Mechanisms of Multi-strain Coexistence in Host-Phage Systems with Nested Infection Networks

TL;DR

This paper models how nested infection networks influence the coexistence of bacteria and phages, revealing trade-offs in traits that enable stable multi-strain communities and contrasting with existing models.

Contribution

It introduces a multi-type Lotka-Volterra model for nested infection networks and identifies trait trade-offs that promote coexistence in complex phage-bacteria systems.

Findings

Bacterial growth rate decreases with increased defense.

Viral infection efficiency decreases with host range.

Trade-offs relate to community coexistence and density relationships.

Abstract

Bacteria and their viruses ("bacteriophages") coexist in natural environments forming complex infection networks. Recent empirical findings suggest that phage-bacteria infection networks often possess a nested structure such that there is a hierarchical relationship among who can infect whom. Here we consider how nested infection networks may affect phage and bacteria dynamics using a multi-type Lotka-Volterra framework with cross-infection. Analysis of similar models have, in the past, assumed simpler interaction structures as a first step towards tractability. We solve the proposed model, finding trade-off conditions on the life-history traits of both bacteria and viruses that allow coexistence in communities with nested infection networks. First, we find that bacterial growth rate should decrease with increasing defense against infection. Second, we find that the efficiency of viral infection should decrease with host range. Next, we establish a relationship between relative densities and the curvature of life history trade-offs. We compare and contrast the current findings to the "Kill-the-Winner" model of multi-species phage-bacteria communities. Finally, we discuss a suite of testable hypotheses stemming from the current model concerning relationships between infection range, life history traits and coexistence in complex phage-bacteria communities.