Aggregatibacter actinomycetemcomitans (Aa) is a periodontal pathogen that causes Localized Aggressive Periodontitis (LAP) and can cause systemic diseases, such as Infective Endocarditis and abscesses. A striking phenotype of clinical isolates of Aa is tenacious adherence to a wide variety of surfaces. Adherence is correlated with rough colony formation, autoaggregation, and pilus formation. The pili of Aa are termed Flp pili. Biogenesis of Ftp pili is dependent on the tad locus, a 14-gene locus encoding the pilin and machinery allowing for pilus formation and extrusion, tad gene expression is essential for virulence in a rat model of LAP. Although much research has focused on the functions of Tad proteins, little work has been done on the overall regulation of the locus. In this study, regulation of the tad locus will be examined. It has been demonstrated that the promoter of the tad locus is strong and that a termination cascade governs the stoichiometry of some tad gene expression. However, it is unknown if the tad locus is regulated by any tad product or any mechanisms from outside of the locus and what genes are affected downstream of the tad locus. This study aims to identify another regulatory mechanism(s) of the tad locus in Aa. First, the organization of the tad locus will be elucidated through real-time reverse transcriptase PCR and Northern blot analysis. Then a regulator(s) of the tad locus will be identified by a genetic screen encompassing nonessential proteins of Aa and by specifically targeting known regulators of biofilm formation identified in other organisms. Lastly, microarray analysis will be performed to identify genes both co-regulated with and regulated by tad locus expression and biofilm formation. Eludication of a tad locus regulon may lead to identification of novel virulence mechanisms in Aa, as well as in other tad-containing pathogens. Aggregatibacter actinomycetemcomitans is the causative agent of Localized Aggressive Periodontitis, which can lead to tooth loss. Its virulence is dependent on the tad locus, a set of genes, which appears in many other pathogenic bacteria and which is responsible for adherence to surfaces. Examining the regulation of tad locus expression may lead to an understanding of novel virulence mechanisms and may help identify new drug targets in both A. actinomycetemcomitans and other tad-containing pathogens.
