Genomic and chromatographic approach for the discovery of polyketide antimicrobial metabolites from an endophytic Phomopsis liquidambaris CBR-18

New approaches in probing for antimicrobial metabolites require genome and chemical investigation. The rapid identification of known compounds, i.e. dereplication, is strategically crucial in bioprospecting microbes for novel metabolites. An endophytic fungal strain, CBR-18, was isolated from Cryptolepis buchanani Roem. and identified as Phomopsis liquidambaris by molecular analysis. Biosynthetic polyketide synthase (PKS) genes of CBR-18 were investigated using three sets of degenerate primers, amplified with LC1–LC2c primers. Type I PKS gene-based and chemical investigation by a chromatography-guided approach furnished a broad-spectrum antimicrobial metabolite which was identified as oblongolide Y. Minimum inhibitory concentration values of the compound against test pathogens ranged between 25 and 100 µg/ml. The present study highlights the utility of strain CBR-18 as a promising source of potential polyketide antimicrobial agents which could be exploited for industrial purposes. This approach enabled different ketosynthase domains to be targeted for the isolation of previously uncharacterized bioactive polyketides, and could be used as a method for the rapid screening of fungal endophytes capable of producing potential polyketide antimicrobial agents.