Comparative Modeling of Lytic and Lysogenic Phage-host Systems

Bacteriophages are the most abundant organisms on the planet and play crucial roles in bacterial population dynamics, microbial food webs, and nutrient cycling. Understanding models of bacteriophage population dynamics is necessary to fully understand these ecological processes, but to do so we must mathematically distinguish between the different virus life cycles. Here, we build on two three-dimensional systems of differential equations, similar to Beretta and Kuang (1998) and Reluga et al. (2009) to model lytic and lysogenic virus life cycles. We used these models to generate hypotheses about the ecological costs and benefits of the two life cycles. The models suggest viral abundance and frequency of infected cells increase with habitat productivity. The lytic system is more prone to sustained oscillations, especially with slow-growing cells and more virulent viruses, whereas the lysogenic system only has sustained oscillations when rates of lysis are high relative to cell growth rates, making lysogenic phages qualitatively resemble lytic phages. The models also suggest that lysogenic viruses are capable of infecting all the cells in a population for realistic parameter regimes, and the evolutionary consequences of this prophage fixation are discussed here. Further research can yield new insights into viral population dynamics, test these models and help us better understand the roles of viruses in ecology.