Incidence of Lysogeny in Wild Lactococcal Strains

¹ Instituto de Productos Lácteos de Asturias (IPLA), Consejo Superior de lnvestigaciones Cientificas (CSIC), Apdo. de Correos 85 33300-Villaviciosa, Asturias, Spain

The incidence of lysogeny among 172 lactococcal strains, isolated from natural dairy fermentations and selected by their high capacity to coagulate milk and to produce lactic acid, was studied. Lysis of 92 strains (53% of the strains tested) was observed after using mitomycin C for induction of cultures. Fifty-one of these 92 strains released phages that were able to propagate on indicator strains. Twenty-eight (16%) of the 172 strains tested acted as host for at least one phage, although some supported the development of more than one phage isolate. Spontaneous induction was insignificant in >50% of strains inducible by mitomycin C, but titers after mitomycin C induction varied between 10¹ and l0⁶ pfu/ml. No plaque formation was observed at 37°C. The bacteriophages belonged to the family Siphoviridae, as revealed by electron microscopy. Head and tail dimensions ranged widely. Some temperate phages that were unable to form plaques of lysis appeared to be defective viral particles.

Key Words: lysogeny • lactococci • farmhouse cheese

Submitted on June 16, 1994
Accepted on December 19, 1994

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