Secondary metabolites of a marine-derived Penicillium ochrochloron

Peter M Eze,Charles O Esimone,Festus B C Okoye,Yang Liu,Ying Gao,Lasse Van Geelen,Chika P Ejikeugwu,Rainer Kalscheuer,Peter Proksch

doi:10.15835/nsb13311020

Abstract

Extremophilic fungi have received considerable attention recently as new promising sources of biologically active compounds with potential pharmaceutical applications. This study investigated the secondary metabolites of a marine-derived Penicillium ochrochloron isolated from underwater sea sand collected from the North Sea in St. Peter-Ording, Germany. Standard techniques were used for fungal isolation, taxonomic identification, fermentation, extraction, and isolation of fungal secondary metabolites. Chromatographic separation and spectroscopic analyses of the fungal secondary metabolites yielded eight compounds: talumarin A (1), aspergillumarin A (2), andrastin A (3), clavatol (4), 3-acetylphenol (5), methyl 2,5-dihydro-4-hydroxy-5-oxo-3-phenyl-2-furanpropanoate (6), emodin (7) and 2-chloroemodin (8). After co-cultivation with Bacillus subtilis, the fungus was induced to express (-)-striatisporolide A (9). Compound 1 was evaluated for antibacterial activity against Staphylococcus aureus, Acinetobacter baumannii, Mycobacterium smegmatis, and M. tuberculosis, as well as cytotoxicity against THP-1 cells. The compound, however, was not cytotoxic to THP-1 cells and had no antibacterial activity against the microorganisms tested. The compounds isolated from P. ochrochloron in this study are well-known compounds with a wide range of beneficial biological properties that can be explored for pharmaceutical, agricultural, or industrial applications. This study highlights the bioprospecting potential of marine fungi and confirms co-cultivation as a useful strategy for the discovery of new natural products.

Highlights

The frequent re-isolation of known metabolites from fungi has turned the interest of natural products chemists to hitherto less investigated ecological niches such as arctic glaciers, deep-sea hydrothermal vents or hypersaline lakes (Wilson and Brimble, 2009; Liu et al, 2016)
One of the fungi was identified as Penicillium ochrochloron according to the molecular identification protocol of DNA amplification and sequencing of the internal transcribed spacer (ITS) region previously described (Kjer et al, 2010)
Co-culture of P. ochrochloron with B. subtilis resulted in the expression of compound 9 previously undetected in extract of the fungal axenic culture

Summary

Introduction

The frequent re-isolation of known metabolites from fungi has turned the interest of natural products chemists to hitherto less investigated ecological niches such as arctic glaciers, deep-sea hydrothermal vents or hypersaline lakes (Wilson and Brimble, 2009; Liu et al, 2016). Fungi that live at elevated temperature, acidic or alkaline pH, high pressure, high salt concentration and /or low nutrient concentrations are called extremophiles. These fungi have developed unique metabolic mechanisms to produce bioactive secondary metabolites as a response to environmental stress (Satyanarayana et al, 2005; Ma et al, 2010). When compared to the thousands of fungal species known from terrestrial environments, only a few have been described for oceans and estuaries which represent the largest part of the earth's surface Some of these fungi, may occur in both seawater and freshwater or terrestrial habitats (Jones, 2000; Gomes et al, 2008)

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