Metabolites from Lactococcus lactis subsp. lactis : Isolation, Structure Elucidation, and Antimicrobial Activity.

Herein, we disclose the identification of novel metabolites from a potential probiotic strain, Lactococcus lactis subsp. lactis, obtained from traditional dairy milk samples collected in Maharashtra, India (in January 2021). Isolated metabolites include pyrazin-2-carboxamide [ 1 , pyrazinamide, a potential antitubercular drug], 3,5-dihydroxy-6-methyl-2,3-dihydro-4 H -pyran-4-one ( 2 , DDMP), 2,4-di- tert -butylphenol ( 3 ), and hexadecanoic acid ( 4 , palmitic acid). The chemical structures of these metabolites were elucidated through extensive 1D NMR ( 1 H and 13 C) and 2D NMR (HSQC, HMBC, and NOESY) analyses, high-resolution mass spectrometry, high-performance liquid chromatography, and single-crystal X-ray crystallography. Furthermore, these novel metabolites exhibited potent inhibitory activities against various bacteria, fungi, and yeast strains with minimum inhibitory concentrations ranging between 1.56 and 25 μg/mL, and compounds 1 and 3 were found to be most active against a wide range of microbial strains tested.