Fitness benefits of low infectivity in a spatially structured population of bacteriophages

Abstract

For a parasite evolving in a spatially structured environment, an evolutionarily advantageous strategy may be to reduce its transmission rate or infectivity. We demonstrate this empirically using bacteriophage (phage) from an evolution experiment where spatial structure was maintained over 550 phage generations on agar plates. We found that a single substitution in the major capsid protein led to slower adsorption of phage to host cells with no change in lysis time or burst size. Plaques formed by phage isolates containing this mutation were not only larger but also contained more phage per unit area. Using a spatially explicit, individual-based model, we showed that when there is a trade-off between adsorption and diffusion (i.e. less 'sticky' phage diffuse further), slow adsorption can maximize plaque size, plaque density and overall productivity. These findings suggest that less infective pathogens may have an advantage in spatially structured populations, even when well-mixed models predict that they will not.

Virulence evolution at the front line of spreading epidemics

“…Under these conditions spatial structure is expected to select for lower infectivity and virulence (Boot and Sasaki 1999;Haraguchi and Sasaki 2000;Lion and Boots 2010;Lion and Gandon 2015). Several experiments have confirmed that spatial structure can select for less-aggressive pathogen strategies in bacteriophages (Eshelman et al 2010;Roychoudhury et al 2014;Berngruber et al 2015). But those studies never focused on the spatial distribution of the different types of strains across an epidemic.…”

Phages associated with horses provide new insights into the dominance of lateral gene transfer in virulent bacteriophages evolution in natural systems

“…In the other experiment we used the co-evolution on solid medium that was supposed to provide some spatial complexity that may influence the evolution rates and trajectories (Morgan et al 2005;Kerr et al 2006;Vos et al 2009;Roychoudhury et al 2013;Ashby et al 2014;Hesse et al 2015;Möbius et al 2015). The material from 60 G7C plaques grown on the E. coli 4s lawn was transferred to the LB plate and the growth of the cultures (metastable phagebacteria associations) was observed.…”

Elimination of HSV-2 infected cells is mediated predominantly by paracrine effects of tissue-resident T cell derived cytokines

“…At the start of the simulation, all sites are occupied by susceptible cells and a lawn of tissue-resident T cells at a predefined spatial density (defined as the probability that the focal site at the center of the grid contains TRM). State transitions occur stochastically at probabilities that are determined by the rates of various events that can occur at the site described below (59). These rates determine the wait time, a random variable whose mean is the reciprocal of the corresponding rate.…”

“…To avoid doubly propagating particles or adding dependencies on the order of cell evaluation, the change in values occurs across the grid at the end of each time step. Diffusion is described by a 2D-Gaussian function applied over a 3x3 neighborhood as described in (59).…”