The Lactococcal Abortive Phage Infection System AbiP Prevents both Phage DNA Replication and Temporal Transcription Switch

Abstract

We describe here a new lactococcal abortive phage infection system, designated AbiP. AbiP is effective against some lactococcal phages of one prevalent group, 936, but not against phages from the other two groups (c6A and P335 Dairy fermentations using lactococci are highly susceptible to bacteriophage attacks. Therefore, special attention has been given to lactococcal phage defense mechanisms and in particular to abortive phage infection systems (Abi). These systems arrest phage multiplication and cause premature cell death upon infection. This decreases the number of progeny particles produced and limits their spread to other cells. As a consequence, the cell population survives (reviewed in references 32 and 39).Twenty-two lactococcal Abi genes, designated abiA to abiT, have been described (7, 9, 43; for a review, see reference 20). Three of these (abiD, abiD1, and abiF) code for proteins sharing 28 to 46% identity throughout the protein sequence. Similarly, AbiA and AbiK share 23% identity. Putative products of the other abi genes show no homology. Lactococcal phages fall into three prevalent groups of DNA homology (29). Two of these groups, designated 936 and c6A, are composed of virulent phages responsible for industrial fermentation failures, and the third, designated P335, is composed mostly of temperate phages. Phages from one of these groups share essentially no DNA homology with members of the other groups (13).

A Phage Protein Confers Resistance to the Lactococcal Abortive Infection Mechanism AbiP

“…AbiP has recently been shown to block phage bIL66M1 DNA replication 10 min after infection and to prevent the early transcription switch-off (14). Here we show that the early expressed phage bIL170 e6 gene (e6 bIL170 ) confers resistance to AbiP (AbiP r ) and is readily transferred to AbiP-sensitive (AbiP s ) phages during coinfection.…”

“…Here we show that the early expressed phage bIL170 e6 gene (e6 bIL170 ) confers resistance to AbiP (AbiP r ) and is readily transferred to AbiP-sensitive (AbiP s ) phages during coinfection. AbiP is active on lactococcal phages of the 936 group (19), bIL41, bIL66M1, and sk1 but not on bIL170 (14). Phages of this group share homology over 90 to 92% of their genome length (9).…”

“…In particular, they frequently possess bacteriophage abortive infection mechanisms (Abi) (4,6,15,28) that interrupt an intracellular step of phage multiplication, leading to death of the infected cell and survival of the bacterial population (23,27). Functional studies of these mechanisms have revealed a great diversity in their modes of action (14).…”

“…In order to determine the phage region(s) involved in sensitivity or resistance to AbiP, we first tried to isolate spontaneous AbiP r mutants from phage bIL41, bIL66M1, or sk1. Phages, AbiP Ϫ plasmid-free L. lactis strains IL1403 (8) and MG1363 (16), AbiP ϩ derivatives IL1403(pIL2617) and MG1363(pIL2617), and growth conditions were previously described (14). AbiP s phages form barely visible turbid plaques (typical of the sensitivity to an Abi mechanism), while AbiP r phages form easily recognizable clear plaques.…”

“…In a first experiment, IL1403(pIL1201, pIL352), expressing both AbiB (10,25) and AbiP (14), was coinfected with phages bIL41 (AbiB r and AbiP s ) and bIL170 (AbiB s and AbiP r ). Progeny phages formed plaques on the same strain.…”