Combined genetic and bioactivity-based prioritization leads to the isolation of an endophyte-derived antimycobacterial compound

Aim: To initiate a genetic and bioactivity-based screening programme of culturable endophytes to identify micro-organisms capable of producing bioactive polyketides and peptides.

Methods and Results: Fungal endophytes were isolated from flowers, leaves and roots of Rhoeo spathacea, revealing a community consisting of Colletotrichum sp., Fusarium sp., Guignardia sp., Phomopsis sp., Phoma sp. and Microdochium sp. Genetic screening showed that all isolates had polyketide synthase (PKS) genes and most had nonribosomal peptide synthetase (NRPS) genes. Ethyl acetate extracts of the fungal isolates exhibited antiproliferative activity against at least one of the seven bacterial and mycobacterial test strains. Nuclear Magnetic Resonance -guided fractionation of the crude extract from a Fusarium sp. strain which exhibited strong antiproliferative activity against Mycobacterium tuberculosis resulted in the isolation of the polyketide javanicin. This compound was active against Myco. tuberculosis (MIC = 25 μg ml^-1) and Mycobacterium phlei (MIC = 50 μg ml^-1).

Conclusions: The medicinal plant R. spathacea hosts a variety of fungal endophytes capable of producing antibacterial and antimycobacterial compounds. There is a positive correlation between the presence of PKS and/or NRPS encoding genes in endophytes and the bioactivity of their respective organic extracts.

Significance and Impact of the Study: This is the first report on the fungal endophytic diversity of R. spathacea, and the isolation of an antimycobacterial compound from the plant which has been traditionally used for the treatment of tuberculosis symptoms.