Glycinocins E-H, Antimicrobial Lipopeptides Produced by a Streptomyces Strain

In an antifungal screening of extracts from microbial strains isolated from gypsum outcrops in Granada, Spain, four new cyclic lipopeptides, glycinocins E-H (1-4), were identified from Streptomyces sp. CA-297274 and exhibited potent activity against Zymoseptoria tritici, the causal agent of septoria tritici blotch of wheat. Isolation and structure elucidation performed using HR-MS/MS, 1D and 2D NMR, and Marfey's analyses, revealed that structures contained an Asp-Gly-Asp-Gly motif in the peptide scaffold, typical of calcium-dependent antibiotics. Genome sequencing and bioinformatic analysis of the strain uncovered a biosynthetic gene cluster consistent with the production of these compounds and helped to correct the absolute configuration determined by Marfey's analysis of some amino acid residues. The isolated metabolites displayed notable antifungal activity against Z. tritici, with minimum inhibitory concentration values in the micromolar range (Compound 4, 9.5 μM), and calcium-dependent antibacterial activity against methicillin-resistant Staphylococcus aureus (5.2 μM for 4) and vancomycin-resistant Enterococcus faecium (3.0 μM for 4), as anticipated by their structural analysis. Glycinocins E-H displayed no cytotoxicity against the human liver cancer cell line HepG2. These findings expand the chemical diversity of calcium-dependent antibiotics and highlight the ecological and therapeutic potential of extremophile-derived actinomycetes as a source of novel bioactive compounds.