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Appl. Environ. Microbiol., Apr 1997, 1274-1283, Vol 63, No. 4
E Emond, BJ Holler, I Boucher, PA Vandenbergh, ER Vedamuthu, JK Kondo and S Moineau
The natural plasmid pSRQ800 isolated from Lactococcus lactis subsp. lactis
W1 conferred strong phage resistance against small isometric phages of the
936 and P335 species when introduced into phage-sensitive L. lactis
strains. It had very limited effect on prolate phages of the c2 species.
The phage resistance mechanism encoded on pSRQ800 is a
temperature-sensitive abortive infection system (Abi). Plasmid pSRQ800 was
mapped, and the Abi genetic determinant was localized on a 4.5-kb EcoRI
fragment. Cloning and sequencing of the 4.5-kb fragment allowed the
identification of two large open reading frames. Deletion mutants showed
that only orf1 was needed to produce the Abi phenotype. orf1 (renamed abiK)
coded for a predicted protein of 599 amino acids (AbiK) with an estimated
molecular size of 71.4 kDa and a pI of 7.98. DNA and protein sequence
alignment programs found no significant homology with databases. However, a
database query based on amino acid composition suggested that AbiK might be
in the same protein family as AbiA. No phage DNA replication nor phage
structural protein production was detected in infected AbiK+ L. lactis
cells. This system is believed to act at or prior to phage DNA replication.
WHen cloned into a high-copy vector, AbiK efficiency increased 100-fold.
AbiK provides another powerful tool that can be useful in controlling
phages during lactococcal fermentations.
Copyright © 1997, American Society for Microbiology
Phenotypic and genetic characterization of the bacteriophage abortive infection mechanism AbiK from Lactococcus lactis
Department of Biochemistry, Faculte des Sciences et Genie, Universite Laval, Quebec, Canada.
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