Membrane potential changes during the first steps of coliphage infection.

Immediately after adsorption, phages T4 and T5 induce a partial depolarization of the host cytoplasmic membrane. Infected bacteria respond to this phage-induced effect by a repolarization that leads to a new steady state of reduced membrane potential. The rate and extent of repolarization are adjusted to the intensity of depolarization, which depends on the number of adsorbed phages. Consequently, the new steady state membrane potential is attained in the same interval of time regardless of the maximum depolarization. These membrane potential changes appear to be independent of phage-specific properties (type of phage, presence of DNA and internal proteins, injection process) and of several membrane-related parameters (temperature, external pH, preinfectious level of membrane potential). We propose that phage adsorption to the outer membrane triggers the emission of a signal that is transmitted to the cytoplasmic membrane. Additivity of independent signals is possible when stimuli (phages) are added at the same time. Additional adsorption of phages has no further depolarizing effect as soon as the repolarization begins. We propose that this refractoriness to secondary depolarization nd the shut-off of the first depolarization are induced by the same chemical modification also initiated by adsorption of the first phage.