Involvement of the LlaKR2I Methylase in Expression of the AbiR Bacteriophage Defense System in Lactococcus lactis subsp. lactis biovar diacetylactis KR2

Abstract

The native lactococcal plasmid, pKR223, from Lactococcus lactis subsp. lactis biovar diacetylactis KR2 encodes two distinct bacteriophage-resistant mechanisms, the LlaKR2I restriction and modification (R/M) system and the abortive infection (Abi) mechanism, AbiR, that impedes bacteriophage DNA replication. This study completed the characterization of AbiR, revealing that it is the first Abi system to be encoded by three genes, abiRa, abiRb, and abiRc, arranged in an operon and that it requires the methylase gene from the LlaKR2I R/M system. An analysis of deletion and insertion clones demonstrated that the AbiR operon was toxic in L. lactis without the presence of the LlaKR2I methylase, which is required to protect L. lactis from AbiR toxicity. The novelty of the AbiR system resides in its original gene organization and the unusual protective role of the LlaKR2I methylase. Interestingly, the AbiR genetic determinants are flanked by two IS982 elements generating a likely transposable AbiR composite. This observation not only substantiated the novel function of the LlaKR2I methylase in the AbiR system but also illustrated the evolution of the LlaKR2I methylase toward a new and separate cellular function. This unique structure of both the LlaKR2I R/M system and the AbiR system may have contributed to the evolution of the LlaKR2I methylase toward a novel role comparable to that of the cell cycle-regulated methylases that include Dam and CcrM methylases. This new role for the LlaKR2I methylase offers a unique snapshot into the evolution of the cell cycle-regulated methylases from an existing R/M system.

Structure and activity of AbiQ, a lactococcal endoribonuclease belonging to the type III toxin–antitoxin system

“…Lactococcus lactis has been a productive model to discover abortive mechanisms as 23 different lactococcal Abi systems have been reported (Chopin et al ., ; Durmaz and Klaenhammer, ; Holubova and Josephsen, ; Haaber et al ., ). Usually, the resistance phenotype is mediated by a single host gene, except for AbiE, AbiG, AbiL, AbiT and AbiU, which are encoded by two genes, AbiR, encoded by possibly four genes and AbiS, composed of a specific DNA structure (Dai et al ., ; Josephsen and Neve, ; Chopin et al ., ; Yang et al ., ). Most of these genes have been found on plasmids (Chopin et al ., ).…”

Activation of mRNA translation by phage protein and low temperature: the case of Lactococcus lactis abortive infection system AbiD1

“…A slight increase of specific transcript after phage infection was demonstrated only for abiP gene [ 26 ]. However, some experimental data suggests post-transcriptional regulation of expression and/or function of lactococcal abi s. AbiR requires an associated methylase to protect the host from its own action [ 21 ]. Cloning of intact abiG was shown to be lethal for heterologous E. coli cells [ 25 ].…”

Potential of AbiS as defence mechanism determined by conductivity measurement

“…The observed difference in efficiencies can also be caused by the fact that MG1614[pCH1, pAW122] contains two similar Abi systems in contrary to MG1614[pCH1, pJW566], which contains AbiS in combination with an R/M system. Many other groups have shown that the addition of R/M system with an Abi system in the same strain can significantly improved the phage resistance phenotype in L. lactis (Yang et al . 2006; Durmaz and Klaenhammer 2007).…”

“…2006). Other phenotypic characteristics can include reduction in plaque size due to decreased burst size of the bacteriophage, and may or may not have a reduction in the efficiency of plaquing (EOP) of the bacteriophage (Yang et al . 2006).…”