Polyketide synthases (PKSs) and/or nonribosomal peptide synthetases (NRPSs) are central components of secondary metabolism in bacteria, plants, and fungi. In filamentous fungi, diverse PKSs and NRPSs participate in the biosynthesis of secondary metabolites such as pigments, antibiotics, siderophores, and mycotoxins. However, many secondary metabolites as well as the enzymes involved in their production are yet to be discovered. Both PKSs and NRPSs require activation by enzyme members of the 4′-phosphopantetheinyl transferase (PPTase) family. Here, we report the isolation and characterization of Aspergillus nidulans strains carrying conditional ( cfwA2 ) and null (Δ cfwA ) mutant alleles of the cfwA gene, encoding an essential PPTase. We identify the polyketides shamixanthone, emericellin, and dehydroaustinol as well as the sterols ergosterol, peroxiergosterol, and cerevisterol in extracts from A. nidulans large-scale cultures. The PPTase CfwA/NpgA was required for the production of these polyketide compounds but dispensable for ergosterol and cerevisterol and for fatty acid biosynthesis. The asexual sporulation defects of cfwA , Δ fluG , and Δ tmpA mutants were not rescued by the cfwA -dependent compounds identified here. However, a cfwA2 mutation enhanced the sporulation defects of both Δ tmpA and Δ fluG single mutants, suggesting that unidentified CfwA-dependent PKSs and/or NRPSs are involved in the production of hitherto-unknown compounds required for sporulation. Our results expand the number of known and predicted secondary metabolites requiring CfwA/NpgA for their biosynthesis and, together with the phylogenetic analysis of fungal PPTases, suggest that a single PPTase is responsible for the activation of all PKSs and NRPSs in A. nidulans .

In our search for quorum-sensing (QS) disrupting molecules, 75 fungal isolates were recovered from reef organisms (endophytes), saline lakes and mangrove rhizosphere. Their QS inhibitory activity was evaluated in Chromobacterium violaceum CVO26. Four strains of endophytic fungi stood out for their potent activity at concentrations from 500 to 50 μg mL⁻¹. The molecular characterization, based on the internal transcribed spacer (ITS) region sequences (ITS1, 5.8S and ITS2) between the rRNA of 18S and 28S, identified these strains as belonging to four genera: Sarocladium (LAEE06), Fusarium (LAEE13), Epicoccum (LAEE14), and Khuskia (LAEE21). Interestingly, three came from coral species and two of them came from the same organism, the coral Diploria strigosa. Metabolic profiles obtained by Liquid Chromatography-High Resolution Mass Spectrometry (LC-HRMS) suggest that a combination of fungal secondary metabolites and fatty acids could be the responsible for the observed activities. The LC-HRMS analysis also revealed the presence of potentially new secondary metabolites. This is, to the best of our knowledge, the first report of QS inhibition by marine endophytic fungi.

Ergosterol is an important component of fungal membranes. This sterol can be easily transformed to peroxide of ergosterol by photo-oxidation with singlet oxygen. Cultures of Papalauspora immersa were grown on Czapeck agar medium, and subjected to the following conditions: 1) irradiation with daylight and quartz light (excluding UV light), 2) addition by diffusion of yellowish eosine (0.1 mg/mL), and 3) the control (no yellowish eosine, under darkness conditions). Fungal growth was completely inhibited after the treatment with quartz light (3 h) and yellow eosine, and no growth was observed in subsequent subcultures. These results suggested that plasma membrane components changed significantly by the transformation of ergosterol to peroxide of ergosterol leading to fungal death. To confirm this, a second experiment on a larger scale was carried out in which the fungus was grown on liquid medium in test tubes, treated, irradiated, and tested for peroxide of ergosterol by ¹HNMR. This peroxide was only found in treated samples. These findings represent a new strategy for developing antifungal agents, based on ergosterol photo-oxidation which might probably be related to the disruption of the plasma membrane, instead of only preventing the ergosterol biosynthesis. The potential application of this strategy for the selective control or prevention of pathogenic fungi is considerable.