Can phages be cheated? - A study on the influence of inducing molecules on bacteriophage propagation at low host cell densities

Abstract

It has been reported in vitro that bacteriophages require a certain host cell density in order to propagate. However, previous studies have shown that in environment, especially in water bodies, bacteriophage infection takes place even when host cell densities are lower than the required threshold density observed in vitro. This leads to the indication that some factors must be in play that allows bacteriophages to propagate at such low host cell densities in the environment. In this study we investigated the effect of host cell densities on bacteriophage propagation in phage-host systems of Vibrio spp. and Shiga toxin-producing Escherichia coli (STEC) and determined the respective threshold densities. We found that phage propagation ceased at host cell densities beyond the threshold density but did initiate when supplemented with spent media of the respective phage and host cultures at the logarithmic phase of infection. Hence, we hypothesize that molecules produced by the host and/or phage have the ability to influence how bacteriophages take decision to infect its host cell, especially in the environment. Although we investigated the effect of these molecules in the phage-host system of Vibrio spp. only, similar studies with phage-host systems of different species may provide valuable insights to our understanding of phage-host interaction and therefore may contribute to the field of phage therapy.