Investigation of Queensland dry rainforest endophyte and their production of antimicrobial agents

Investigation of Queensland dry rainforest endophyte and their production of antimicrobial agents

Endophytic fungi are organisms that colonise the tissues of most plants without causing obvious disease symptoms in the host. Endophytic fungi represent a significant proportion of undocumented global mycological diversity and are not well studied in Australia. It is likely that Australian plants house a wealth of undescribed endophytic fungal species and these endophytic species could be valuable sources of novel bioactive compounds. In this project, endophytic fungi were investigated in multiple semi-evergreen vine thickets, a threatened type of dry rainforest, in southeast Queensland, Australia. A total of 244 fungal endophytes were isolated from 22 plant species. Both morphological and molecular (sequencing of ITS DNA) taxonomic approaches were used for identification of the endophytic fungal isolates. Species of Nigrospora, Alternaria, Xylaria, Phomopsis and Preussia were the most common taxa isolated. Endophytic fungi were screened for potential antimicrobial activity against bacterial and fungal taxa. Six fungal endophytes consistently reduced the growth of one or more of these test microbes and these were then further grown in bulk quantities. Ethyl acetate crude extracts of the bioactive endophytes were retested against the test microbes and isolates of Preussia (two species), Coniochaeta, Hypoxylon and Xylaria continued to show bioactivity. HPLC fractions of the bulk extracts from the Coniochaeta sp. and Preussia sp. 2 were retested for antimicrobial activity and both of these continued to show bioactivity. Further fractionation and mass spectroscopic analysis indicated the possible presence of a bioactive peptide in Preussia sp. 2. These two endophyte taxa were further characterised taxonomically through sequencing of LSU DNA and induction of teleomorph states. Possible modes of action of the bioactive compounds from the two taxa were investigated by analysing cell structures in inhibited cells via fluorescence and electron microscopy. These investigations demonstrate that Australian semi-evergreen vine thickets house a range of previously undescribed fungal endophyte taxa and that a number of these may contain antimicrobial compounds.

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