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

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.

Evaluation of the Antibacterial Activity of Crude Extracts Obtained From Cultivation of Native Endophytic Fungi Belonging to a Tropical Montane Rainforest in Colombia

“…Among all the evaluated strains, D. endophytica exhibited a color transition during the fermentation time, which corresponded to its ECE's potent bioactivity, resulting in an organic extract with the highest potential obtained during the primary screening. In addition, even when the evaluated mycelial organic crude extracts were found bioactive only against the Gram-positive pathogen, it is noting that the obtained extraction yields are within the range of obtained values for the solid fermentation of endolichenic fungi on rice media, where also Xylariaceae species presented the highest extraction yields (Santiago et al, 2021).…”

“…The presented study also emphasizes on the crucial role of systematical screening platforms in the rapid and effective prioritization of antimicrobial agents prior to chemical investigation of bioactive molecules. In some cases, the cost and investing time associated to the identification of new antimicrobial compounds could be avoid by the screening of microorganisms, which are previously known to produce specific potential antimicrobial agents into crude extracts (Caicedo et al, 2011;Santiago et al, 2021). Nonetheless, our results provide an initial step toward bioprospecting the Colombian southwestern endophyte diversity and highlight the value of preserving the native habitats owing to their promising ecosystemic applications in the biotechnological and pharmaceutical industries.…”

In pursuit of promising microbes for drug discovery: tapping endolichenic fungi (ELF) from lichens

“…It is, thus, possible that ELF protects the host against harmful conditions through the production of reactive oxygen species (ROS). Furthermore, Santiago and colleagues [37] recently reported that ELF metabolites may have protected the lichen from other possible harmful or invading microorganisms. Such assumption resulted from the metabolomics analyses of lichen hosts and their associated ELF, where a distinction between lichen and ELF metabolic profiles was observed.…”

Untargeted and Targeted LC-MS/MS Based Metabolomics Study on In Vitro Culture of Phaeoacremonium Species

“…In particular, enormous progress in LC-MS-based metabolomics has been made, providing researchers with a variety of chromatographic separation, ionization, and mass analysers [38,39]. Moreover, it has also been applied in the dereplication of already known substances in the early stages of the screening process of bioactive mixtures [40][41][42].…”