Diversity of endophytic fungi from the root bark of Syzygium zeylanicum, and the antibacterial activity of fungal extracts, and secondary metabolite

Abstract

The decoction of the root bark of Syzygium zeylanicum has been used as traditional medicine, such as for treating pathogenic bacterial infections. Endophytic fungi that live in medicinal plant tissues have a high species diversity and biological activities correlate with their host. Therefore, this study aimed to explore the diversity of endophytic fungi from the root bark of S. zeylanicum and to determine the antibacterial activity of endophytic fungi and their secondary metabolites. In this study, we isolate and identify the endophytic fungi from the root bark of S. zeylanicum, continued by screening their antibacterial activity against two Gram-negative bacteria (Escherichia coli InaCCB5 and Salmonella thypi ATCC1048 and two Gram-positive bacteria (Staphylococcus aureus InaCCB4 and Bacillus subtilis InaCCB1204) by the Kirby-Bauer method. The fungal extract with the highest antibacterial activity proceeded with the isolation and determination of the structure of their bioactive compounds. The isolates were morphologically identified. Isolates that showed strong antibacterial activity were identified by molecular identification. Isolation of bioactive compounds was carried out by chromatographic techniques and the determination of the structure of pure chemical compounds was performed by the spectroscopic analysis. In total, there were 8 isolates of endophytic fungi were obtained from the root bark of S. zeylanicum, namely SZR1 – SZR8. SZR2 isolate has the highest antibacterial activity. Molecular identification through phylogenetic analysis showed that SZR2 isolate had high similarity with Penicillium brefeldianum. Isolation of bioactive compounds from SZR2 produced compound 1 in the form of light yellow crystals which showed strong antibacterial activity against S. typhi, E. coli, and B. subtilis with MIC values of 64 g/mL. Compound 1 was identified as p-hydroxybenzaldehyde, which was also obtained in its host. In conclusion, the endophytic fungus Penicillium brefeldianum produces similar secondary metabolites and antibacterial activity as its host plant.