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 other's growth when sharing an environment.

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.