Biodiscovery of Potential Antibacterial Diagnostic Metabolites from the Endolichenic Fungus Xylaria venustula Using LC-MS-Based Metabolomics.

Krystle Angelique A Santiago,Adeline Su Yien Ting,Yuen Lin Cheow,Thomas Edison E Dela Cruz,Ruangelie Edrada-Ebel

doi:10.3390/biology10030191

Krystle Angelique A Santiago, Adeline Su Yien Ting + Show 3 more

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https://doi.org/10.3390/biology10030191

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Abstract

Three species of the lichen Usnea (U. baileyi (Stirt.) Zahlbr., U. bismolliuscula Zahlbr. and U. pectinata Stirt.) and nine associated endolichenic fungi (ELF) were evaluated using a metabolomics approach. All investigated lichen crude extracts afforded antibacterial activity against Staphylococcus aureus (minimum inhibitory concentration (MIC): 0.0625 mg/mL), but none was observed against Escherichia coli, while the ELF extract Xylaria venustula was found to be the most active against S. aureus (MIC: 2.5 mg/mL) and E. coli (MIC: 5 mg/mL). X. venustula was fractionated and tested for to determine its antibacterial activity. Fractions XvFr1 to 5 displayed bioactivities against both test bacteria. Selected crude extracts and fractions were subjected to metabolomics analyses using high-resolution LC-MS. Multivariate analyses showed the presence of five secondary metabolites unique to bioactive fractions XvFr1 to 3, which were identified as responsible for the antibacterial activity of X. venustula. The p-values of these metabolites were at the margin of significance level, with methyl xylariate C (P_60) being the most significant. However, their high variable importance of projection (VIP) scores (>5) suggest these metabolites are potential diagnostic metabolites for X. venustula for "dual" bioactivity against S. aureus and E. coli. The statistical models also showed the distinctiveness of metabolites produced by lichens and ELF, thus supporting our hypotheses of ELF functionality similar to plant endophytes.

Highlights

As symbiotic organisms, lichens are known as unique sources of bioactive secondary metabolites called lichen substances [1]
Lichen crude extracts only showed inhibition against S. aureus, with U. bismolliuscula collected from the Philippines (PH) showing the highest ZOI followed by U. baileyi (PH)
Six of the nine endolichenic fungi (ELF) crude extracts were active against S. aureus and E. coli, with Annulohypoxylon albidiscum and Xylaria venustula exhibiting the strongest activities against S. aureus, albeit having a high minimum inhibitory concentrations (MICs) value of

Summary

Introduction

Lichens are known as unique sources of bioactive secondary metabolites called lichen substances [1]. Of the lichen, is reported to produce approximately 1000 chemically diverse lichen substances [2] Most of these metabolites are unique to lichens, with only a small portion occurring in fungi and higher plants [3]. These substances were found to exhibit significant biological activities including antibacterial [4], antifungal [5], anti-inflammatory [6], antioxidant [7], antiviral [8] and cytotoxic [9] activities. A group of asymptomatic fungi that resemble plant endophytes was discovered thriving inside healthy lichen thalli [11,12] This group of fungi, known as endolichenic fungi (ELF), was first described in 1990 [13]. ELF are known to possess secondary metabolites that are hypothesized to be distinct from those produced by lichens [17]

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