Fernanda O. Chagas

Endophytic fungi found in association with Smallanthus sonchifolius (Asteraceae) as resourceful producers of cytotoxic bioactive natural products

Smallanthus sonchifolius is a traditional Andean plant which has been cultured mainly in Brazil, Japan and New Zealand due to its medicinal properties. A study of the endophytic fungi associated to the plant was carried out in order to characterize new cytotoxic agents. Thirty two fungal strains were isolated and submitted to cultivation and extraction producing 186 extracts. Of these, 12% displayed moderate to high cytotoxic activities and were considered promising anticancer compound sources. The ethyl acetate fractions of Nigrospora sphaerica and Phoma betae liquid fermentations contained the synergistic compounds 8‐hydroxy‐6‐methoxy‐3‐methylisocoumarin and (22E,24R)‐ergosta‐4,6,8(14),22‐tetraen‐3‐one which are potential compounds for drug discovery. Another isolated compound, pimara‐7,15‐dien‐3‐β‐ol diterpene is being characterized for the first time through a detailed spectroscopic analysis including GC/MS, homo‐ and hetero‐nuclear correlated NMR experiments (HMQC, HMBC, COSY and NOEdiff) along with its optical rotation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Mixed Culture of Endophytic Fungi Increases Production of Antifungal Polyketides

Secondary metabolites produced by endophytic microorganisms can provide benefits to host plants, such as stimulating growth and enhancing the plant’s resistance toward biotic and abiotic factors. During its life, a host plant may be inhabited by many species of endophytes within a restrictive environment. This condition can stimulate secondary metabolite production that improves microbial competition and may consequently affect both the neighboring microorganisms and the host plant. The interactions between the endophytes that co-habit the same host plant have been studied. However, the effect of these interactions on the host plant has remained neglected. When using mixed microbial cultures, we found that the endophytic fungus Alternaria tenuissima significantly increased the production of some polyketides, including antifungal stemphyperylenol in response to the endophytic Nigrospora sphaerica. Biological activity assays revealed that stemphyperylenol can cause cytotoxic effects against N. sphaerica, although no phytotoxicity was observed in the host plant Smallanthus sonchifolius, even at concentrations much higher than those toxic to the fungus. The polyketides produced by A. tenuissima may be important for the ecological relationships between endophyte-endophyte and endophytes-host plants in the natural environment.

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.

Endophytic Fungi as a Source of Novel Metabolites

Microorganisms inhabiting plant tissues without causing any damage to their host plant are referred to as endophytes and can be fungi or bacteria, including actinobacteria. Due to a direct interaction between plant and endophytes, these microorganisms are an interesting source for biologically active natural products. Here, we reviewed the novel compounds isolated from endophytic fungi from 2012 to April 2014, mentioning their biological activities as well as their biological sources. Only secondary metabolites containing any interesting structural novelty or relevant biological activity were highlighted. The novel metabolites were classified into four major groups based on their biosynthetic pathway, such as polyketide and fatty acid, phenylpropanoid, and terpenoid derivatives as well as N-containing compounds. Taking into account that laboratorial conditions may lead to a minimal or absent production of many interesting microbial metabolites produced by the endophytes while interacting in their natural habitat, some approaches have been applied to the endophytes cultures and some examples of new metabolites obtained by using those strategies are also mentioned.

Amphotericin B as an inducer of griseofulvin-containing guttate in the endophytic fungus Xylaria cubensis FLe9

Microorganisms interact with each other via metabolic exchange. Several studies have revealed that microbial metabolites may act as mediators of microbial interactions. During our previous work with endophytes isolated from the Brazilian medicinal plant Lychnophora ericoides, we demonstrated that the well-known antifungal compound amphotericin B, produced by the endophytic actinobacterium Streptomyces albospinus RLe7, may trigger chemical responses in endophytic fungi. In this study, we cultured endophytic fungi in amphotericin B-enriched media to verify whether other chemical responses could be induced. Interestingly, one fungal strain showed a differential response under the tested conditions. When the fungus Xylaria cubensis FLe9 was cultured in amphotericin B-enriched media, a mycelial guttate was observed. Investigation of the fungal extracts from X. cubensis FLe9 and purification of fungal metabolites were performed using high-performance liquid chromatography coupled to a diode array detector. Isolated compounds were characterized on the basis of nuclear magnetic resonance and mass spectrometry data. Therefore, we report on the overproduction of the fungal metabolites griseofulvin (1) and dechlorogriseofulvin (2) when the endophytic fungus Xylaria cubensis FLe9 was exposed to amphotericin B. Both fungal compounds 1 and 2 were also detected in the mycelial guttate produced when X. cubensis FLe9 was exposed to amphotericin B. Since the amphotericin B-producing actinobacterium S. albospinus RLe7 and the griseofulvin-producing fungus X. cubensis FLe9 are endophytes from the same host, biosynthetic induction of fungal compounds may suggest a potential signaling role for amphotericin B in natural environments. However, this hypothesis needs to be further investigated in field experiments.

