Bacteria often utilize polysaccharides as adhesive structures to attach to surfaces, to form biofilms, and to infect host cells. In addition, polysaccharides hold strong promise as biological adhesives in many areas of human activity, including as dental and surgical adhesives. The bacterium Caulobacter crescentus synthesizes a polysaccharide called the holdfast that exhibits and impressive adhesive force. Contrary to most commercial adhesives, holdfasts adhere tightly to a variety of surfaces in both freshwater and marine environments. Such a property is critical for medical applications in the human body. The general goal of this research is to use a multidisciplinary approach ranging from genetics to biophysics to study the chemical and biophysical basis for holdfast properties and to understand how holdfast properties are modulated by deacetylation and inhibition by extracellular DNA (eDNA). The project has three specific aims.
The first aim i s to determine the biophysical basis for holdfast adhesiveness. Atomic force microscopy (AFM) will be used to systematically study the influence of surface roughness, shear stress, surface composition, ionic strength, and pH on holdfast adhesion in order to provide a better understanding of the mechanism of holdfast adhesion and adhesion control.
The second aim i s to determine the role of deacetylation in holdfast anchoring and adhesive properties. A holdfast polysaccharide deacetylase mutant causes the release of non-adherent holdfast in solution. The composition and structure of the holdfast polysaccharide will be determined from normal and deacetylase mutant cells. AFM force spectroscopy and high-resolution fluorescence microscopy will be used to determine the role of deacetylation on holdfast adhesiveness and cohesiveness. Biochemical experiments will be used to study the role of deacetylation in anchoring the holdfast to the cell. Finally, similar studies of the holdfast of marine species will provide better biomaterials for potential applications in the saline environment of the human body.
The third aim i s to determine the biological basis for the recently discovered mechanism of eDNA inhibition of holdfast adherence. The role of a toxin-antitoxin system in the production of eDNA by programmed cell death will be studied and the basis for the sequence specificity of holdfast inhibition will be determined. AFM indentation studies and simultaneous AFM imaging and Raman scattering spectroscopy of holdfasts bound or not to eDNA will be used to determine how specific DNA alters the structure and structural properties of the holdfast. Results from the proposed studies will provide insight into the basic mechanisms for the impressive adhesive properties of the holdfast and modulation of these properties, paving the way for the future development of the holdfast as a biological adhesive. In addition, results of these studies will provide insights into the mechanism of polysaccharide adhesiveness in general, as well as for strategies to inhibit polysaccharide adhesion, for example during infection by pathogens.
Bacteria often utilize polysaccharides as adhesive structures to attach to surfaces, to form biofilms, and to infect host cells, and these polysaccharides hold strong promise as biological adhesives in many areas of human activity, including as dental and surgical adhesives. We will study one of the strongest known biological adhesives, the holdfast polysaccharide of Caulobacter crescentus by investigating the chemical and the biophysical basis for holdfast properties and the mechanism of action of a specific inhibitor of holdfast adhesiveness. These studies will provide data essential to the design of strategies to use polysaccharides in various applications, as well as strategies to inhibit polysaccharide adhesion during infection by bacterial pathogens.
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