Five mutant of Lactococcus lactis subsp. cremoris 3107 resistant to phage TP901-1 were obtained after treatment with ethyl methanesulfonate. Two of the mutants were also resistant to phage fLC3. The remaining three mutants were as sensitive as 3107. Mutants E46 and E100 did not adsorb the two phages. Mutants E119, E121 and E126 adsorbed phage fLC3 as well as 3107 but phage TP901-1 with significantly reduced efficiency. All, except E46, could be lysogenized with phage TP901-BC1034, a derivative of TP901-1 harboring an erythromycin-resistance marker. However, the lysogenization frequency was 103-104 fold higher for 3107 than for the mutants. Mitomycin C induction of lysogenized mutants 3107 indicated that phage propagation was not affected in these four mutant. Electron microscopy and analysis of total DNA of infected cells showed that DNA was liberated from the phage particle during infection of strain 3107 with TP901-1 and that intracellular phage DNA replication occurred. This was not the case for mutants E121 and E126. This strongly suggests that some step starting with triggering DNA release and ending with DNA injection is impaired during infection with TP901-1. As such impairment was not seen when infection E-119, E121 and E126 with fLC3, we conclude that TP901-1 and fLC3 either are differently triggered by their receptor or utilize differenct pathways of injection.
Fems Microbiology Letters, 2007, Vol 276, Issue 2, p. 156-164