In situ detection of cell surface hydrophobicity of probe-defined bacteriain activated sludge

The surface hydrophobicity of different types of bacteria in activated slud ge were investigated under in situ conditions by following the adhesion of fluorescent microspheres with defined surface properties to bacterial surfa ces (the MAC-method). This technique was combined with identification of th e bacteria with fluorescence in situ hybridization with rRNA-targeted oligo nucleotides (FISH) and could thus be used for characterization of surface p roperties of probe-defined bacteria directly in a complex system without pr ior enrichment or isolation. This MAC-FISH technique could be used for sing le bacteria as well as filamentous bacteria. In the investigated activated sludge from an industrial wastewater treatment plant, two types of filament ous bacteria dominated. One morphotype consistently attracted only very few hydrophobic microspheres, indicating that the thin sheath of exopolymers a round the cells had a hydrophilic surface. Use of a hierarchical set of gen e probes revealed that these filaments were sulphide oxidising Thiothrix sp p. The other predominating filamentous morphotype had a thick. very hydroph obic exopolymeric sheath. This filamentous bacterium was found to belong to the alpha-Proteobacteria. The relevance of the significant differences in surface hydrophobicity for the two morphotypes in respect to substrate upta ke and flee formation is discussed.