Chemical mycology of freshwater ascomycetes from North Carolina, USA

During our ongoing chemical mycological investigations of freshwater fungi in North Carolina, USA, we found two Dothideomycetes taxa from freshwater habitats in the Piedmont region that shared morphological similarities with species of Minutisphaera. These new collections prompted a chemical study of the secondary metabolites produced by this genus as well as a molecular phylogenetic study of relationships of taxa within Minutisphaera. Based on maximum likelihood and Bayesian analyses of molecular data, as well as examination of morphology, we describe and illustrate two new species of Minutisphaera. Chemical analysis of the organic extract M. aspera sp. nov. resulted in the isolation and characterization of five known secondary metabolites, of which four were dipeptides (1 – 4) and one was an aromatic polyketide (5). On the other hand, two aromatic polyketides (5 and 6) were isolated and identified from the organic extract of M. parafimbriatispora sp. nov. The isolated compounds were tested for their antimicrobial activity against an array of bacteria and fungi. Compound 6 showed promising activity against Staphylococcus aureus and Mycobacterium smegmatis with MIC values of 30 and 60 µg/mL, respectively. The Minutisphaera clade did not share phylogenetic affinities with any existing taxonomic group within the Dothideomycetes. We therefore establish a new order, Minutisphaerales, and new family, Minutisphaeraceae, for this monophyletic clade of freshwater ascomycetes.