A synthesis of the divalent cation requirements for efficient adsorption of bacteriophage onto bacterial cells

As the first step of bacteriophage infection, understanding the mechanics of adsorption of phages is vital for successful therapeutic phage treatments. It is also important for efficient scale-up of phages for industrial applications. It was understood early on that bacteriophage required divalent cations for successful adsorption. The mechanics of this process however are still vague; for some phage it may just be to negate negative electrostatic forces, for others it may also be specific for enzymatic and/or conformational changes. While many phages require divalent cations, the specificity of the ions and the concentrations differs between them. The adsorption efficiency of Ca2+ was superior in most studies to Mg2+ and other cations but the exact mechanisms are unresolved. The efficiency of Ca2+ might in general, explain why it is relatively easy to isolate phages from marine bacteria grown on marine salt based medium with high Ca2+/Mg2+ content. Too low a concentration of cations is insufficient for adsorption, and too high a concentration blocks adsorption. Of the monovalent cations, only H+ (pH) has been recorded to have a marked influence on adsorption. Phages become inactive and tend to aggregate at low pH and we hypothesise this is due to competitive exclusion interactions with Ca2+ or other bivalent cations. Whilst data are limited, the divalent cation optimum concentrations range between 0.01 and 10mM. Some phages like T4 phage may utilize organic substances such as L-tryptophan as a co-factor.