Use of antisense RNA to confer bacteriophage resistance in dairy starter cultures.

The strategy and implementation of a unique system for engineering bacteriophage resistant starter cultures of Lactococcus lactis employing antisense RNA is reviewed. As a necessary prerequisite for developing this system, we have cloned and sequenced a number of bacteriophage genes coding for minor and major structural proteins. In addition, we have also identified a series of genes whose function(s) is not known but their sequences appear to be conserved in a vast number of isolates. One of these latter sequences, designated gp51C, codes for a 51-kDa protein which is extremely charged and shares some homology with yeast translation initiation factor. Resistance to a broad class of isometric bacteriophages has been achieved by expression of an antisense RNA targeted against, for example, gp51C. In the best case, expression of the antisense gp51C RNA results is a greater than 99% reduction in the total number of plaque forming units. Additional antisense RNA constructs directed against other bacteriophage genes, including the major capsid protein, also appear effective at inhibiting infection from 40-55% suggesting that this approach may prove useful for engineering a set of truly isogenic strains to be used in a starter culture rotation plan.