Some authors have explored “Red Queen” models of a co-evolutionary arms race, or fluctuating selection dynamics (FSD), two strategies that may alternate depending on the environmental conditions. It is not so clear, however, how virulent phages, i.e., those that only follow the lytic cycle, achieve coexistence. Temperate phages avoid this by integrating into the host chromosome at a frequency that depends on the environmental conditions. Indeed, prey extinction would unavoidably lead to disappearance of the viral population. Altogether, this study shows how the dynamics between phage and host can be tightly coordinated through an environmental cue, even in the context of a complex biofilm population.Īs highly specialized predators, bacteriophages need to coexist with their bacterial hosts. An acidic pH, together with successful phage propagation, was also necessary to observe the phage-associated changes in biofilm architecture and in the transcriptional profile of the bacterial population. Computer simulation of phage–host dynamics during biofilm development showed how even small differences in pH evolution can affect the outcome of phage infection. This partial phage inactivation seemed to be a consequence of medium acidification due to glucose fermentation by the bacterium. Analysis of phage propagation throughout biofilm development revealed that the number of phage particles increased steadily up to a certain point and then declined. This study aimed to dissect the sequence of events leading to these changes. Previous work had shown that, in some Staphylococcus aureus strains, low concentrations of the virulent phage vB_SauM_phiIPLA-RODI (phiIPLA-RODI) promoted the formation of DNA-rich biofilms, whose cells exhibited significant transcriptional differences compared to an uninfected control.
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