The toluene-degrading bacterium Acinetobacter sp. Tol 5 shows a highly adhesive and autoagglutinating nature through cell surface nanofibers. In the present study, various aspects of the adhesiveness of To! 5 cells were evaluated, namely, the association with biofilm formation, the specificity, and the effects of additives. During growth, Tol 5 and Pseudomonas aeruginosa PAO1 cells showed high capacities to form biofilms. However, resting PAO1 cells barely adhered to a polystyrene (PS) surface, while a large number of resting Tol 5 cells rapidly adhered. This implies that Tol 5 cells are intrinsically adhesive and that their initial attachment ability is quite high and distinguishable from their ability to form biofilm. This high adhesiveness of Tol 5 cells was considered to be nonspecific because the cells adhered to various material surfaces from hydrophobic plastic surfaces to hydrophilic glass and metal surfaces. However, Tol 5 cells were found not to be adhesive to Escherichia coil cells. Although Tol 5 cells were capable of interspecies interaction and coagglutination with E. coil cells, at the surface of cell clumps, E. coil cells localized, suggesting that they disturbed autoagglutination of Tol 5 cells. Tol 5 has a hydrophobic cell surface. However, the addition of nonionic surfactant Triton X-100 and bovine serum albumin increased the adhesion of 'Tol 5 cells to a PS surface, in contrast to previous reports of hydrophobic bacteria. The results highlighted the interesting features of adhesiveness of Tol 5 cells. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.