Lactococcal Phage Genes Involved in Sensitivity to AbiK and Their Relation to Single-Strand Annealing Proteins

Abstract

Lactococcal phage mutants insensitive to the antiviral abortive infection mechanism AbiK are divided into two classes. One comprises virulent phages that result from DNA exchanges between a virulent phage and the host chromosome. Here, we report the analysis of the second class of phage mutants, which are insensitive to AbiK as a result of a single nucleotide change causing an amino acid substitution. The mutated genes occupy the same position in the various lactococcal phage genomes, but the deduced proteins do not share amino acid sequence similarity. Four nonsimilar proteins involved in the sensitivity to AbiK (Sak) were identified. Two of these Sak proteins are related to Erf and RAD52, single-strand annealing proteins involved in homologous recombination.Lactococcus lactis strains used in the manufacture of fermented dairy products are susceptible to infection by virulent bacteriophages, which can interrupt the fermentation process. Members of three genetically distinct lactococcal phage groups are repeatedly isolated from unsuccessful dairy fermentations, namely species 936, c2, and P335 (18). Bacteria are also known to possess defense barriers against phage infection. More than 50 natural L. lactis phage resistance systems have been characterized, and they are divided into four groups according to the time at which they act during the lytic cycle (10). They include the inhibition of phage adsorption, blocking of DNA ejection, restriction and modification systems, and abortive infection mechanisms (Abi) (10). The Abi systems form a heterogeneous group that includes all cell defenses that act after DNA ejection into the cytoplasm and lead to cell death (10). To date, over 20 distinct Abi systems have been cloned and sequenced in Lactococcus, but little is known about the molecular mechanisms used by Abi proteins to block phage infection.Two general types of phage mutants can be obtained through the selective pressure of Abi systems. The first class is obtained only with P335-like phages, and these mutants result from homologous recombination with phage-related sequences present in the host chromosome (5,6,11,12,21). To date, these recombination mutants have been isolated during the study of AbiA, AbiC, AbiK, and AbiT only. The second class is found in members of the three groups, and these phages carry only point mutations. Their characterization led to the identification of phage elements that are involved in the sensitivity to lactococcal Abi systems. Two AbiA-insensitive derivatives of phage 31 (species P335) bearing point mutations have been characterized, and the presence of the mutated intergenic region or orf245 of the bacteriophage reduced the efficacy of AbiA (11). On the other hand, the efficacy of AbiD1 was increased by the expression of the wild-type orf1 of phage bIL66 (species 936) (3). AbiK-insensitive class I phage mutants have been characterized previously (6). Here, 10 AbiK-insensitive class II phage derivatives were isolated and analyzed.Isolation and characterization of AbiK-insensitive ...

Genome Sequence and Global Gene Expression of Q54, a New Phage Species Linking the 936 and c2 Phage Species ofLactococcus lactis

“…ZP_00382242). Similarities were also found with proteins of the essential recombination factor (ERF) family, including Sak2 from phage P335 (44% identity; 67/152) (8). A conserved ERF domain (pfam04404) was also identified in ORF11.…”

An Unexplored Diversity of Reverse Transcriptases in Bacteria

“…This conclusion is based on the diverse sequences of the four sak genes and the fact that the resistance mutations occur throughout the sak sequences (98). However, the precise nature of the interaction remains unclear, as does the overall mechanism by which AbiK mediates immunity to phages.…”

Genomics of Bacterial and Archaeal Viruses: Dynamics within the Prokaryotic Virosphere

“…Plasmids, on the other hand, might encode factors that abolish viral replication in a number of different ways (45,69,114,282). Viruses return the favor by encoding antirestriction proteins or evolving toward resistance to the detrimental effects of these factors (25,245,281). There is therefore a constant struggle between viruses and plasmids inside the cells which drives the evolution of both the mobile elements and their hosts.…”