Streptomycetes as a promising source of antimicrobial compounds: A GC-MS-based dereplication study

The extensive microbial resistance to existing antimicrobial medicines presents a significant issue in treating diverse microbial infections, whereas actinomycetes remain a viable source of antimicrobial natural products. We planned to employ gas chromatography-mass spectrometry (GC-MS)-based dereplication analysis to investigate the chemical profile of a bioactive actinomycete. Our actinomycete MFS-I31 demonstrated broad antimicrobial potential against the bacterial pathogens Staphylococcus aureus (ATCC 43300), Listeria monocytogenes (ATCC 7644), Escherichia coli (ATCC 25922), and Salmonella enterica (ATCC 14028), as well as the yeast-like fungus Candida albicans (ATCC 60193). The 16S rRNA gene sequencing of the MFS-I31 isolate exhibited a powerful resemblance to Streptomyces species. The characterization of the major antibacterial compounds in its cell-free supernatant (CFS) revealed good stability at different temperatures ranging from 4 °C to 93 °C, whereas the activity was diminished upon precipitation using ammonium sulphate indicating the proteinaceous nature of the major antimicrobial compounds. Notably, the proton nuclear magnetic resonance (¹H NMR) revealed peaks in both aromatic and aliphatic areas, demonstrating the variety of the principal secondary metabolites in the crude extract of Streptomyces sp. MFS-I31. Moreover, the GC-MS-based dereplication research of our actinomycete revealed the richness of its chemical profile with different classes of compounds, including volatile molecules with antimicrobial properties. Finally, the contact bioautography demonstrated the good chance of isolating antimicrobial natural products from Streptomyces sp. MFS-I31 if it would be subjected to chemical isolation work. To summarize, soil Streptomycetes remain a valuable source of many antimicrobial natural compounds, particularly when implementing chemical profiling and dereplication studies.