Insecticidal Endostemonines A-J Produced by Endophytic Streptomyces from Stemona sessilifolia

Sinoflavonoids NJ and NK, anti-inflammatory prenylated flavonoids from the fruits of Podophyllum hexandrum Royle

Two new prenylated flavonoids named sinoflavonoids NJ and NK (1-2), along with ten known compounds were isolated from the fruits of Podophyllum hexandrum Royle. The chemical structures were determined through NMR spectroscopic data and MS analysis. Sinoflavonoid NJ (1) with an unusual 5,11-dioxabenzo[b]fluoren-10-one skeleton was firstly reported from Berberidaceae. The isolated flavonoids were tested with LPS-induced RAW 264.7 mouse macrophages model for their anti-inflammatory activity. Sinoflavonoid NJ (1) showed the most potent inhibition on nitric oxide production with IC50 value as 0.06 μM.

Unlocking the potential of bacterial endophytes from medicinal plants for drug discovery

Among the plant-associated microorganisms, the so-called endophytes continue to attract much attention because of their ability not only to protect host plants from biotic and abiotic stress factors, but also the potential to produce bioactive secondary metabolites. The latter property can elicit growth-promoting effects on plants, as well as boost the production of plant-specific secondary metabolites with valuable pharmacological properties. In addition, endophyte-derived secondary metabolites may be a rich source for the discovery of drugs to treat various diseases, including infections and cancer. However, the full potential of endophytes to produce bioactive secondary metabolites is often not revealed upon conventional cultivation in the laboratory. New advances in genomics and metabolic engineering offer exciting opportunities for the exploration and exploitation of endophytes' biosynthetic potential. This review focuses on bacterial endophytes of medicinal plants, some of their secondary metabolites and recent advances in deciphering their biosynthesis. The latter may assist in genetic engineering efforts aimed at the discovery of novel bioactive compounds with the potential to be developed into drugs.

Insecticidal potential of endophytic Streptomyces sp. against Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) and biosafety evaluation

Fruit flies of Tephritidae family pose a serious threat to cultivation of fruits and vegetables across the world. Among them, melon fruit fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) is a devastating pest of plants from Cucurbitaceae family. In a rising concern about the harmful effects associated with the use of chemical insecticides and development of resistance in pest insects, safer pest management strategies such as, use of biopesticides of microbial origin are being contemplated. Therefore, the present study aimed to evaluate the insecticidal potential of Streptomyces sp. SP5 protein extract against Z. cucurbitae. MTT assay, Ames mutagenicity, DNA nicking, and comet assay were conducted to determine the biosafety of protein extract. Second instar larvae of Z. cucurbitae were treated with various concentrations (1, 100, 200, 300, 400, and 500 μg/ml) of Streptomyces sp. SP5 protein extract. The protein extract showed significant larvicidal effects with LC50 value of 308.92 μg/ml. The percentage of adults emerged declined with increase in concentration. There was significant prolongation in developmental durations of the larvae. Various morphological aberrations in the form of deformed adults and pupae and decline in pupal weight were also observed. The nutritional physiology of the treated larvae was also adversely affected. The results from biosafety evaluation revealed antimutagenic and non-toxic nature of Streptomyces sp. proteins. This study indicates that Streptomyces sp. SP5 has the potential to be used as an ecologically safe biocontrol agent against Z. cucurbitae.

Endophytic Microbes from Medicinal Plants in Fenghuang Mountain as a Source of Antibiotics

One of the largest concerns with world health today is still antibiotic resistance, which is making it imperative to find efficient alternatives as soon as possible. It has been demonstrated that microbes are reliable sources for the creation of therapeutic antibiotics. This research intends to investigate the endophytic microorganisms from several medicinal plants in Fenghuang Mountain (Jiangsu Province, China) and to discover new antibiotics from their secondary metabolites. A total of 269 endophytic strains were isolated from nine distinct medicinal plants. Taxonomic analysis revealed that there were 20 distinct species among these endophytes, with Streptomyces being the most common genus. Three of the target strains were chosen for scale-up fermentation after preliminary screening of antibacterial activities and the metabolomics investigation using LC-MS. These strains were Penicillium sp. NX-S-6, Streptomyces sp. YHLB-L-2 and Streptomyces sp. ZLBB-S-6. Twenty-three secondary metabolites (1-23), including a new sorbicillin analogue (1), were produced as a result of antibacterial activity-guided isolation. Through spectroscopic analysis using MS and NMR, the structures of yield compounds were clarified. According to antibacterial data, S. aureus or B. subtilis were inhibited to varying degrees by sorrentanone (3), emodic acid (8), GKK1032 B (10), linoleic acid (14), toyocamycin (17) and quinomycin A (21). The most effective antimicrobial agent against S. aureus, B. subtilis, E. coli and A. baumannii was quinomycin A (21). In addition, quinomycin A showed strong antifungal activity against Aspergillus fumigatus, Cryptococcus neoformans, and two clinical isolated strains Aspergillus fumigatus #176 and #339, with MIC as 16, 4, 16 and 16 µg/mL, respectively. This is the first time that bioprospecting of actinobacteria and their secondary metabolites from medicinal plants in Fenghuang Mountain was reported. The finding demonstrates the potential of endophytic microbes in medical plants to produce a variety of natural products. Endophytic microbes will be an important source for new antibiotics.

