Adsorption of the defective phage PBS Z1 to Bacillus subtilis 168 Wt.

Three aspects of the adsorption of the defective phage PBS Z1 to Bacillus subtilis 168 Wt have been investigated. These are the kinetics, the number of receptors on the cell wall and the character of these receptors. The reaction constants for the binding of phages onto receptors, for the dissociation of the phage-receptor complex and for the transition from reversible to irreversible binding of the phages were calculated from adsorption curves obtained by an enzyme-linked immunosorbent assay (ELISA). They were 1.8 x 10(-13), 6.7 x 10(-2) and 9.0 x 10(-3) respectively. The maximum number of phages adsorbed per cell was 2700, a number limited by the surface area of the cells. Apart from the receptors on the cell wall, receptors on the cell membrane were found. This was concluded from additional adsorption experiments with stable L-forms and contracted phages. Based on these results, together with data from the literature on bacteriocins, phage ghosts and yeast killer factors, a hypothesis concerning the first stage of killing by defective phages has been formulated.