By using the first-order rate equations to describe the reactions of (where B, P, BP, and BP* are bacteria, free phage, transient, and stable phage-bacterium complexes, respectively), Moldovan

et al. [50] estimated the adsorption (k), desorption (k’), and irreversible-binding rates for phage λ to be at the orders of 10-11 (mL/s), 10-3 (1/s), and 10-3 (1/s), respectively (their Table 1). Therefore, for phage λ, it is the initial recognition between the phage tail fiber and bacterial receptor that is the “”rate-limiting”" step in phage adsorption. That is, the different adsorption rates among our isogenic λ strains are likely due to differences in k, rather than k’ or k”. It HSP990 is unlikely that the presence of agar in the immediate vicinity of a phage virion and a bacterium would drastically alter the recognition process. Even though agar is much more viscous than the liquid medium, the phage diffusivity in agar should be NU7026 solubility dmso impacted to the same degree across all our Stf+ or Stf- phages, as described by the Stokes-Einstein equation [50–52], which stated that the solvent (agar) viscosity and the solute diffusion coefficient (phage diffusivity) are inversely related to each other. Taken together, it seems probable that even if the adsorption rate JQ-EZ-05 estimated in agar is different from the one estimated in liquid culture, the difference may not

be too large. In our ratio comparisons, we used the endpoint plaque size for our test, rather than the velocity of plaque wavefront, which is what has actually been modeled. It is not clear how this discrepancy may contribute to model failure. But it is to be noted that, except in few cases like phage T7, the velocity of plaque wavefront may not be as easily determined

as the endpoint plaque size (but see [53]). Many of the models are simplified versions oxyclozanide of a much complex general model, therefore, their predictions are only valid under restricted conditions. The failure of model predictions may simply reflect the fact that our experimental conditions violated the model assumptions. However, the almost universal failure of all models suggests that it may not be simply the result of assumption violations. Implications for phage ecology and evolution The plaque size, productivity, and concentration are all aftereffects of the combined action of various phage traits. However, except in the case of artificial selection for, say, large plaque size for ease of manipulations [54], it is not clear how natural selection would act on these aftereffects so that various phage traits could be selected as a result. One possible selection scenario is the periodic destruction of biofilm habitat and its concomitant dispersion of the phage inhabitants. The experimental equivalent of this scenario is the homogenization of the top agar gel containing plaques and the extraction of the total phages for subsequent plating.