Diversity of fungal communities and changes in antibacterial activity of artificially culturable fungal secondary metabolites from diseased and healthy fruits of Cinnamomum burmannii

Abstract

Background Studies on the function of endophytic fungal communities in healthy plant tissues are not new, while little is known about the functional changes of fungal communities in pathogenic plant tissues. Healthy fruits of Cinnamomum burmannii are an important medicinal resource, infection by phytopathogenic fungi causes changes in volatile components, with the corresponding, the functional characteristics and potential value of fungal communities in diseased fruits have not been reported. Consequently, characterization in the composition structure and antibacterial activity of fungal communities from healthy and diseased fruits of C. burmannii was investigated, the secondary metabolites in the fungus Medicopsis romeroi were reported for the first time. Results The fungal community in diseased fruits differed from that of healthy fruits at the Phylum, Class, Order or Genus levels, with important changes in the species and relative abundance of the dominant flora. Forty-one different strains (11 from healthy fruits and 30 from diseased fruits) were successfully identified by morphological and molecular biological methods which were classified into 8 groups and 23 genera using phylogenetic tree analysis, with Pleosporales, Glomerellales and Hypocreales were the dominant group at the phylum level and Colletotrichum was the dominant group at the genus level. The secondary metabolites of all strains had different degrees of antibacterial activity, while the secondary metabolites of diseased fruit symbiotic fungi were generally stronger than those of healthy fruits, with the active secondary metabolites dominated by small and medium polar compounds. Both the up-regulated and down-regulated flora in diseased fruit had strong antibacterial activity. Two new compounds, 5, 6-Dimethoxy-[1',1:4,1''-terphenyl]-2-ol (1), 5-(methoxycarbonyl)-2-methylbenzo[d][1, 3]dioxole-2-carboxylic acid (2) and three known compounds (3, 4, 5) were isolated and identified for the first time from the symbiotic fungus Medicopsis romeroi. Conclusion Although the diversity of fungal communities decreases after plant fruit disease, the antibacterial activity capacity of the fungi among them is generally enhanced, and the development of secondary metabolites of active strains from diseased fruits holds great promise. This study is significant for understanding the functional variation of bioactivity in fungal communities and developing a broader range of bioactive resources.