for microorganisms. Microorganisms establish compositionally complex communities on the leaf surface. The microbiome of phyllosphere is rich in diversity of bacteria, fungi, actinomycetes, cyanobacteria, and viruses. The diversity, dispersal, and community development on the leaf surface are based on the physiochemistry, environment, and also the immunity of the host plant. A colonization process is an important event where both the microbe and the host plant have been benefited. Microbes commonly established either epiphytic or endophytic mode of life cycle on phyllosphere environment, which helps the host plant and functional communication with the surrounding environment. To the scientific advancement, several molecular techniques like metagenomics and metaproteomics have been used to study and understand the physiology and functional relationship of microbes to the host and its environment. Based on the available information, this chapter describes the basic understanding of microbiome in leaf structure and physiology, microbial interactions, especially bacteria, fungi, and actinomycetes, and their adaptation in the phyllosphere environment. Further, the detailed information related to the importance of the microbiome in phyllosphere to the host plant and their environment has been analyzed. Besides, biopotentials of the phyllosphere microbiome have been reviewed.

Anti-leishmanial and Anti-inflammatory Agents from Endophytes: A Review

Leishmaniases and chronic inflammatory diseases are the cause of millions of deaths in the world each year. The treatment of leishmaniasis is facing serious drawbacks particularly due to the limited number of effective medicines, the resistance, and the toxicity of available drugs. On the other hand, many drugs are used for the management of inflammatory disorders. However, the most commonly prescribed although efficient is highly toxic with multiples side effects. New leads compounds for the development of new anti-leishmanial and anti-inflammatory drugs are needed. Over the past decade, several studies on the potential of endophytes to produce bioactive metabolites have been reported. We are presenting in the present review the status of research from 2000 to 2019 on the anti-leishmanial and anti-inflammatory metabolites isolated from endophytes from diverse habitats. An emphasis was put on existing gaps in the literature to inspire and guide future investigations. We hope that this review will help accelerate the drug discovery against leishmaniases and inflammation-associated disorders.

Antiplasmodial potential and GC-MS fingerprint of endophytic fungal extracts derived from Cameroonian Annona muricata

ETHNOPHARMACOLOGICAL RELEVANCE

Annona muricata (Annonaceae) is a commonly used medicinal plants in Cameroonian traditional medicines to treat various diseases including malaria. Previous studies have shown that extracts from this plant have antiplasmodial activity.

AIM OF THE STUDY

This study aimed to explore the endophyic fungi associated with some parts of this plant for their ability to produce antiplasmodial metabolites.

MATERIALS AND METHODS

One hundred and fifty-two endophytic fungi isolated from twelve different organs of A. muricata were cultured and the ethyl acetate extracts of conditioned media screened for antiplasmodial activity using the 96-well microtiter plate format SYBR green florescence assay against Chloroquine-sensitive Pf3D7 and Chloroquine-resistant PfINDO/PfDd2 strains of Plasmodium falciparum.

RESULTS

Twenty-seven (17.76%) of fungi tested were found to completely inhibit the growth of Plasmodium parasites at 10 µg/mL. The 5.8S rDNA sequencing data revealed the strongly active (IC₅₀ < 2 µg/mL against at least 2 P. falciparum strains) isolates to be Trichoderma afroharzianum AMrb7, Penicillium citrinum AMrb11, Neocosmospora rubicola AMb22, Penicillium tropicum AMb3, Penicillium citrinum AMrb23, Aspergillus versicolor AMb7, and Fusarium sp AMst1. Of these, the extracts from Penicillium citrinum AMrb11 (IC₅₀ 0.84-0.93 μg/mL) and Neocosmospora rubicola AMb22 (IC₅₀ 0.39-1.92 μg/mL) showed the highest promise against all three plasmodial strains with selectivity indices ranging from 34.71 to 180.97. Dynamic head space GC-MS analysis of ethyl acetate extracts of promising fungi revealed broad-spectrum antimicrobial compounds such as Penicidin, Aromadendrene, Ethyl p-methoxycinnamate, 2-Coumaranone and 2-Methyl resorcinol.

CONCLUSION

These results have opened new avenues for discovery of novel antimalarial lead compounds from endophytic fungi associated with Annona muricata - a medicinally important plant.

