Secondary Metabolites of the Zoanthid-Derived Fungus Trichoderma sp. TA26-28 Collected from the South China Sea

Abstract

Marine microorganisms, particularly marine-derived fungi, have been recognized as a potential source of structurally novel and biologically potent metabolites that have become significant chemical entities for drug discovery [1]. Recently, a growing number of fungi derived from marine invertebrates have been reported to produce novel bioactive secondary metabolites [2]. However, chemical studies on fungi derived from zoanthids are relatively rare [3–6]. As part of our ongoing investigation on natural bioactive products from marine fungi in the South China Sea, a zoanthid-derived fungus, authenticated as Trichoderma sp. TA26-28, attracted our attention because the EtOAc extract of the fungal fermentation broth exhibited significant antibacterial activity against a panel of pathogenic bacteria. Chemical investigation of the extract led to the isolation of eight known compounds, including three anthraquinones 1–3, one xanthone 4, one epoxy-lactone 5, and three cerebrosides 6–8. We report herein the fermentation, isolation, structure elucidation, and biological activity of these metabolites. Fungus Material. The fungal strain Trichoderma sp. (TA26-28) was isolated from a piece of fresh tissue from the inner part of the zoanthid Palythoa haddoni (GX-WZ-20100026), collected from the Weizhou coral reef in the South China Sea in April 2010. The fungus was identified as a Trichoderma sp. based on sequence analysis of the internal transcribed spacer, and its sequence data had been submitted to GenBank, accession number JF819149. The strain was deposited at the Key Laboratory of Marine Drugs, the Ministry of Education of China, School of Medicine and Pharmacy, Ocean University of China, Qingdao, P. R. China. Culture Conditions. Starter cultures were maintained on GPY medium (glucose 20 g, peptone 10 g, yeast extract 10 g, agar 20 g in 1 L artificial seawater). Plugs of agar supporting mycelia growth were cut and transferred aseptically to a 250 mL Erlenmeyer flask containing 100 mL of liquid medium (composition of medium: 200 g/L cooked and sliced potatoes, 20 g/L glucose in 1 L artificial seawater). The flask was incubated at 27 C on a rotary shaker for one week. The mycelium was aseptically transferred to 1 L Erlenmeyer flasks containing culture liquid (400 mL). The flasks were then incubated at 27 C without shaking for 4 weeks.