Microbial Interactions Involving the Endophytic Microorganisms Streptomyces Albospinus RLe7 and Colletotrichum Boninense FLe8.1

The ecological role of natural products in mediating microbial interactions is poorly understood. Endophytic microorganisms live inside tissue plants in a close relationship to each other; therefore they constitute interesting biological systems to study chemical ecology of natural products. The interaction between Streptomyces albospinus RLe7 and Colletotrichum boninense FLe8.1, endophytic microorganisms from Lychnophora ericoides, has been studied on solid and liquid co-cultures, using micro-extraction procedures and LC-MS/MS analyses. The experiments showed that S. albospinus RLe7 inhibits the growth of C. boninense FLe 8.1 in solid medium by the diffusion of secondary metabolites. The interaction between these endophytic microorganisms was studied by using mass spectrometry. Fragmentation studies lead to the identification of physostigmine, as the main compound being produced by S. albospinus RLe 7, and its N-ethyl analogue. These compounds diffused until the fungus mycelium in the co-culture interaction suggesting their possible role in the inhibition of the fungal growth. However, inhibition assays by microdilution against the fungus using pure physostigmine showed no considerable antifungal activity. Therefore, other compounds might also be involved in the antagonistic activity. Physostigmine is a well-known plant-derived acetylcholinesterase inhibitor and already isolated from soil actinobacteria. However, its biological function in the interaction with other microorganisms is unknown yet. Ongoing microbial interactions involving these endophytic microorganisms are being done and the results will be presented.