Actinobacillus actinomycetemcomitans (Aalpha) is a gram-negative bacterium that has been closely associated with several forms of periodontal disease in man. Numerous virulence factors have been attributed to Aalpha including: a leukotoxin, an endotoxin, a bone resorbing factor, a capsule, a collagenase, acid and alkaline phosphatases, a fibroblast inhibitory factor, a lymphocyte suppressive factor, and an immunoregulatory serotype- specific surface antigen. Efforts to understand the genetic determinants for these factors are hindered by the presence of transiently integrated exogenous genetic elements in Aalpha, in the form of prophages. When temperate bacterial viruses lysogenize bacteria, the prophages formed frequently confer new properties on the bacteria that they infect. Very often, these new properties significantly increase the pathogenicity of the host cell. Properties such as toxin production, toxin release, serum sensitivity, altered outer membrane structure, altered antigenicity, and altered capsule formation, are all known to be mediated by bacteriophage infection. Recent findings suggest that bacteriophage infection is widespread among Aalpha strains. Consequently, without knowing which Aalpha strains are lysogenic and which (if any) are not, it would be difficult, if not impossible to know which virulence factors are intrinsic to Aslpha, and which are attributable to the expression of exogenous genetic information brought into the cell by viral infection. The experiments described in this proposal are designed to determine the distribution of viral infection among strains of Aalpha. They will identify those Aalpha strains that are lysogenic and those that are bacteriophage-free. Since there are at least 4 different Aalpha bacteriophages known, the procedures proposed in this application are also directed towards identifying the distribution of each of the known Aalpha bacteriophages among the lysogenic Aalpha strains. Representative isolates of each of the known Aalpha morphotypes (A, B1, B2, C) will be obtained from induced Aalpha lysogens. DNA probes prepared from the genomes of each of the Aalpha phages will be used to screen Aalpha strains for DNA sequences homologous to the phage DNA, thereby identifying Aalpha lysogens. Furthermore, curing procedures will be employed to eliminated phage infection from lysogenic strains. These procedures are expected to result in the generation of Aalpha strains of defined genetic constitution in terms of bacterial virus infection. Such Aalpha strains will then be available to the research community for determining the genetic basis for virulence in Alpha.