Natural Peptides in Drug Discovery Targeting Acetylcholinesterase

Acetylcholinesterase-inhibitory peptide has gained much importance since it can inhibit acetylcholinesterase (AChE) and increase the availability of acetylcholine in cholinergic synapses, enhancing cholinergic transmission in pharmacological treatment of Alzheimer’s disease (AD). Natural peptides have received considerable attention as biologically important substances as a source of AChE inhibitors. These natural peptides have high potential pharmaceutical and medicinal values due to their bioactivities as neuroprotective and neurodegenerative treatment activities. These peptides have attracted great interest in the pharmaceutical industries, in order to design potential peptides for use in the prophylactic and therapy purposes. Some natural peptides and their derivatives have high commercial values and have succeeded in reaching the pharmaceutical market. A large number of peptides are already in preclinical and clinical pipelines for treatment of various diseases. This review highlights the recent researches on the various natural peptides and future prospects for AD management.

Characterization, culture medium optimization and antioxidant activity of an endophytic vitexin-producing fungus Dichotomopilus funicola Y3 from pigeon pea [Cajanus cajan (L.) Millsp.]

AIMS

The aim of this study was to characterize a fungal endophyte Y3 from pigeon pea (Cajanus cajan [L.] Millsp), as a novel producer of vitexin, and its culture medium optimization and antioxidant activity.

METHODS AND RESULTS

The endophyte from the leaves of pigeon pea was identified as Dichotomopilus funicola by the morphological and molecular characteristics. The most important medium variables affecting vitexin production in liquid culture of D. funicola Y3 were screened by Plackett-Burman design, and three culture medium constituents (i.e. l-phenylalanine, salicylic acid and CuSO₄ ·5H₂ O) were identified to play significant roles in vitexin production. The most significant factors were further optimized using by central composite design with response surface methodology. The DPPH radical-scavenging assay indicated that fungal vitexin exhibited notable antioxidant activity with an EC₅₀ value of 164 μg l^-1 .

CONCLUSIONS

First, a novel endophyte vitexin-producing Dichotomopilus funicola Y3 was isolated from pigeon pea (Cajanus cajan[L.] Millsp.). The maximum vitexin yield was obtained as 78·86 mg l^-1 under the optimum culture medium constituents: 0·06 g l^-1  l-phenylalanine, 0·21 g l^-1 salicylic acid, and 0·19 g l^-1 CuSO₄ ·5H₂ O in medium, which is 4·59-fold higher than that in the unoptimized medium. Also, fungal vitexin clearly demonstrated its antioxidant potential.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings provide an alternative source for large-scale production of vitexin by endophytic fungal fermentation and have a promising prospect in food and pharmaceutical industry.

Endophytic Fungi-Alternative Sources of Cytotoxic Compounds: A Review

Cancer is a major cause of death worldwide, with an increasing number of cases being reported annually. The elevated rate of mortality necessitates a global challenge to explore newer sources of anticancer drugs. Recent advancements in cancer treatment involve the discovery and development of new and improved chemotherapeutics derived from natural or synthetic sources. Natural sources offer the potential of finding new structural classes with unique bioactivities for cancer therapy. Endophytic fungi represent a rich source of bioactive metabolites that can be manipulated to produce desirable novel analogs for chemotherapy. This review offers a current and integrative account of clinically used anticancer drugs such as taxol, podophyllotoxin, camptothecin, and vinca alkaloids in terms of their mechanism of action, isolation from endophytic fungi and their characterization, yield obtained, and fungal strain improvement strategies. It also covers recent literature on endophytic fungal metabolites from terrestrial, mangrove, and marine sources as potential anticancer agents and emphasizes the findings for cytotoxic bioactive compounds tested against specific cancer cell lines.

Genome Sequence of an Endophytic Fungus, Fusarium solani JS-169, Which Has Antifungal Activity

An endophytic fungus, Fusarium solani strain JS-169, isolated from a mulberry twig, showed considerable antifungal activity. Here, we report the draft genome sequence of this strain. The assembly comprises 17 scaffolds, with an N₅₀ value of 4.93 Mb. The assembled genome was 45,813,297 bp in length, with a G+C content of 49.91%.

