Isolation, purification, and structural identification of a new bacteriocin made by Lactobacillus plantarum found in conventional kombucha

In recent years, the demand for natural products has increased, as customers prefer this type of product over those with added chemical preservatives. The critical issues associated with natural products are how to maintain their safety and quality as well as how to prolong their shelf life. In this study, Lactobacillus plantarum SLG10, isolated from kombucha (a traditional fermented drink in South China), produced a novel bacteriocin, SLG10, which was found to exert antibacterial activity on both Gram-positive and Gram-negative bacteria, including multidrug-resistant strains. An innovative method, biochromatography coupled with reversed-phase high-performance liquid chromatography (RP-HPLC), was developed for the efficient screening and purification of the bacteriocin found in the cell-free suspension of L. plantarum SLG10. According to matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS), the isolated bacteriocin had a molecular mass of 1422 Da. The amino acid sequence was Asn-Ile-Val-Trp-Ghi-Leu-Ile-Gly-Leu-Pro-Ala-Gln-Al, as determined by N-sequencing. Bacteriocin SLG10 showed thermostability and pH tolerant characteristics and was sensitive to most proteases but not trypsin or pepsin. A well-defined linear conformation was suggested by circular dichroism (CD) spectroscopy and 3D structure predictions. The time-kill kinetics curve indicated that bacteriocin SLG10 was bactericidal. The antibacterial mechanism investigation revealed that bacteriocin SLG10 increased cell membrane permeability, causing potassium ion release. We also found that bacteriocin SLG10 can inhibit the formation of biofilms. These results suggest that bacteriocin SLG10 has a potential application in the food industry.