Abstract
Bacterial communities are often exposed to temporal variations in resource availability, which exceed bacterial generation times and thereby affect bacterial coexistence. Bacterial population dynamics are also shaped by bacteriophages, which are a main cause of bacterial mortality. Several strategies are proposed in the literature to describe infections by phages, such as “Killing the Winner”, “Piggyback the loser” (PtL) or “Piggyback the Winner” (PtW). The two temperate phage strategies PtL and PtW are defined by a change from lytic to lysogenic infection when the host density changes, from high to low or from low to high, respectively. To date, the occurrence of different phage strategies and their response to environmental variability is poorly understood. In our study, we developed a microbial trophic network model using ordinary differential equations (ODEs) and performed ‘in silico’ experiments. To model the switch from the lysogenic to the lytic cycle, we modified the lysis rate of infected bacteria and their growth was turned on or off using a density-dependent switching point. We addressed whether and how the different phage strategies facilitate bacteria coexistence competing for limiting resources. We also studied the impact of a fluctuating resource inflow to evaluate the response of the different phage strategies to environmental variability. Our results show that the viral shunt (i.e. nutrient release after bacterial lysis) leads to an enrichment of the system. This enrichment enables bacterial coexistence at lower resource concentrations. We were able to show that an established, purely lytic model leads to stable bacterial coexistence despite fluctuating resources. Both temperate phage models differ in their coexistence patterns. The model of PtW yields stable bacterial coexistence at a limited range of resource supply and is most sensitive to resource fluctuations. Interestingly, the purely lytic phage strategy and PtW both result in stable bacteria coexistence at oligotrophic conditions. The PtL model facilitates stable bacterial coexistence over a large range of stable and fluctuating resource inflow. An increase in bacterial growth rate results in a higher resilience to resource variability for the PtL and the lytic infection model. We propose that both temperate phage strategies represent different mechanisms of phages coping with environmental variability. Our study demonstrates how phage strategies can maintain bacterial coexistence in constant and fluctuating environments.
Highlights
Theory in bacteria population dynamics Bacteria are the most abundant and diverse organisms on earth (Whitman, Coleman & Wiebe, 1998; Godfray, Knapp & Oren, 2004)
Our results show that the viral shunt facilitates bacteria coexistence for all phage strategies by an enrichment of the system
We demonstrate that the same mechanism acts in the temperate phage strategies Piggyback the Winner” (PtW) and Piggyback the loser” (PtL)
Summary
Theory in bacteria population dynamics Bacteria are the most abundant and diverse organisms on earth (Whitman, Coleman & Wiebe, 1998; Godfray, Knapp & Oren, 2004). They occur in all habitats from the atmosphere down to the deep oceanic subsurface (Flemming & Wuertz, 2019) and are adapted to a variety of sometimes extreme conditions of temperature, pH, pollution, or salinity, including substantial temporal fluctuations in these parameters. Viruses exhibit a profound influence on the abundance and diversity of bacteria
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