Genome Sequence of Streptomyces sp. Strain RTd22, an Endophyte of the Mexican Sunflower

ABSTRACT We report here the complete genome sequence of Streptomyces sp. strain RTd22, an endophytic actinobacterium that was isolated from the roots of the Mexican sunflower Tithonia diversifolia. The bacteriums 11.1-Mb linear chromosome is predicted to encode a large number of unknown natural products.

The semisynthetic landscape of aphidicolin: inspiration towards leishmanicidal compounds

Recentes estudos demonstraram que afidicolina, metabolito secundario do fungo endofitico Nigrospora sphaerica, apresenta alta atividade contra o protozoario Leishmania major. Apesar do promissor potencial leishmanicida, a afidicolina apresenta propriedades fisico-quimicas e perfil farmacocinetico inadequado para terapeutica. Neste sentido, uma revisao da literatura apresenta as limitadas modificacoes para este terpeno e ainda traz informacoes sobre as propriedades moleculares dos compostos ja descritos e sua correlacao com compostos leishmanicidas. Essa revisao forneceu uma analise racional para o desenvolvimento do derivado oxima. Uma serie de derivados da afidicolina bem como o analogo oxima foram sintetizados para avaliacao preliminar dos requisitos estruturais para atividade leishmanicida da afidicolina e seus derivados semisinteticos. Oito compostos foram sintetizados e testados contra diferentes especies de Leishmania. A avaliacao preliminar demonstrou alta atividade leishmanicida da afidicolina enquanto que o derivado oxima apresenta moderada seletividade contra a especie L. braziliensis, endemica em diversos paises da America do Sul. Nenhum dos compostos apresentou citotoxicidade contra celulas de mamiferos. Recent studies have shown that aphidicolin, a secondary metabolite of the endophytic fungus Nigrospora sphaerica, has high activity against the protozoan Leishmania major. Despite its promising leishmanicidal potential, aphidicolin presents a therapeutically unsuitable physicochemical and pharmacokinetic profile. In this sense, a review of the literature shows the limited types of modification for this terpene. In addition, it gives an idea about the molecular properties of the compounds produced and which were correlated to leishmanicidal derivatives. This analysis provided us a rationale for the development of an oxime derivative. We synthesized the oxime-aphidicolin and a series of derivatives for a preliminary evaluation of the structural requirements for the leishmanicidal activity of aphidicolin and its semisynthetic derivatives. Eight compounds have been synthesized and tested against different species of the Leishmania protozoa. The preliminary evaluation demonstrated high leishmanicidal activity for aphidicolin, while the oxime derivative shows moderate selectivity for the L. braziliensis species, which is commonly found in several South American countries. None of the compounds showed cytotoxicity against mammalian cells.

Chemical interaction of endophytic fungi and actinobacteria from Lychnophora ericoides in co-cultures

Microorganisms interact chemically in natural environments; however, the compounds and mechanisms involved in this phenomenon are still poorly understood. Using the cocultivation approach, changes in metabolic profiles due to interactions between endophytic fungal and actinobacterial strains isolated from the plant Lychnophora ericoides (Asteraceae) were assessed. The production of the cytotoxic compound cytochalasin H by the fungus Phomopsis sp. FLe6 was remarkably inhibited in solid and liquid co-cultures with the actinobacteria Streptomyces albospinus RLe7. This was a consequence of the fungal growth inhibition caused by antifungal compounds produced by S. albospinus RLe7, including amphotericin B. Cytochalasin H is not toxic to S. albospinus RLe7, suggesting that this microorganism does not require a defense mechanism to prevent the potentially harmful effects of such fungal compound. By exhibiting various competitive phenotypes, these microbes can control each others growth when sharing an environment.