Antifungal and new metabolites of Myrothecium sp Z16, a fungus associated with white croaker Argyrosomus argentatus

Aims: Fungal infection is still a life-threatening risk for the immunocompromised population such as AIDS patients and those who receive treatments with immunosuppressors and/or frequent administrations of wide-spectrum antibiotics, which inevitably lead to the drug resistance and unbalanced microflora populations. The present work was accordingly performed to characterize more potent antifungal metabolites from various cultures of marine fungi residing in white croaker Argyrosomus argentatus. Methods and Results: The three most common opportunistic human pathogens Candida albicans (CCCCM ID 00148), Aspergillus niger (CCCCM ACCC 30005) and Trichophyton rubrum (CCCCM ID 00001) were selected as test fungi. A total of 16 cultivable fungal strains were isolated from the variant tissues of Ar. argentatus collected from the Yellow Sea, followed by preliminary antifungal screenings of the EtOAc extracts of the corresponding cultures. As a result, the inhibition of the three target fungi, plus being allergic to isolators' skin, were discerned with the EtOAc extract of the fungus under the isolation number Z16 that was identified subsequently as Myrothecium sp. by a combination of morphological and 18S rDNA finger-typing characteristics. A follow-up bioassay fractionation of the EtOAc extract, in conjunction with spectral analyses [MS, H-1-NMR, C-13-NMR, distortionless enhancement by polarization transfer (DEPT), heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond resonance (HMBC)wherever required, afforded eventually the characterization of a new acid (compound 1: 4,5-ditridecyl-octanedioic acid), three macrocyclic trichothecenes including roridin A (compound 2), verrucarin A (compound 3) and 8 beta-acetoxy-roridin H (compound 4), (22E,24R)-cerevisterol (compound 5) and N-phenyl-beta-amino-naphthalene (compound 6). In vitro antifungal tests showed that the three trichothecenes were active against A. niger, T. rubrum and C. albicans with MICs of 31.25, 62.5 and 125 mu g ml(-1) for compound 2, 250, 125 and 31.25 mu g ml(-1) for compound 3 as well as 125, 62.5 and 125 mu g ml(-1) for compound 4 respectively. The MICs of ketoconazole (co-assayed herewith as a positive reference) against A. niger, T. rubrum and C. albicans were 31.25, 250, 31.25 mu g ml(-1) respectively. A preliminary structure-activity relationship of the antifungal trichothecenes was highlighted in brief. Conclusions: The present investigation demonstrated that marine fungus Myrothecium sp. Z16 associated with white croaker (Ar. argentatus), was an efficient producer of a new acid and antifungal trichothecenes, the latter presumably being also the allergic substances in the culture. Significance and Impact of the Study: The title marine fungus was investigated to be a resource of new aliphatic acid, and trichothecenes with potent antifungal and dermal toxic actions.