Bioprospecting of Endophytes for Agricultural and Environmental Sustainability

The term endophytes refers to a group of endosymbionts usually bacterium, fungus or interactive bacterium-fungal species residing asymptomatically and grows within plants for at least a part of their life cycle intra- and intercelullarly in the tissues of higher plants without causing any visible manifestation of disease. The endophytes represent a potential source of novel natural and ecofriendly products for medicinal, agricultural and industrial uses with least adverse effect on the environment.

The enormous biological diversity coupled with their capability to biosynthesize bioactive secondary metabolites has provided the momentum for the researchers working on endophytes. The present review was undertaken to highlight the biotechnological processes and bioprospection of endophytes as potential antimicrobial agents, secondary metabolites, antibiotics, antagonists against disease causing phytopathogens, cytotoxic, anticancer, insecticidal, antioxidant antiviral compounds andisolation and production of bioactive compounds with potent enzymatic activities.

Endophyte enhances biodegradation and hydrolysis processes significantly important against pathogenic infection, biotransformation studies and production of compounds with immense industrial applications. The interaction of the endophytic microbiota with the plants are more protected and can withstand the adverse environmental conditions and contribute to plant growth, productivity, carbon sequestration, enhanced phytoremediation efficiencies and amelioration of metal induced toxicity. The strategies governed by the endophytes for efficient production of novel bioactive phytocompounds was comprehensively discussed.

The review envisaged the biodiversity, transmission of endophytes, plant endophyte interactions for the production of bioactive compounds for therapeutic, environmental and agricultural sustainability.

Endophytic fungi associated with Taxus fuana (West Himalayan Yew) of Pakistan: potential bio-resources for cancer chemopreventive agents

CONTEXT

Endophytic fungi, being a prolific source of bioactive secondary metabolites, are of great interest for natural product discovery.

OBJECTIVE

Isolation and partial characterization of endophytic fungi inhabiting the leaves and woody parts of Taxus fuana Nan Li & R.R. Mill. (Taxaceae) and evaluation of biological activity.

MATERIALS AND METHODS

Endophytic fungal isolates were identified by molecular analysis of internal transcribed spacer (ITS) regions of 18S rDNA. Extracts of the endophytic fungi cultured on potato dextrose agar and modified medium were evaluated using cancer chemoprevention bioassays [inhibition of TNF-α-induced NFκB, aromatase and inducible nitric oxide synthase (iNOS); induction of quinone reductase 1 (QR1)] and growth inhibition with MCF-7 cells.

RESULTS

Nine of 15 fungal isolates were identified as belonging to Epicoccum, Mucor, Penicillium, Chaetomium, Paraconiothriym, Plectania or Trichoderma. Five of the 15 extracts inhibited NFκB activity (IC₅₀ values ranging between 0.18 and 17 μg/mL) and five inhibited iNOS (IC₅₀ values ranging between 0.32 and 12.9 μg/mL). In the aromatase assay, only two isolates mediated inhibition (IC₅₀ values 12.2 and 10.5 μg/mL). With QR1 induction, three extracts exhibited significant activity (concentrations to double activity values ranging between 0.20 and 5.5 μg/mL), and five extracts inhibited the growth of MCF-7 cells (IC₅₀ values ranging from 0.56 to 17.5 μg/mL). Six active cultures were derived from woody parts of the plant material.

CONCLUSION

The endophytic fungi studied are capable of producing pharmacologically active natural compounds. In particular, isolates derived from the wood of Taxus fuana should be prioritized for the isolation and characterization of bioactive constituents.

Endophytes: A Treasure House of Bioactive Compounds of Medicinal Importance

Endophytes are an endosymbiotic group of microorganisms that colonize in plants and microbes that can be readily isolated from any microbial or plant growth medium. They act as reservoirs of novel bioactive secondary metabolites, such as alkaloids, phenolic acids, quinones, steroids, saponins, tannins, and terpenoids that serve as a potential candidate for antimicrobial, anti-insect, anticancer and many more properties. While plant sources are being extensively explored for new chemical entities for therapeutic purposes, endophytic microbes also constitute an important source for drug discovery. This review aims to comprehend the contribution and uses of endophytes as an impending source of drugs against various forms of diseases and other possible medicinal use.

