Diversity and Antibacterial Activity of Fungus–Bacterium Symbionts from Marine Sediments in the Beibu Gulf

The fungus-bacterium symbionts are widespread in nature, but the interaction of these organisms from marine origins remain poorly understood. In this study, we investigated the diversity and antibacterial activity of marine fungus-bacterium symbionts isolated and purified from the 14 marine sediments collected of the Beibu Gulf, China. A total of 41 fungus-bacterium symbionts, belonging to 2 phyla, 8 orders, 16 families and 18 genera were obtained. By comparing the isolation frequency values, Trichoderma (19.51%) and Fusarium (14.63%) were found to be the most commonly occurring genera. The antibacterial activity of these 41 marine fungus-bacterium symbionts was evaluated using a dual culture method aganist Klebsiella pneumoniae, Acinetobacter baumannii, Staphylococcus epidermidis, Micrococcus luteus, and methicillin-resistant Staphylococcus aureus. Nineteen active symbionts were indentified, accounting for 46.3% of the total number of fungi tested. Through SYTO9 staining and transmission electron microscopy analysis, we confirmed that the colonizing location of GXIMD04141 (a symbiotic bacterium) was within its host fungus. Our findings suggest that marine fungus-bacterium symbionts have abundant diversity and strong antibacterial activity in the Beibu Gulf.