Effect of temperature on bacteriophage-mediated lysis efficiency with a special emphasis on bacterial temperature history

Despite the great potential of phages as biocontrol agents, there is much uncertainty about the environmental factors influencing lysis efficiency. In this study we investigated the effect of temperature using three distinct lytic E. coli phages that were isolated from a single environmental water sample. All three were identified as dsDNA phages belonging to the Myoviridae family. Whereas the optimal growth temperature of E. coli is well known to be 37 ˚C and exposure of phages (prior to mixing with bacteria) to temperatures between 4 and 37˚C did not affect their infectivity, plaque sizes and numbers greatly decreased with increasing incubation temperature (20˚C, 30˚C, 37˚C) of the phage-host mix. At 37˚C, no visible plaques were observed. Results suggest that temperature sensitivity of the phage-host interaction is distinct from the temperature susceptibility of the two players and corroborate previous reports that highest lysis rates are obtained at temperatures approximate with ambient conditions of the phage environment. Infectivity was however found not only to depend on the incubation temperature of the phage-host mix, but also on the bacterial temperature history. Moreover, exposure of bacteria to heat stress prior to phage challenge resulted in a phage-resistant phenotype raising the question whether bacterial pathogens shed from warm-blooded hosts might be less susceptible to phages adapted to environmental temperature conditions.