Discovery and Biosynthetic Studies of a Highly Reduced Cinnamoyl Lipid, Tripmycin A, from an Endophytic Streptomyces sp

A Tripterygium wilfordii endophyte, Streptomyces sp. CB04723, was shown to produce an unusually highly reduced cytotoxic cinnamoyl lipid, tripmycin A (1). Structure-activity relationship studies revealed that both the cinnamyl moiety and the saturated fatty acid side chain are indispensable to the over 400-fold cytotoxicity improvement of 1 against the triple-negative breast cancer cell line MDA-MB-231 compared to 5-(2-methylphenyl)-4-pentenoic acid (2). Bioinformatical analysis, gene inactivation, and overexpression revealed that Hxs15 most likely acted as an enoyl reductase and was involved with the side chain reduction of 1, which provides a new insight into the biosynthesis of cinnamoyl lipids.

Endophytic actinobacteria from wild medicinal plants are a natural source of insecticide to control the African cotton leafworm (Spodoptera littoralis)

Insecticide resistance in agricultural pests has prompted the need to discover novel compounds with new modes of action. We investigated the potency of secondary metabolites from seventy endophytic actinobacteria against laboratory and field strains of Spodoptera littoralis (fourth instar), comparable to the bioinsecticide spinetoram (Radiant SC 12%). Endophytes from Artemisia herba-alba and A. judaica were highly effective. Chemical profiling of the most potent metabolite of the strain Streptomyces sp. ES2 was investigated using LC-QTOF-MS-MS technique, and the activity was validated through molecular docking studies. Metabolic extracts from actinobacteria belonging to Streptomyces, Nocardioides, and Pseudonocardia showed immediate and latent death to the Spodoptera littoralis fourth instar larvae. The metabolite from strain ES2 has shown the most promising and significant histopathological and inhibitory effects on the fourth instar larvae. ES2 metabolite caused lesions in the body wall cuticle, indicating a different mode of action than that of Radiant. Chemical profiling of ES2 showed the presence of cyromazine (molt inhibitor), 4-nitrophenol, and diazinon as key constituents. In conclusion, these findings suggest that secondary metabolites from endophytic actinobacteria inhabiting wild medicinal plants can be a sustainable source for promising natural biocontrol agents. This is the first illustration of the insecticidal activity of Artemisia spp. microbiome, and natural cyromazine synthesis by actinobacteria.

Extraction, structural characterization, and biological activities of a new glucan from Codonopsis pilosula

In this study, a powerful and rapid aqueous two-phase system (ATPS) method was used to extract polysaccharides from Codonopsis pilosula. The ATPS process was investigated with response surface methodology (RSM). At an ammonium sulfate concentration of 17%, ethanol concentration of 30%, and extraction temperature of 40 °C at pH 6, the total extraction yield of polysaccharides reached (31.57 ± 1.28)%. After separation and purification, a homogenized polysaccharide CPP 2-4 with molecular weight of 3.9 × 10⁴ kDa was obtained from the bottom phase. The physicochemical properties and structural features confirmed that CPP 2-4 was an α-1,6-glucan. Activity studies showed that the IC₅₀ of CPP 2-4 for DPPH radical scavenging was 0.105 mg/mL. The FRAP and ABTS assays showed that CPP 2-4 had strong antioxidant activity in a dose-dependent manner. Furthermore, CPP 2-4 inhibited NO release in RAW264.7 cells induced by lipopolysaccharide, which indicated a certain anti-inflammatory effect. This study improved the extraction rate of polysaccharides from C. pilosula and identified a glucan for the first time, that can contribute to a better understanding of the composition and structure of polysaccharides from C. pilosula and provide data support for the medicine and food homology of C. pilosula.

