Abstract
It is generally thought that the adsorption rate of a bacteriophage correlates positively with fitness, but this view neglects that most phages rely only on exponentially growing bacteria for productive infections. Thus, phages must cope with the environmental stochasticity that is their hosts’ physiological state. If lysogeny is one alternative, it is unclear how strictly lytic phages can survive the host stationary phase. Three scenarios may explain their maintenance: (1) pseudolysogeny, (2) diversified, or (3) conservative bet hedging. To better understand how a strictly lytic phage survives the stationary phase of its host, and how phage adsorption rate impacts this survival, we challenged two strictly lytic phage λ, differing in their adsorption rates, with stationary phase Escherichia coli cells. Our results showed that, pseudolysogeny was not responsible for phage survival and that, contrary to our expectation, high adsorption rate was not more detrimental during stationary phase than low adsorption rate. Interestingly, this last observation was due to the presence of the “residual fraction” (phages exhibiting extremely low adsorption rates), protecting phage populations from extinction. Whether this cryptic phenotypic variation is an adaptation (diversified bet hedging) or merely reflecting unavoidable defects during protein synthesis remains an open question.
Highlights
It is argued that in an environment of homogeneous mixing, such as a liquid culture, a bacteriophage should evolve toward a high adsorption rate to maximize its fitness (Shao and Wang 2008)
THROUGHOUT THE HOST GROWTH CYCLE To estimate the effect of adsorption rate on phage fitness during E. coli’s entire growth cycle we used two isogenic λ strains that differ in their adsorption rates, as a consequence of the presence or absence of the sidetail fibers (Stf) (Hendrix and Duda 1992; Shao and Wang 2008)
Our previous results showed that Stf+ phage has a much higher adsorption rate than the Stf− phage, whether the host cells are in the exponential phase (Shao and Wang 2008) or the stationary phase (Gallet et al 2009)
Summary
It is argued that in an environment of homogeneous mixing, such as a liquid culture, a bacteriophage (phage) should evolve toward a high adsorption rate to maximize its fitness (Shao and Wang 2008). The adsorption rates for the Stf+ and Stf− phages have been previously estimated with either the exponentially growing host (Shao and Wang 2008) or the stationary phase host (Gallet et al 2009).
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