Biological Evaluation of Endophytic Fungus Chaetomium sp. NF15 of Justicia adhatoda L.: A Potential Candidate for Drug Discovery

Background

The endophytes of medicinal plants, such as Justicia adhatoda L., represent a promising and largely underexplored domain that is considered as a repository of biologically active compounds.

Objectives

The aim of present study was isolation, identification, and biological evaluation of endophytic fungi associated with the J. adhatoda L. plant for the production of antimicrobial, antioxidant, and cytotoxic compounds

Materials and Methods

Endophytic fungi associated with the J. adhatoda L. plant were isolated from healthy plant parts and taxonomically characterized through morphological, microscopic, and 18S rDNA sequencing methods. The screening for bioactive metabolite production was achieved using ethyl acetate extracts, followed by the optimization of different parameters for maximum production of bioactive metabolites. Crude and partially purified extracts were used to determine the antimicrobial, antioxidant, and cytotoxic potential

Results

Out of six endophytic fungal isolates, Chaetomium sp. NF15 showed the most promising biological activity and was selected for detailed study. The crude ethyl acetate extract of NF15 isolate after cultivation under optimized culture conditions showed promising antimicrobial activity, with significant inhibition of the clinical isolates of Staphylococcus aureus (87%, n=42), Pseudomonas aeruginosa (> 85%, n = 41), and Candida albicans (62%, n = 24).

Conclusions

The present study confirms the notion of selecting endophytic fungi of medicinal plant Justicia for the bioassay-guided isolation of its bioactive compounds, and demonstrates that endophytic fungus Chaetomium sp. NF15 could be a potential source of bioactive metabolites

Endophytic Actinobacteria from the Brazilian Medicinal Plant Lychnophora ericoides Mart. and the Biological Potential of Their Secondary Metabolites

Endophytic actinobacteria from the Brazilian medicinal plant Lychnophora ericoides were isolated for the first time, and the biological potential of their secondary metabolites was evaluated. A phylogenic analysis of isolated actinobacteria was accomplished with 16S rRNA gene sequencing, and the predominance of the genus Streptomyces was observed. All strains were cultured on solid rice medium, and ethanol extracts were evaluated with antimicrobial and cytotoxic assays against cancer cell lines. As a result, 92% of the extracts showed a high or moderate activity against at least one pathogenic microbial strain or cancer cell line. Based on the biological and chemical analyses of crude extracts, three endophytic strains were selected for further investigation of their chemical profiles. Sixteen compounds were isolated, and 3-hydroxy-4-methoxybenzamide (9) and 2,3-dihydro-2,2-dimethyl-4(1H)-quinazolinone (15) are reported as natural products for the first time in this study. The biological activity of the pure compounds was also assessed. Compound 15 displayed potent cytotoxic activity against all four tested cancer cell lines. Nocardamine (2) was only moderately active against two cancer cell lines but showed strong activity against Trypanosoma cruzi. Our results show that endophytic actinobacteria from L. ericoides are a promising source of bioactive compounds.

Spatial and seasonal influences on culturable endophytic mycobiota associated with different tissues of Eugenia jambolana Lam. and their antibacterial activity against MDR strains

BACKGROUND

Present study focuses on diversity and distribution analysis of endophytic fungi associated with different tissues of Eugenia jambolana. The influence of season and geographical location on diversity and distribution of endophytic fungi has been analyzed. Antibacterial activity of isolated fungal species has also been investigated against MDR bacterial strains.

RESULT

A total of 1896 endophytic fungal isolates were obtained from healthy, surface sterilized tissues of leaf, stem and petiole tissues during summer, monsoon and winter season. Out of 24 fungal species isolated, 20 species belong to class Ascomycetes, 2 to Basidiomycetes and 2 to Zygomycetes. Maximum species diversity was in rainy season whereas colonization frequency was in winter. All the diversity indices showed maximum species diversity at site 5 (Yamunanager), rainy among the seasons and leaf among the tissues studied. Aspergillus genus was most frequently isolated. Aspergillus niger and Alternaria alternata were most dominant species. Three way ANOVA results showed that effect of season was highly significant on species diversity in relation to sites and tissues. 60% endophytic fungal extracts showed significant antibacterial activity against one or more than one MDR bacterial strain.

