Abstract
Virulent phages can expose their bacterial hosts to devastating epidemics, in principle leading to complete elimination of their hosts. Although experiments indeed confirm a large reduction of susceptible bacteria, there are no reports of complete extinctions. We here address this phenomenon from the perspective of spatial organization of bacteria and how this can influence the final survival of them. By modelling the transient dynamics of bacteria and phages when they are introduced into an environment with finite resources, we quantify how time delayed lysis, the spatial separation of initial bacterial positions, and the self-protection of bacteria growing in spherical colonies favour bacterial survival. Our results suggest that spatial structures on the millimetre and submillimetre scale play an important role in maintaining microbial diversity.
Highlights
Virulent phages can expose their bacterial hosts to devastating epidemics, in principle leading to complete elimination of their hosts
The addition of phages leads to an initial collapse of the susceptible bacterial population after which they grow to a high density which matches the steady-state prediction of the generalized Lotka-Volterra equations
We focus on spatial structures, both on the millimetre and submillimetre scale, and their ability to moderate the virulence of the phages
Summary
Virulent phages can expose their bacterial hosts to devastating epidemics, in principle leading to complete elimination of their hosts. In contrast to the oscillating lynx-hare systems from macroscopic ecology[24], the microbial ecology experiments appear much more damped[14,25] In such microbial experiments, the addition of phages leads to an initial collapse of the susceptible bacterial population after which they grow to a high density which matches the steady-state prediction of the generalized Lotka-Volterra equations. It is possible that phages irreversibly bind to the bacterial debris left over from bacterial lysis and inactive them leading to more and more phage decay as the phage invasion takes hold[16,18] Another solution is the inclusion variability in the adsorption rate of phages, e.g. by assuming two subspecies in a bacterial population, one with a high adsorption rate and one with a low adsorption rate[23,27]. It has been shown that a microcolony can grow exponentially in volume for a substantial period of time[8,9], demonstrating the importance of exponential growth even in a spatially structured environment
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