Characterization of bacteriocin ST8KF produced by a kefir isolate Lactobacillus plantarum ST8KF

Lactobacillus plantarum ST8KF, isolated from kefir, produced a 3.5 kDa bacteriocin (bacST8KF) active against Lb. casei, Lb. salivarius, Lb. curvatus and Listeria innocua. BacST8KF was sensitive to proteolytic enzymes, but stable between pH 2.0 and 10.0, and heat resistant (20 min at 121 °C). BacST8KF did not adsorb to the surface of the producer cell. Maximum activity (25,600 AU mL−1) was recorded in MRS broth with glucose, in MRS broth with glucose replaced by sucrose, and in MRS broth with glucose, supplemented with KH2PO4 after 24 h at 30 °C. Tri-ammonium citrate and glycerol in excess of 5.0 g L−1 repressed bacST8KF production. Production of bacST8KF increased from 800 AU mL−1 after 3 h of fermentation in MRS broth at 30 °C to 12,800 AU mL−1 after 9 h and to 51,200 AU mL−1 after 27 h. These results suggest that bacST8KF may be a secondary metabolite and shows that its mode of activity is bacteriostatic.