The first step of bacteriophage (phage) infection is the attachment of the phage virion onto a susceptible host cell. This adsorption process is usually described by mass-action kinetics, which implicitly assume an equal influence of host density and adsorption rate on the adsorption process. Therefore, an environment with high host density can be considered as equivalent to a phage endowed with a high adsorption rate, and vice versa. On the basis of this assumption, the effect of adsorption rate on the evolution of phage optimal lysis time can be reinterpreted from previous optimality models on the evolution of optimal lysis time. That is, phage strains with a higher adsorption rate would have a shorter optimal lysis time and vice versa. Isogenic phage lambda-strains with different combinations of six different lysis times (ranging from 29.3 to 68 min), two adsorption rates (9.9 x 10(-9) and 1.3 x 10(-9) phage(-1) cell(-1) ml(-1) min(-1)), and two markers (resulting in "blue" or "white" plaques) were constructed. Various pairwise competitions among these strains were conducted to test the model prediction. As predicted by the reinterpreted model, the results showed that the optimal lysis time is shorter for phage strains with a high adsorption rate and vice versa. Competition between high- and low-adsorption strains also showed that, under current conditions and phenotype configurations, the adsorption rate has a much larger impact on phage relative fitness than the lysis time.
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