Bacteriophage plaques

Matsushima P, Baltt RH. Srreptomyces tipnumii expresses cwo restriction systems that inhibit plasmid transformation and bacteriophage plaque formation. J Bacteriol 1989 171 3128-3132. 

Cells grown to competence (approximately 10" cells/ml) are incubated for about 40 min at 37° with phage DNA at appropriate dilutions. This allows maximum DNA uptake. The interaction between phage DNA and competent cells may be terminated by the addition of DNAse, by an excess of other DNAs which compete for uptake, or by dilution of the incubation mixture. After incubation, transfected cells are diluted appropriately and plated before lysis with indicator bacteria. Bacteriophage plaques can generally be counted and characterized after overnight incubation. 

Figure 26-1 Plaques formed by bacteriophage c )ll growing on Staphylococcus aureus. Each transparent (dark) plaque is the result of lysis of bacteria by the progeny of a single bacteriophage particle. Courtesy of Peter Pattee.

As Ruth Hill observed, the survival of irradiated bacteriophage from UV depends on whether the host bacterium is proficient in excision repair or not, plaque-forming ability being much higher in the former kind of host. This was called host cell reactivation and the bacteria designated hcr+ or her-. 

When a bacteriophage is used as the cloning vector, the gene library is screened as an array of plaques in a bacterial lawn. A hybridization screening method is used similar to that described for plasmid screening above in this case the replica filter is called a plaque lift. ... 

For all chemostat experiments, checks for contamination by other species of bacteria and bacteriophage are recommended. Cells from the chemostat are plated as a lawn in soft agar. After incubation, the lawn is studied for plaques and papillae of other species. Other species can be observed more easily when most of the E. coli are killed by a species-specific bacteriophage. 

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