CONCLUSION

Different fungal species were recovered from different sites but the inter-site comparisons were not significant according to Jaccard similarity coefficient. Diversity of such fungal endophytes indicates that Eugenia jambolana plant acts as an ecosystem facilitating survival of many microbes with impressive antibacterial potential.

Microbial Biotransformation to Obtain New Antifungals

Antifungal drugs belong to few chemical groups and such low diversity limits the therapeutic choices. The urgent need of innovative options has pushed researchers to search new bioactive molecules. Literature regarding the last 15 years reveals that different research groups have used different approaches to achieve such goal. However, the discovery of molecules with different mechanisms of action still demands considerable time and efforts. This review was conceived to present how Pharmaceutical Biotechnology might contribute to the discovery of molecules with antifungal properties by microbial biotransformation procedures. Authors present some aspects of (1) microbial biotransformation of herbal medicines and food; (2) possibility of major and minor molecular amendments in existing molecules by biocatalysis; (3) methodological improvements in processes involving whole cells and immobilized enzymes; (4) potential of endophytic fungi to produce antimicrobials by bioconversions; and (5) in silico research driving to the improvement of molecules. All these issues belong to a new conception of transformation procedures, so-called "green chemistry," which aims the highest possible efficiency with reduced production of waste and the smallest environmental impact.

Alkaloid (Meleagrine and Chrysogine) from endophytic fungi (Penicillium sp.) of Annona squamosa L

Several endophytic fungal strains from Srikaya plants (Annona squamosa L.) have been isolated and one of them was identified as Penicillium sp. Penicillium has been proven as an established source for a wide array of unique bioactive secondary metabolites that exhibit a variety of biological activities. The aim of this study is isolation of secondary metabolite from Penicillium, an endophytic of A. squamosa L. Penicillium sp. from endophytic of A. squamosa L. was fermented in Wicherham media. The whole extract from both liquid media and mycelium was partitioned by ethyl acetate and evaporated to obtain crude ethyl acetate extract. The ethyl acetate extract was then brokedown using column chromatography with silica as stationary phase and mixture of ethyl acetate/methanol (98%:2%) as mobile phase and then was separated by sephadex column. Structure elucidation of isolated compounds were mainly done by analysis of one and two dimensional NMR (Nuclear Magnetic Resonance) data and supported by HPLC (High performance Liquid Chromatography) and MS-TOF (Mass Spectrometer-Time of Flight). Isolated secondary metabolites were tested using in vitro assays for anticancer and antimicrobial activity. For anticancer activity, the metabolites were tested against breast cancer cells (MCF-7) using MTT assay, while for antimicrobial activity was performed using disk diffusion assays. From these physical, chemical and spectral evidences that the secondary metabolites were confirmed as Chrysogine and Meleagrine. Chrysogine and Meleagrine have no activity as anticancer and antimicrobial.

Impact of endophytic microorganisms on plants, environment and humans

Endophytes are microorganisms (bacteria or fungi or actinomycetes) that dwell within robust plant tissues by having a symbiotic association. They are ubiquitously associated with almost all plants studied till date. Some commonly found endophytes are those belonging to the genera Enterobacter sp., Colletotrichum sp., Phomopsis sp., Phyllosticta sp., Cladosporium sp., and so forth. Endophytic population is greatly affected by climatic conditions and location where the host plant grows. They produce a wide range of compounds useful for plants for their growth, protection to environmental conditions, and sustainability, in favour of a good dwelling place within the hosts. They protect plants from herbivory by producing certain compounds which will prevent animals from further grazing on the same plant and sometimes act as biocontrol agents. A large amount of bioactive compounds produced by them not only are useful for plants but also are of economical importance to humans. They serve as antibiotics, drugs or medicines, or the compounds of high relevance in research or as compounds useful to food industry. They are also found to have some important role in nutrient cycling, biodegradation, and bioremediation. In this review, we have tried to comprehend different roles of endophytes in plants and their significance and impacts on man and environment.