Molecular characterization of a second abortive phage resistance gene present in Lactococcus lactis subsp. lactis ME2.
The fifth phage resistance factor from the prototype phage-insensitive strain Lactococcus lactis subsp. lactis ME2 has been characterized and sequenced. The genetic determinant for Prf (phage resistance five) was subcloned from the conjugative plasmid pTN20, which also encodes a restriction and modification system. Typical of other abortive resistance mechanisms, Prf reduces the efficiency of plaquing to 10(-2) to 10(-3) and decreases the plaque size and burst size of the small isometric-headed phage p2 in L. lactis subsp. lactis LM0230. However, normal-size plaques occurred at a frequency of 10(-4) and contained mutant phages that were resistant to Prf, even after repeated propagation through a sensitive host. Prf does not prevent phage adsorption or promote restriction and modification activities, but 90% of Prf+ cells infected with phage p2 die. Thus, phage infections in Prf+ cells are aborted. Prf is effective in both L. lactis subsp. lactis and L. lactis subsp. cremoris strains against several small isometric-headed phages but not against prolate-headed phages. The Prf determinant was localized by Tn5 mutagenesis and subcloning. DNA sequencing identified a 1,056-nucleotide structural gene designated abiC. Prf+ expression was obtained when abiC was subcloned into the lactococcal expression vector pMG36e. abiC is distinct from two other lactococcal abortive phage resistance genes, abiA (Hsp+, from L. lactis subsp. lactis ME2) and abi416 (Abi+, from L. lactis subsp. lactis IL416). Unlike abiA, the action of abiC does not appear to affect DNA replication. Thus, abiC represents a second abortive system found in ME2 that acts at a different point of the phage lytic cycle.
Durmaz
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Department of Food Science North Carolina State University, Raleigh 27695-7624.
Higgins
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Klaenhammer
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D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001435:Bacteriophages / Q000235:genetics / Q000254:growth & development*; D001483:Base Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D004261:DNA Replication; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D013294:Lactococcus lactis / Q000235:genetics* / Q000254:growth & development; D008969:Molecular Sequence Data; D010957:Plasmids; D015183:Restriction Mapping
D001426:Bacterial Proteins; C078090:abiC protein, Lactococcus lactis