Abstract
Natural products with novel chemistry are urgently needed to battle the continued increase in microbial drug resistance. Mushroom-forming fungi are underutilized as a source of novel antibiotics in the literature due to their challenging culture preparation and genetic intractability. However, modern fungal molecular and synthetic biology tools have renewed interest in exploring mushroom fungi for novel therapeutic agents. The aims of this study were to investigate the secondary metabolites of nine basidiomycetes, screen their biological and chemical properties, and then investigate the genetic pathways associated with their production. Of the nine fungi selected, Hypholoma fasciculare was revealed to be a highly active antagonistic species, with antimicrobial activity against three different microorganisms: Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae. Genomic comparisons and chromatographic studies were employed to characterize more than 15 biosynthetic gene clusters and resulted in the identification of 3,5-dichloromethoxy benzoic acid as a potential antibacterial compound. The biosynthetic gene cluster for this product is also predicted. This study reinforces the potential of mushroom-forming fungi as an underexplored reservoir of bioactive natural products. Access to genomic data, and chemical-based frameworks, will assist the development and application of novel molecules with applications in both the pharmaceutical and agrochemical industries.
Highlights
Mushroom-forming fungi are recognized for producing a plethora of chemical compounds to help defeat competitive organisms that coexist in their ecosystem (Schmidt-Dannert, 2016)
The chemical extracts were separately spotted on the thin-layer chromatography (TLC) plates and developed in different solvent systems—nonpolar, polar, and semi-polar—which were tested against Bacillus subtilis
Following 2 weeks of incubation at 25◦C, the colony diameters were measured, and the results indicated potential successful gene silencing in transformant Hfas-asTR14, whereby silenced colonies demonstrated a slower rate of growth and different form of mycelia compared to the wild type (Figure 7B)
Summary
Mushroom-forming fungi are recognized for producing a plethora of chemical compounds to help defeat competitive organisms that coexist in their ecosystem (Schmidt-Dannert, 2016) These are specialized secondary metabolites (SMs) or natural products, which are known for their wideranging useful biological activities including antimicrobial, antitumor, and insecticide properties (Wilkins and Harris, 1944; Wilkins, 1946; de Mattos-Shipley et al, 2016). Basidiomycetes are known to produce mycotoxins with significant biological activities with both medicinal and agricultural applications, for example psilocybin from Psilocybe spp., strobilurin from Strobilurus tenacellus, and pleuromutilin from Clitopilus passeckerianus (Bailey et al, 2016; Nofiani et al, 2018; Fricke et al, 2019), the main groups of natural products that have been isolated from basidiomycetes fungi are typically halogenated compounds and terpenoids. These include tetrachlorinated phenols, illudanes, sterpurenes, and illudalanes, all of which are largely produced exclusively by fungi, with one exception being illudalanes, which are produced by some plants (De Jong and Field, 1997; Quin et al, 2014)
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