Tetramic acid based alkaloids from Aspergillus amoenus Roberg strain UP197 - antibiotic properties and new pyranterreones

The fungus Aspergillus amoenus Roberg strain UP197 was shown to produce antibacterial tetramic acid based alkaloids. Two new compounds, pyranterreone I and J (1 and 2), were isolated and characterized, in addition to the known compounds cordylactam, 7-hydroxycordylactam, pyranterreone C, D, F and G. Neither the pyranterreones nor the cordylacctams had previously been tested for antimicrobial activity. Thus, all isolated compounds were tested against a panel of clinically important bacteria and fungi. Pyranterreone C was active against Gram-positive and Gram-negative bacteria, with minimal inhibitory concentrations (MIC) between 1 and 8 µg/mL, whereas the MICs for all other compounds were >32 µg/mL. Pyranoterreone C was cytotoxic towards HepG2 cells, and since pyranterreone C reacted rapidly with the nucleophile cysteine, it is likely that the observed antibacterial activity is due to the chemical reactivity rather than enzymatic affinity, making it unsuitable for development as an antibacterial drug.

Discovery and Characterization of a PKS-NRPS Hybrid in Aspergillus terreus by Genome Mining

Fungal polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) hybrids have been characterized to produce polyketide-amino acid compounds with striking structural features and biological activities. In this study, a PKS-NRPS hybrid enzyme was found in Aspergillus terreus by genome mining. By activating the cluster-specific transcriptional regulator, this cryptic PKS-NRPS gene cluster was successfully activated and ten products (1-10) were identified as pyranterreones. Using functional genetics, bioinformatics, and isotope-labeling feeding analysis, the biosynthetic pathway was revealed. This is the second PKS-NRPS hybrid identified in A. terreus.