LC-ESI-QTOF-HRMS-Based Myxobacterial Metabolite Profiling for Potential Anti-Breast Cancer Extracts

Members of Myxococcales have been known as slime bacteria, a unique microbiome in natural habitats with complex multicellular behaviour, sliding movement, and unusual fruiting body morphologies. According to previous reports, myxobacteria typically produced diverse families of secondary metabolites with various biological functions, including antimicrobial, antiviral, and antitumor properties. This study used an MTT cytotoxicity assay to evaluate total extracts from 43 myxobacterial strains on the MDA-MB-231 breast tumour cell line. Among these, one strain was determined to produce the highest anticancer activity with IC50 values of 6.25 ± 0.07 μg/mL, 3.9 times more than doxorubicin. Based on the morphological characteristics (colonies, vegetative cells, fruiting bodies, and myxospores) and 16S rDNA gene sequence, the potent strain was classified as belonging to the genus Myxococcus (Myxococcus stipitatus) named GL41 (Accession number ON076907). Then, profiling the ethyl acetate extract from the GL41 strain was performed to analyze the principle components using liquid chromatography coupled with electrospray ionization mass spectrometry (LC-ESI-QTOF-HRMS). As a result, 5 metabolite peaks were revealed based on the exact pseudomolecular ion [M+H]+ (exactly to 0.0001 m/z) and isotopic distributions. In addition, unknown compound peaks were predicted and exhibited as the putative molecular formulas, contributing to variation among the metabolite profiles under investigation. In conclusion, LC-HRMS-based metabolite screening is an effective and rapid identification approach for discovering potent candidates for subsequent characterization.