Bacterial Strains and Culture Conditions

Lactococcus lactis subsp. lactis LDTM6802 (KCTC18611P) and Lactococcus lactis subsp. cremoris LDTM6803 (KCTC18612P) were isolated from cucumber kimchi and raw milk products from Gangwon Province, South Korea. Collected kimchi samples were serially diluted 10-fold using 0.85% NaCl solution (Sigma-Aldrich, USA) and homogenized. Serial dilutions were plated on M17 (Difco, USA) supplemented with 0.5% lactose (GM17) (Difco) agar for lactococci isolation. Inoculated plates were incubated at 30°C under aerobic conditions for 48 h. The strains were deposited in the Korean Collection for Type Cultures (KCTC). We used the commercial starter culture CHN-11 (Chr. Hansen, Denmark), which contains Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. lactis biovar diacetylactis, and Leuconostoc subsp. mesenteroides. We isolated Lactococcus lactis subsp. cremoris (CHN-11-3), Lactococcus lactis subsp. lactis biovar diacetylactis (CHN- 11-1), and Leuconostoc subsp. mesenteroides (CHN-11-48) from CHN-11 starter, as confirmed by 16S rRNA gene sequence analysis. Lactococcus lactis subsp. lactis IL1403 (KCTC3115) was used as a type strain. These strains were cultured in M17 (Difco) supplemented with 0.5% lactose (GM17) at 30°C under aerobic conditions and stored in 20% glycerol (Sigma-Aldrich) at -80°C.