Microbiological and molecular impacts of AbiK on the lytic cycle of Lactococcus lactis phages of the 936 and P335 species.

The lactococcal abortive infection mechanism AbiK was previously shown to be highly effective against the small isometric-headed bacteriophage ul36 of the P335 species, as evidenced by an efficiency of plaquing (e.o.p.) of 10(-6), a 14-fold reduction in the burst size and an efficiency at which centres of infection form (e.c.o.i.) of 0.5%. No phage DNA was detected in the infected AbiK+ cells [Emond, E., Holler, B. J., Boucher, I., Vandenbergh, P. A., Vedamuthu, E. R., Kondo, J. K. & Moineau, S. (1997). Appl Environ Microbiol 63, 1274-1283]. Here, the effects of AbiK are compared on the small isometric-headed phages p2 and P008 (936 species) and on the phage P335 (P335 species). The microbiological impacts of AbiK on p2 were relatively similar to those reported for ul36, with an e.o.p. of 10(6), an 11-fold reduction in the burst size and an e.c.o.i. of 5%. Contrary to phage ul36, replication of phage p2 DNA was observed in the AbiK+ cells. Only immature forms (concatemeric and circular DNA) of phage p2 DNA were found, indicating that the presence of AbiK prevented phage DNA maturation. These distinct molecular consequences of AbiK were also observed for phages P335 and P008, two phages that propagate on the same host. To the knowledge of the authors, this is the first time that different phage responses towards an Abi system have been reported.