Abstract
We report the first secondary metabolite, 8,8′-bijuglone, obtained from pure cultures of the slow growing Douglas fir- (Pseudotsuga menziesii var. menziesii) foliage-associated fungus Zasmidium pseudotsugae. The quinone was characterized using extensive LC/MS and NMR-based spectroscopic methods. 8,8′-Bijuglone exhibited moderate antibiotic activity against Gram-positive pathogens and weak cytotoxic activity in the NCI-60 cell line panel and in our in-house human colon carcinoma (HCT-116) cell line. An analysis of the fungal genome sequence to assess its metabolic potential was implemented using the bioinformatic tool antiSMASH. In total, 36 putative biosynthetic gene clusters were found with a majority encoding for polyketides (17), followed by non-ribosomal peptides (14), terpenes (2), ribosomal peptides (1), and compounds with mixed biosynthetic origin (2). This study demonstrates that foliage associated fungi of conifers produce antimicrobial metabolites and suggests this guild of fungi may present a rich source of novel molecules.
Highlights
The foliar fungal microbiome of Douglas-fir evergreen trees (Pseudotsuga menziesii var. menziesii) is a complex and diverse microbial ecosystem with underexplored chemical ecology [1,2]
Zasmidium pseudotsugae isolated from the needles of P. menziesii var. menziesii was grown on 2%
Zasmidium pseudotsugae isolated from needles of P. menziesii var. menziesii was grownfrom on 2%
Summary
The foliar fungal microbiome of Douglas-fir evergreen trees (Pseudotsuga menziesii var. menziesii) is a complex and diverse microbial ecosystem with underexplored chemical ecology [1,2]. Douglas-fir is an important commercial conifer species in forest plantations for timber and most commonly used for Christmas trees in western North America, Europe, Australia, and New Zealand [3,4] Fungal pathogens, such as Nothophaeocryptopus gaeumannii, the causative agent of Swiss needle cast, have become a serious problem in Douglas-fir populations of western North America, where it has negatively affected the growth and production of this native conifer [2,4,5,6,7,8]. We focused on the Douglas-fir associated fungus Zasmidium pseudotsugae and its specialized metabolism. The quinone was characterized by a combination of LC/MS and oneand two-dimensional NMR techniques and assessed for its antimicrobial and cytotoxicity activity To our knowledge, this is the first bioactive metabolite isolated from Z. pseudotsugae
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