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Appl. Environ. Microbiol., Apr 1995, 1266-1273, Vol 61, No. 4
E Durmaz and TR Klaenhammer
Three derivatives of Lactococcus lactis subsp. lactis NCK203, each with a
different pair of restriction/ modification (R/M) and abortive infection
(Abi) phage defense systems, were constructed and then rotated in repeated
cycles of a milk starter culture activity test (SAT). The rotation
proceeded successfully through nine successive SATs in the presence of
phage and whey containing phage from previous cycles. Lactococcus cultures
were challenged with 2 small isometric-headed phages, (phi)31 and ul36, in
one rotation series and with a composite of 10 industrial phages in another
series. Two native lactococcal R(sup+)/M(sup+) plasmids, pTRK68 and pTRK11,
and one recombinant plasmid, pTRK308, harboring a third distinct R/M system
were incorporated into three NCK203 derivatives constructed separately for
the rotation. The R(sup+)/M(sup+) NCK203 derivatives were transformed with
high-copy-number plasmids encoding four Abi genes, abiA, abiC, per31, and
per50. Various Abi and R/M combinations constructed in NCK203 were
evaluated for their effects on cell growth, level of phage resistance, and
retardation of phage development during repeated cycles of the SAT. The
three NCK203 derivatives chosen for use in the SAT exhibited additive
effects of the R/M and Abi phenotypes against sensitive phages. In such
combinations, phage escaping restriction are prevented from completing
their infective cycle by an abortive response that kills the host cell. The
rotation series successfully controlled modified, recombinant, and mutant
phages which were resistant to any one of the individual defense systems by
presenting a different set of R/M and Abi defenses in the next test of the
rotation.
Copyright © 1995, American Society for Microbiology
A Starter Culture Rotation Strategy Incorporating Paired Restriction/ Modification and Abortive Infection Bacteriophage Defenses in a Single Lactococcus lactis Strain
Department of Food Science, Southeast Dairy Foods Research Center, North Carolina State University, Raleigh, North Carolina 27695-7624
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