Chemical analysis of the surface of microorganisms by X-ray photoelectron spectroscopy

A collection of microorganisms, including a microfungus and various yeasts and bacteria has been analyzed by X-ray photoelectron spectroscopy (XPS). A correlation is observed between the N/P atomic concentration ratio of the cell surface and the cell electrophoretic mobility measured at pH 4, indicating that the dehydrated surface analyzed by XPS is representative of the cell surface in contact with water. Deprotonation of phosphate groups plays a predominant role in the development of the cell negative charge, and carboxylic groups are not involved appreciably; a partial neutralization is allowed by protonation of free amino groups of proteins. These results advocate a broader use of XPS in order to understand physicochemical properties (electrostatic charge, hydrophobicity, ion binding) of the surface of cells, which are of prime importance in various processes occurring in nature and technology.