Abstract
A lytic bacteriophage fTFF221, specific for nisin-producing Lactococcus lactis subsp.lactis TFF221, was first isolated from kung-jom, a Thai traditional fermented shrimp paste. The plaques were clear and round-shaped on the lawn of bacteria, indicating its lytic activity. Restriction analysis indicated that genome of phage fTFF221 was double-stranded DNA. Transmission electron microscopy revealed that it had an icosahedral head with a contractile tail and a baseplate, and might be tentatively classified as a member of the Myoviridae family. Structural protein profile of phage fTFF221 by SDS-PAGE showed five bands with molecular masses estimated at, 45.3, 39.8, 26.8, 16.5, and 8.9 kDa. One-step growth experiment of its lytic activity appeared latent, and burst periods of 30 and 120 min, respectively, with a burst size of about 60 PFU/infected cell. The phage was highly specific to its host. None of the tested LAB strains was sensitive to phagefTFF221. Phage was stable over a wide pH range of 4 to 10 at 30°C for 1 h, and survived after heating at 70°C for at least 3 min. Phage had more survivals in 1 to 5% of NaCl than in 10% of NaCl. Kinetic monitoring of L. lactis subsp. lactis TFF221-GFP+ starter, which was containing pN014-GFP and had a fluorescent ability, and phage fTFF221 in food model, demonstrated the considerable decrease in the number of the starter in the presence of phage. Knowledge of these basic properties of this phage might be important for the development of using starter fermentation. Key words: Bacteriophage, fermented food, Lactococcus lactis.
Highlights
Lactic acid bacteria (LAB) are commonly used as starter cultures in the production of a great multitude of fermented foods (Caplice and Fitzgerald, 1999)
30 Thai fermented food samples were examined for phages against nisin-producing L. lactis subsp. lactis TFF221 strain (Table 2)
These samples were screened for the presence of phages by spot test using L. lactis subsp. lactis TFF221 as an indicator host cell
Summary
Lactic acid bacteria (LAB) are commonly used as starter cultures in the production of a great multitude of fermented foods (Caplice and Fitzgerald, 1999) These organisms are able to produce a wide variety of antimicrobial compounds, including proteinaceous substances called bacteriocins (Leroy and de Vuyst, 2004). Lactis TFF221, which is nisin-producing, has been isolated from kungjom, a Thai traditional fermented shrimp paste (Rattanachaikunsopon and Phumkhachorn, 2008). It has been developed for use as a functional starter culture in order to obtain products with high quality, consistency and safety from some serious food pathogens. The problem has stimulated researchers and manufacturers to continually devise innovative and effective procedures
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