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Surface Charge and Hydrophobicity of Endospores of Bacillus anthracis and Related Species in Aqueous Solution
Citation:
White, C., J. Popovici, D. A. LYTLE, AND E. W. RICE. Surface Charge and Hydrophobicity of Endospores of Bacillus anthracis and Related Species in Aqueous Solution. Presented at AWWA Annual Conference and Exposition, Dallas, TX, June 10 - 14, 2012.
Impact/Purpose:
To inform the public.
Description:
The surface properties of microorganisms play an important role in attachment and detachment in the environment. The change in surface charge can effect coagulation, disinfection, adhesion to surfaces, uptake of chemicals, and environmental transport. In aqueous solution, cell surface charge is dependent on a number of factors including ionic strength, ion valence, pH, and organic load. Cell hydrophobicity is driven by structures such as protein, oligosaccharides, and appendages and is likewise affected by water chemistry. An organism’s hydrophobicity contributes to its biofilm forming potential and pathogenicity. In drinking water distribution systems, there exists a variety of surfaces for bacterial attachment allowing hydrophobic organisms to form biofilms, evade disinfection, and alter water quality. Bacterial endospores are of particular interest due to their resistance to disinfection compared to vegetative cells. These properties make endospores an attractive bioterrorism agent and worthy of investigation. In this study electrophoretic light scattering and microbial adhesion to hydrocarbon was used to measure the electrophoretic mobility and hydrophobicity of endospores of 6 Bacillus species. Endospores were measured in aqueous solution across a range of pH and ionic strength. Results suggest that surface charge is a unique trait. Electrophoretic mobilities formed 3 distinct groups that parallel 16S ribosomal phylogeny. Specifically, group one consisted of B. anthracis, group two consisted of B. cereus and B. thuringiensis and group three of B. globigii, B. megaterium, and B. subtilis. The data show pH dependence of electrophoretic mobility below pH 6. The point zero charge of all spores was at low pH (less than 3). Electrophoretic mobilities were less negative in high ionic strength solutions compared to low ionic strength solutions. Hydrophobicity did not trend with electrophoretic mobility at pH 8 in the buffer tested. Results will be discussed in comparison to tests performed in dechlorinated drinking water. The data presented can be applied to environmental attachment/detachment and transport models, as well as the food industry. Appropriate surrogate selection for laboratory studies utilizing endospores will also be discussed.
