Abstract:In the past few decades groups of scientists have focused their study on relatively new microorganisms called endophytes. By definition these microorganisms, mostly fungi and bacteria, colonise the intercellular spaces of the plant tissues. The mutual relationship between endophytic microorganisms and their host plants, taxanomy and ecology of endophytes are being studied. Some of these microorganisms produce bioactive secondary metabolites that may be involved in a host-endophyte relationship. Recently, many endophytic bioactive metabolites, known as well as new substances, possesing a wide variety of biological activities as antibiotic, antitumor, antiinflammatory, antioxidant, etc. have been identified. The microorganisms such as endophytes may be very interesting for biotechnological production of bioactive substances as medicinally important agents. Therefore the aim of this review is to briefly characterize endophytes and summarize the structuraly different bioactive secondary metabolites produced by endophytic microorganisms as well as microbial sources of these metabolites and their host plants.

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A mixture of related metabolites (denoted OR-1) was isolated from the fermentation broth of Penicillium funiculosum together with mitorubrinic acid. Structurally OR-1 is glyceric acid esterified with C14-C18 fatty acids. Steady-state studies revealed that OR-1 behaved like an uncompetitive trypsin inhibitor with Ki 17.6 mumol/L.

L-Methionine and DL-ethionine decreased production of thiolutin and aureothricin in Streptomyces kasugaensis. In the presence of L-methionine the culture also produced 3-methylthioacrylic acid, 3-methylthiopropionic acid and 3,6-bis-(2-methylthioethyl)-2,5-dioxopiperazine. Production of the metabolites depended on the concentration of L-methionine in the medium.

In the course of study of epiphytic microorganisms occurring on the surface of roots of Taxus baccata L. a new strain Streptomyces sp. AC113 was isolated. According to 16S ribosomal DNA-based identification the new strain is 99% identical with Streptomyces flavidofuscus. This strain cultivated in an arginine glycerol medium produced three major metabolites identified as (-)-8-O -methyltetrangomycin (1), 8-O -methyltetrangulol (2) and 8-O -methyl-7-deoxo-7-hydroxytetrangomycin (3). The chemical structures of these angucyclines were elucidated by 1D and 2D NMR as well as by mass spectrometry. Isolated angucycline metabolites showed significant antimicrobial activity against Bacillus cereus and Listeria mocytogenes. Cytotoxic activities of compounds 1, 2 and 3 against four cell lines (B16, HT-29 and non - tumor V79, L929) were evaluated. Compound 3 was the most potent anticancer agents with IC(50) 0.054 microg/ml against cell line B16.