Macrolides from Streptomyces sp. SN5452 and Their Antifungal Activity against Pyricularia oryzae

Pyricularia oryzae causes rice blast, the major destructive disease in nearly all rice fields. In order to obtain highly active compounds against P. oryzae, four new 20-membered macrolides named venturicidins G–J (1–4) were isolated from the culture broth of Streptomyces sp. SN5452 along with two known ones, venturicidins A (5) and B (6). Their structures were determined by the cumulative analyses of nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry (HRESIMS) data. All isolated compounds were evaluated for their antifungal activity against P. oryzae. Interestingly, these compounds exhibited obvious inhibition to mycelial growth and conidial germination of P. oryzae. Remarkably, the EC₅₀ values of venturicidins A (5), B (6), and I (3) against mycelial growth were 0.11, 0.15 and 0.35 µg/mL, and their EC₅₀ values of conidial germination were 0.27, 0.39 and 1.14 µg/mL, respectively. The analysis of structure-activity relationships (SARs) revealed that the methylated positions might be involved in the antifungal activity of venturicidins. These results indicate that the venturicidins are prospective candidates for novel fungicides that can be applied in controlling rice blast.

Huoshanmycins A‒C, New Polyketide Dimers Produced by Endophytic Streptomyces sp. HS-3-L-1 From Dendrobium huoshanense

Three new polyketide dimers named huoshanmycins A‒C (1–3) were isolated from a plant endophytic Streptomyces sp. HS-3-L-1 in the leaf of Dendrobium huoshanense, which was collected from the Cultivation base in Jiuxianzun Huoshanshihu Co., Ltd. The dimeric structures of huoshanmycins were composed of unusual polyketides SEK43, SEK15, or UWM4, with a unique methylene linkage. Their structures were elucidated through comprehensive 1D-/2D-NMR and HRESIMS spectroscopic data analysis. The cytotoxicity against MV4-11 human leukemia cell by the Cell Counting Kit-8 (CCK8) method was evaluated using isolated compounds with triptolide as positive control (IC₅₀: 1.1 ± 0.4 μM). Huoshanmycins A and B (1, 2) displayed moderate cytotoxicity with IC₅₀ values of 32.9 ± 7.2 and 33.2 ± 6.1 μM, respectively.

Terragines F-G produced by endophytic Bacillus sp. SH-1.2-ROOT-18 from Dendrobium officinale

Two new terragine analogs (1‒2) with special succinimide and aminopentane moieties were isolated from the fermentation broth of Bacillus sp. SH-1.2-ROOT-18, an endophyte previously discovered from the root of Dendrobium officinale. The structures were elucidated base on comprehensive 1 D/2D NMR and MS data analysis. Complete NMR assignments for the first reported naturally occurring metabolite 3 was also provided.

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.

Streptomyces from traditional medicine: sources of new innovations in antibiotic discovery

Given the increased reporting of multi-resistant bacteria and the shortage of newly approved medicines, researchers have been looking towards extreme and unusual environments as a new source of antibiotics. Streptomyces currently provides many of the world's clinical antibiotics, so it comes as no surprise that these bacteria have recently been isolated from traditional medicine. Given the wide array of traditional medicines, it is hoped that these discoveries can provide the much sought after core structure diversity that will be required of a new generation of antibiotics. This review discusses the contribution of Streptomyces to antibiotics and the potential of newly discovered species in traditional medicine. We also explore how knowledge of traditional medicines can aid current initiatives in sourcing new and chemically diverse antibiotics.

New peptidendrocins and anticancer chartreusin from an endophytic bacterium of Dendrobium officinale

Background

Endophyte has now become a potential source for the discovery of novel natural products, as they participate in biochemical pathways of their hosts and produce analogous or novel bioactive compounds. As an epiphytic plant, Dendrobium officinale is one of precious Chinese medicines with various activities. It is well known for containing diverse endophytes, but so far not much is known about their secondary metabolites.

Methods

the plant tissues were cut and cultured on agar plates to isolate and purify the endophytic bacteria from Dendrobium officinale. Taxonomical identification of strains was performed by 16s rRNA. At the same time, the crude extracts of the strains were tested for antibacterial and cytotoxic activities to screen out one endophyte, Streptomyces sp. SH-1.2-R-15 for further study. After scale-up fermentation, isolation, purification and structure elucidation by using MS, 1D/2D-NMR spectroscopic method, secondary metabolites were identified and submitted for biological activity test.

Results

Fifty-eight endophytic strains representing 9 genera were obtained, with 50% of strains were Streptomyces. One of the most active strain, Streptomyces sp. 1.2-R-15, was selected for bioassay-guided isolation, which led to the discovery of two new peptide-type compounds 1 and 2, as well as a bioactive chartreusin, and four other known natural products. Their structures were determined by comprehensive spectroscopic techniques. Chartreusin showed potent cytotoxicity against Hep3B2.1-7 (IC₅₀ =18.19 µM) and H1299 (IC₅₀ =19.74 µM) cancer cell lines, and antibacterial activity against S. aureus (IC₅₀ =23.25 µM).

Conclusions

This study highlights the endophytic bacteria from medical plant D. officinale have potential bioactivity and natural product diversity, thus implicates them as a valuable source for new anticancer and antibiotics agents.