Phenyl Ethers from the Marine-Derived Fungus Aspergillus tabacinus and Their Antimicrobial Activity Against Plant Pathogenic Fungi and Bacteria

Marine fungi produce various secondary metabolites with unique chemical structures and diverse biological activities. In the continuing search for new antifungal agents from fungi isolated from marine environments, the culture filtrate of a fungus Aspergillus tabacinus SFC20160407-M11 exhibited the potential to control plant diseases caused by fungi. From the culture filtrate of A. tabacinus SFC20160407-M11, a total of seven compounds were isolated and identified by activity-guided column chromatography and spectroscopic analysis: violaceol I (1), violaceol II (2), diorcinol (3), versinol (4), orcinol (5), orsellinic acid (6), and sydowiol C (7). Based on in vitro bioassays against 17 plant pathogenic fungi and bacteria, violaceols and diorcinol (1-3) showed a broad spectrum of antimicrobial activity with minimum inhibitory concentration values in the range of 6.3-200 μg mL-1. These compounds also effectively reduced the development of rice blast, tomato late blight, and pepper anthracnose caused by plant pathogenic fungi in a dose-dependent manner. Our results suggest that A. tabacinus SFC20160407-M11 and its phenyl ether compounds could be used for developing new antimicrobial agents to protect crops from plant pathogens.