Research Article
1 April 1994

Phenotypic Consequences of Altering the Copy Number of abiA, a Gene Responsible for Aborting Bacteriophage Infections in Lactococcus lactis

Abstract

The abiA gene (formerly hsp) encodes an abortive phage infection mechanism which inhibits phage DNA replication. To analyze the effects of varying the abiA gene dosage on bacteriophage resistance in Lactococcus lactis, various genetic constructions were made. An IS946-based integration vector, pTRK75, was used to integrate a single copy of abiA into the chromosomes of two lactococcal strains, MG1363 and NCK203. In both strains, a single copy of abiA did not confer any significant phage resistance on the host except for one of the MG1363 integrants, NCK625, which exhibited a slightly higher level of resistance to phages sk1 and p2. Hybridization of the total cellular RNA from NCK625 to an abiA-specific probe indicated that the integration took place downstream of a promoter causing stronger expression of abiA in this integrant. Three abiA-containing plasmids of various copy numbers were introduced into both strains, and the recombinants were evaluated for resistance to phages c2, p2, sk1, and φ31. Plasmid pTRK18 has a copy number of approximately six (cn = 6) and caused a decreased plaque size for all phages evaluated. Integration of pTRK75 into a native plasmid of NCK203 generated pTRK362 (cn = 13), which caused a reduced efficiency of plaquing (EOP = 10-2) and reduced plaque size. A high-copy-number abiA plasmid (pTRK363), based on the pAMβ1 origin of replication, was also constructed (cn = 100). Plasmid pTRK363 caused a significant reduction in EOP (10-4 to 10-8) and plaque size for all phages tested, although in some cases, this plasmid caused the evolution of AbiA-resistant phage derivatives. Altering the gene dosage or expression level of abiA significantly affects the phage resistance levels.

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Published In

cover image Applied and Environmental Microbiology
Applied and Environmental Microbiology
Volume 60Number 4April 1994
Pages: 1129 - 1136
PubMed: 16349225

History

Published online: 1 April 1994

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Contributors

Authors

Polly K. Dinsmore
Department of Food Science, Southeast Dairy Foods Research Center, North Carolina State University, Box 7624, Raleigh, North Carolina 27695
Todd R. Klaenhammer
Department of Food Science, Southeast Dairy Foods Research Center, North Carolina State University, Box 7624, Raleigh, North Carolina 27695
Department of Microbiology, Southeast Dairy Foods Research Center, North Carolina State University, Box 7624, Raleigh, North Carolina 27695

Notes

Paper FSR-92-47 of the Journal Series of the Department of Food Science, North Carolina State University, Raleigh.

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