Degree Name

Master of Science (MS)

Semester of Degree Completion


Thesis Director

Kandy D. Baumgardner


The lambdoid bacteriophages are ideal subjects for the study of populational interactions at the molecular level because they do not mutually exclude one another in mixed infection of the same host cell. Previous work done in this laboratory using the lambdoid phage pairs λ-434 hy mi and λ-80 have demonstrated a density-dependent reduction in progeny yield per infected cell (burst size) as a function of increasing multiplicity of infection (m.o.i.). The λ cI gene which codes for the repress or molecule has been demonstrated to be the cause of the interaction in the λ-434 hy mi phage pair.

The purpose of this research was to determine if the λ cI gene is also responsible for the interaction observed in the λ-80 phage pair. The λ cII gene which also functions in an immunity specific manner was also considered as a source of interaction. The experiments were conducted using the mutant phages λcI857 and 434 hy cII68, a hybrid phage consisting of the 434 immunity region in an otherwise λ genome. By comparing the lines generated on a log-log plot of burst size versus m.o.i. it is possible to determine whether these phages deficient in the λ cI or cII genes produced results similar to the interaction observed in the wild type phage pairs. If the interaction is seen to be eliminated by the use of a mutant phage, then the interaction is dependent upon the gene that is deficient in that mutant phage.

The results of this study indicate that the interaction observed in the λ-80 phage pair is not dependent upon the λ cI or cII genes. Neither mutant phage alleviated the density-dependent decrease in burst size. This suggests that some vegetative gene is responsible for the observed interaction. It is postulated that the most likely candidates are the DNA replication genes (O and P) and the gene (Q) which controls late phage transcriptions.