Aggregatibacter actinomycetemcomitans (Aa) and several pathogenic bacteria attach to abiotic surfaces and produce exopolysaccharide that immobilize the bacterial cells on these colonized surfaces. The exopolysaccharide produced by Aa is made up of ?-1,6-linked N-acetyl-D-glucosamine (GlcNAc) units. Aa produces this exopolysaccharide utilizing a four-gene operon homologous to E. coli pga, Y. pestis hms, and S. epidermidis ica. In Aa, the operon pgaABCD carries a deacetylase enzyme (EC 3.5.1.41) encoded by pagB. Our Preliminary Data show that the enzyme PgaB has the ability to remove acetyl groups from the N-acetyl groups of GlcNAc of PGA. More intriguingly, we discovered that PgaB detaches biofilms and inhibits their formation in Aa as well as S. epidermidis and Actinobacillus pleuropneumoniae. We have previously shown that an enzyme dispersin B (DspB) also from Aa prevents surface attachment of several Gram negative as well as Gram-positive bacterial species through depolymerization of the exopolysaccharide (PGA). Unlike DspB, the newly discovered enzyme PgaB alters the charge state of PGA suggesting that the mechanism of detachment/inhibition might be through the increase of positive charges on the polymer as a result of deacetylation. Importantly, the role of deacetylation in biofilm removal and formation is understudied in these organisms, especially Aa. We will use PgaB from Aa as a model system to understand these processes. Our long-range goal is to understand the role of PGA in Aa pathogenicity. We will use both in vitro as well as in vivo models to test the overall hypothesis that PGA plays a critical role in Aa virulence. Specifically, the following aims will be studied:
Specific Aim 1. Demonstrate that PGA deacetylating enzyme PgaB is critical for Aa biofilm formation.
Specific Aim 2 a. Demonstrate that the state of acetylation of PGA contributes to the biofilm formation in Aa.
Specific Aim 2 b. Establish that PGA contributes to Aa pathogenicity.
Biofilms are a great risk for human health and are responsible most prevalent diseases in humans (caries, gingivitis and periodontal diseases). Understanding the events in biofilm formation is essential in designing strategies in eradicating them. The goal of this research is to understand the role of the exopolysaccharide in the pathogenicity of Aa and in biofilm formation. Specifically, we will delineate the mechanism by which the enzyme deacetylase PgaB, essential for exopolysaccharide synthesis to act as antibiofilm agent. Finally, we will demonstrate how the deacetylase activity of PgaB could be used to understand the role of the exopolysaccharide in A. actinomycetemcomitans virulence.
