Potential aquaculture probiont Lactococcus lactis TW34 produces nisin Z and inhibits the fish pathogen Lactococcus garvieae

Abstract

Bacteriocin-producing Lactococcus lactis TW34 was isolated from marine fsh. TW34 bacteriocin inhibited the growth of the fsh pathogen Lactococcus garvieae at 5 AU/ml (minimum inhibitory concentration), whereas the minimum bactericidal concentration was 10 AU/ml. Addition of TW34 bacteriocin to L. garvieae cultures resulted in a decrease of six orders of magnitude of viable cells counts demonstrating a bactericidal mode of action. The direct detection of the bacteriocin activity by Tricine-SDS-PAGE showed an active peptide with a molec- ular mass ca. 4.5 kDa. The analysis by MALDI-TOF-MS detected a strong signal at m/z 2,351.2 that corresponded to the nisin leader peptide mass without the initiating methio- nine, whose sequence STKDFNLDLVSVSKKDSGASPR was confrmed by MS/MS. Sequence analysis of nisin structural gene confrmed that L. lactis TW34 was a nisin Z producer. This nisin Z-producing strain with probiotic properties might be considered as an alternative in the pre- vention of lactococcosis, a global disease in aquaculture systems.