Antibacterial metabolites from Australian macrofungi from the genus Cortinarius

Abstract

Mushrooms have demonstrated significant pharmacological activity including antimicrobial, cytotoxic, anti-inflammatory, hypoglycaemic, immunomodulatory and hallucinogenic properties [1]. The fungi of Australia are diverse, largely endemic and, in contrast to their floral counterparts, have not undergone intensive taxonomic, chemical or pharmacological evaluation [2]. Furthermore, some Australian indigenous macrofungi are currently considered to be conspecific with Northern Hemisphere species, might be described as separate species once taxonomic revisions are carried out [3]. Consequently Australian mushrooms represent an under-explored resource of potentially novel metabolites. In this study, ethyl acetate and aqueous fractions from 117 collections of Australian macrofungi belonging to the genusCortinarius were screened for antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa. Overall, the lipophilic fractions were more active than the aqueous fractions. The ethyl acetate fractions of most or all collections of 13 described Cortinarius species and 47 collections of un-described Cortinarius species exhibited IC50 values of ≤0.09mg/mL against S. aureus. In contrast, most or all collections of only 4 described Cortinarius species and only 11 un-described Cortinarius collections exhibited similar effects against P. aeruginosa (IC50 ≤0.09mg/mL). The fungal octaketides austrocortilutein, austrocortirubin, torosachrysone, isolated from C. basirubescens, together with physcion and emodin were found to strongly inhibit the growth of S. aureus (IC50 0.7–12µg/mL) whereas only physcion and emodin exhibited potency against P. aeruginosa (IC50 1.5 and 2.0µg/mL, respectively) [4]. Australian mushrooms from the genus Cortinarius are promising sources of natural products for further drug development research, due to the high biological diversity and unique evolutionary lineages found only in the region. This is coupled with the large proportion of bioactive species and high diversity of chemical constituents.